diff options
| author | Juan Marín Noguera <juan.marinn@um.es> | 2020-02-20 13:15:34 +0100 |
|---|---|---|
| committer | Juan Marín Noguera <juan.marinn@um.es> | 2020-02-20 13:15:34 +0100 |
| commit | 29eb708670963c0ca5bd315c83a3cec8dafef1a7 (patch) | |
| tree | 1a53fce36c4ef876bd73b98fff88e79cc4377803 /algl | |
Commit inicial, primer cuatrimestre.
Diffstat (limited to 'algl')
| -rw-r--r-- | algl/n.lyx | 208 | ||||
| -rw-r--r-- | algl/n1.lyx | 3673 | ||||
| -rw-r--r-- | algl/n2.lyx | 2102 | ||||
| -rw-r--r-- | algl/n3.lyx | 652 | ||||
| -rw-r--r-- | algl/n4.lyx | 1759 | ||||
| -rw-r--r-- | algl/n5.lyx | 1323 |
6 files changed, 9717 insertions, 0 deletions
diff --git a/algl/n.lyx b/algl/n.lyx new file mode 100644 index 0000000..0b82057 --- /dev/null +++ b/algl/n.lyx @@ -0,0 +1,208 @@ +#LyX 2.3 created this file. For more info see http://www.lyx.org/ +\lyxformat 544 +\begin_document +\begin_header +\save_transient_properties true +\origin unavailable +\textclass book +\use_default_options true +\maintain_unincluded_children false +\language spanish +\language_package default +\inputencoding auto +\fontencoding global +\font_roman "default" "default" +\font_sans "default" "default" +\font_typewriter "default" "default" +\font_math "auto" "auto" +\font_default_family default +\use_non_tex_fonts false +\font_sc false +\font_osf false +\font_sf_scale 100 100 +\font_tt_scale 100 100 +\use_microtype false +\use_dash_ligatures true +\graphics default +\default_output_format default +\output_sync 0 +\bibtex_command default +\index_command default +\paperfontsize default +\spacing single +\use_hyperref false +\papersize a5paper +\use_geometry true +\use_package amsmath 1 +\use_package amssymb 1 +\use_package cancel 1 +\use_package esint 1 +\use_package mathdots 1 +\use_package mathtools 1 +\use_package mhchem 1 +\use_package stackrel 1 +\use_package stmaryrd 1 +\use_package undertilde 1 +\cite_engine basic +\cite_engine_type default +\biblio_style plain +\use_bibtopic false +\use_indices false +\paperorientation portrait +\suppress_date false +\justification true +\use_refstyle 1 +\use_minted 0 +\index Index +\shortcut idx +\color #008000 +\end_index +\leftmargin 0.2cm +\topmargin 0.7cm +\rightmargin 0.2cm +\bottommargin 0.7cm +\secnumdepth 3 +\tocdepth 3 +\paragraph_separation indent +\paragraph_indentation default +\is_math_indent 0 +\math_numbering_side default +\quotes_style swiss +\dynamic_quotes 0 +\papercolumns 1 +\papersides 1 +\paperpagestyle empty +\tracking_changes false +\output_changes false +\html_math_output 0 +\html_css_as_file 0 +\html_be_strict false +\end_header + +\begin_body + +\begin_layout Title +Álgebra lineal +\end_layout + +\begin_layout Date +\begin_inset Note Note +status open + +\begin_layout Plain Layout + +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +def +\backslash +cryear{2017} +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +\begin_inset CommandInset include +LatexCommand input +filename "../license.lyx" + +\end_inset + + +\end_layout + +\begin_layout Standard +Bibliografía: +\end_layout + +\begin_layout Itemize +Material clases teóricas, Álgebra Lineal, Universidad de Murcia (anónimo). +\end_layout + +\begin_layout Chapter +Espacios vectoriales +\end_layout + +\begin_layout Standard +\begin_inset CommandInset include +LatexCommand input +filename "n1.lyx" + +\end_inset + + +\end_layout + +\begin_layout Chapter +Aplicaciones Lineales +\end_layout + +\begin_layout Standard +\begin_inset CommandInset include +LatexCommand input +filename "n2.lyx" + +\end_inset + + +\end_layout + +\begin_layout Chapter +Sistemas de ecuaciones lineales +\end_layout + +\begin_layout Standard +\begin_inset CommandInset include +LatexCommand input +filename "n3.lyx" + +\end_inset + + +\end_layout + +\begin_layout Chapter +Determinantes +\end_layout + +\begin_layout Standard +\begin_inset CommandInset include +LatexCommand input +filename "n4.lyx" + +\end_inset + + +\end_layout + +\begin_layout Chapter +Diagonalización de endomorfismos +\end_layout + +\begin_layout Standard +\begin_inset CommandInset include +LatexCommand input +filename "n5.lyx" + +\end_inset + + +\end_layout + +\end_body +\end_document diff --git a/algl/n1.lyx b/algl/n1.lyx new file mode 100644 index 0000000..47d85c9 --- /dev/null +++ b/algl/n1.lyx @@ -0,0 +1,3673 @@ +#LyX 2.3 created this file. For more info see http://www.lyx.org/ +\lyxformat 544 +\begin_document +\begin_header +\save_transient_properties true +\origin unavailable +\textclass book +\use_default_options true +\maintain_unincluded_children false +\language spanish +\language_package default +\inputencoding auto +\fontencoding global +\font_roman "default" "default" +\font_sans "default" "default" +\font_typewriter "default" "default" +\font_math "auto" "auto" +\font_default_family default +\use_non_tex_fonts false +\font_sc false +\font_osf false +\font_sf_scale 100 100 +\font_tt_scale 100 100 +\use_microtype false +\use_dash_ligatures true +\graphics default +\default_output_format default +\output_sync 0 +\bibtex_command default +\index_command default +\paperfontsize default +\spacing single +\use_hyperref false +\papersize default +\use_geometry false +\use_package amsmath 1 +\use_package amssymb 1 +\use_package cancel 1 +\use_package esint 1 +\use_package mathdots 1 +\use_package mathtools 1 +\use_package mhchem 1 +\use_package stackrel 1 +\use_package stmaryrd 1 +\use_package undertilde 1 +\cite_engine basic +\cite_engine_type default +\biblio_style plain +\use_bibtopic false +\use_indices false +\paperorientation portrait +\suppress_date false +\justification true +\use_refstyle 1 +\use_minted 0 +\index Index +\shortcut idx +\color #008000 +\end_index +\secnumdepth 3 +\tocdepth 3 +\paragraph_separation indent +\paragraph_indentation default +\is_math_indent 0 +\math_numbering_side default +\quotes_style swiss +\dynamic_quotes 0 +\papercolumns 1 +\papersides 1 +\paperpagestyle default +\tracking_changes false +\output_changes false +\html_math_output 0 +\html_css_as_file 0 +\html_be_strict false +\end_header + +\begin_body + +\begin_layout Section +Cuerpos +\end_layout + +\begin_layout Standard +Conjunto +\begin_inset Formula $K$ +\end_inset + + con dos operaciones, +\series bold +suma +\series default + ( +\begin_inset Formula $+$ +\end_inset + +) y +\series bold +producto +\series default + ( +\begin_inset Formula $\cdot$ +\end_inset + +), tales que +\begin_inset Formula $\forall a,b,c\in K$ +\end_inset + +: +\end_layout + +\begin_layout Enumerate + +\series bold +Propiedad asociativa de la suma: +\series default + +\begin_inset Formula $a+(b+c)=(a+b)+c$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate + +\series bold +Propiedad conmutativa de la suma: +\begin_inset Formula $a+b=b+a$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate + +\series bold +Elemento neutro para la suma +\series default + o +\series bold +nulo: +\series default + +\begin_inset Formula $\exists!0\in K:\forall a\in K,0+a=a$ +\end_inset + +. +\begin_inset Newline newline +\end_inset + +Pongamos que existe otro +\begin_inset Formula $0$ +\end_inset + + ( +\begin_inset Formula $0'$ +\end_inset + +), entonces +\begin_inset Formula $0=0+0'=0'$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate + +\series bold +Inverso para la suma +\series default + u +\series bold +opuesto: +\series default + +\begin_inset Formula $\forall a\in K,\exists!a':a+a'=0$ +\end_inset + +. + +\begin_inset Formula $-a:=a'$ +\end_inset + +. +\begin_inset Newline newline +\end_inset + +Pongamos que existe otro opuesto +\begin_inset Formula $a''$ +\end_inset + +, entonces +\begin_inset Formula $a'=0+a'=(a''+a)+a'=a''+(a+a')=a''+0=a''$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate + +\series bold +Propiedad asociativa del producto: +\series default + +\begin_inset Formula $a\cdot(b\cdot c)=(a\cdot b)\cdot c$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate + +\series bold +Propiedad conmutativa del producto: +\series default + +\begin_inset Formula $a\cdot b=b\cdot a$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate + +\series bold +Elemento neutro para el producto +\series default + o +\series bold +unidad: +\series default + +\begin_inset Formula $\exists!1\in K:\forall a\in K,1\cdot a=a$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate + +\series bold +Inverso para el producto: +\series default + +\begin_inset Formula $\forall a\in K\backslash\{0\},\exists!a'':a\cdot a''=1$ +\end_inset + +; +\begin_inset Formula $a^{-1}:=\frac{1}{a}:=a''$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate + +\series bold +Propiedad distributiva: +\series default + +\begin_inset Formula $a\cdot(b+c)=a\cdot b+a\cdot c$ +\end_inset + +. +\end_layout + +\begin_layout Standard +La congruencia +\begin_inset Formula $\mathbb{Z}_{2}=\{0,1\}$ +\end_inset + + con operaciones +\begin_inset Formula $0+0=1+1=0$ +\end_inset + +, +\begin_inset Formula $0+1=1+0=1$ +\end_inset + +, +\begin_inset Formula $0\cdot0=0\cdot1=1\cdot0=0$ +\end_inset + + y +\begin_inset Formula $1\cdot1=1$ +\end_inset + + es un cuerpo. + Siempre existe un cuerpo +\begin_inset Formula $F_{p^{n}}$ +\end_inset + +, formado por +\begin_inset Formula $p^{n}$ +\end_inset + + elementos, donde +\begin_inset Formula $n\in\mathbb{N}$ +\end_inset + + y +\begin_inset Formula $p$ +\end_inset + + es primo. + Algunas propiedades: +\begin_inset Formula $\forall a,b,c\in K$ +\end_inset + +: +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $a+b=a+c\implies b=c$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $0a=0$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $(-a)b=a(-b)=-(ab)$ +\end_inset + +; +\begin_inset Formula $(-1)a=-a$ +\end_inset + +; +\begin_inset Formula $(-a)(-b)=ab$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $ab=0\implies a=0\lor b=0$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $ab=ac\implies a=0\lor b=c$ +\end_inset + +. +\end_layout + +\begin_layout Subsection +El cuerpo de los números complejos +\end_layout + +\begin_layout Standard +Si consideramos +\begin_inset Formula $\mathbb{R}\times\mathbb{R}=\{(a,b)|a,b\in\mathbb{R}\}$ +\end_inset + +, con +\begin_inset Formula $(a,b)+(c,d)=(a+c,b+d)$ +\end_inset + + y +\begin_inset Formula $(a,b)\cdot(c,d)=(ac-bd,ad+bc)$ +\end_inset + +, obtenemos el cuerpo de los números complejos ( +\begin_inset Formula $\mathbb{C}$ +\end_inset + +). + El conjunto de elementos de +\begin_inset Formula $\mathbb{C}$ +\end_inset + + con forma +\begin_inset Formula $(a,0)$ +\end_inset + + es una copia del cuerpo +\begin_inset Formula $\mathbb{R}$ +\end_inset + +. + Llamamos +\series bold +unidad imaginaria +\series default + a +\begin_inset Formula $i=(0,1)$ +\end_inset + +, de forma que +\begin_inset Formula $i^{2}=i\cdot i=(-1,0)=-1$ +\end_inset + +. + Dado que +\begin_inset Formula $(b,0)i=(0,b)$ +\end_inset + +, y como +\begin_inset Formula $(b,0)$ +\end_inset + + es el número real +\begin_inset Formula $b$ +\end_inset + +, tenemos +\begin_inset Formula $(a,b)=a+bi$ +\end_inset + +, lo que denominamos la +\series bold +forma binomial. + +\series default + +\begin_inset Formula $a$ +\end_inset + + es la +\series bold +componente real, +\series default + y +\begin_inset Formula $b$ +\end_inset + + la +\series bold +componente imaginaria. + +\series default + Si +\begin_inset Formula $z=a+bi$ +\end_inset + +, llamamos +\series bold +conjugado +\series default + de +\begin_inset Formula $z$ +\end_inset + + a +\begin_inset Formula $\overline{z}=a-bi$ +\end_inset + +, de forma que +\begin_inset Formula $z=\overline{z}\iff z\in\mathbb{R}$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Podemos representar un número complejo +\begin_inset Formula $z=a+bi$ +\end_inset + + como un punto del plano, con coordenadas +\begin_inset Formula $(a,b)$ +\end_inset + +. + La distancia del punto al origen de coordenadas, llamada +\series bold +módulo +\series default +, es +\begin_inset Formula $r=|z|=\sqrt{a^{2}+b^{2}}=\sqrt{z\overline{z}}$ +\end_inset + +. + El ángulo con el eje +\begin_inset Formula $OX$ +\end_inset + +, llamado +\series bold +argumento +\series default +, cumple que +\begin_inset Formula $a+bi=r(\cos(\alpha)+i\sin(\alpha))$ +\end_inset + +. + Esta es la +\series bold +forma polar +\series default + o +\series bold +módulo argumental +\series default + del complejo. + La multiplicación en forma polar es: +\begin_inset Formula $[r(\cos(\alpha)+i\sin(\alpha))][r'(\cos(\alpha')+i\sin(\alpha'))]=rr'(\cos(\alpha+\alpha')+i\sin(\alpha+\alpha'))$ +\end_inset + +. +\end_layout + +\begin_layout Standard +El +\series bold +Teorema Fundamental del Álgebra +\series default + nos dice que todo polinomio +\begin_inset Formula $P(x)=a_{0}+a_{1}X+a_{2}X^{2}+\dots+a_{n}X^{n}$ +\end_inset + +, con +\begin_inset Formula $n\geq1$ +\end_inset + +, +\begin_inset Formula $a_{i}\in\mathbb{C}$ +\end_inset + + y +\begin_inset Formula $a_{n}\neq0$ +\end_inset + +, tiene raíz compleja. +\end_layout + +\begin_layout Subsection +Característica de un cuerpo. +\end_layout + +\begin_layout Standard +\begin_inset Formula +\[ +\forall a\in K,n\in\mathbb{N},na=\underset{n\text{ veces}}{a+a+\cdots+a} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +En particular, +\begin_inset Formula +\[ +n1=\underset{n\text{ veces}}{1+1+\cdots+1} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Por tanto, +\begin_inset Formula $na=(n1)a$ +\end_inset + +, +\begin_inset Formula $n1+m1=(n+m)1$ +\end_inset + + y +\begin_inset Formula $(n1)(m1)=(nm)1$ +\end_inset + + para cualquier cuerpo +\begin_inset Formula $K$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Un cuerpo tiene +\series bold +característica cero +\series default + si +\begin_inset Formula $\forall n>0,n1\neq0$ +\end_inset + +. + De lo contrario, se dice que tiene +\series bold +característica +\begin_inset Formula $n$ +\end_inset + + +\series default +, siendo +\begin_inset Formula $n$ +\end_inset + + el menor natural tal que +\begin_inset Formula $n1=0$ +\end_inset + +. + Así, +\begin_inset Formula $na=(n1)a\implies na=0$ +\end_inset + +. + Dado que +\begin_inset Formula $ab=0\iff a=0\lor b=0$ +\end_inset + +, tenemos que +\begin_inset Formula $\exists p,q<n:n=pq\implies0=n1=(p1)(q1)\implies p1=0\lor q1=0$ +\end_inset + +, por lo que la característica de un cuerpo es cero o un nº primo. +\end_layout + +\begin_layout Section +Espacios vectoriales +\end_layout + +\begin_layout Standard +Un +\series bold +espacio vectorial +\series default + sobre +\begin_inset Formula $K$ +\end_inset + +, o +\begin_inset Formula $K$ +\end_inset + +-espacio vectorial, es una terna +\begin_inset Formula $(V,+,\cdot)$ +\end_inset + + donde +\begin_inset Formula $V\neq\emptyset$ +\end_inset + +, +\begin_inset Formula $+$ +\end_inset + + es una operación +\begin_inset Formula $V\times V\longrightarrow V$ +\end_inset + + y +\begin_inset Formula $\cdot$ +\end_inset + + es una operación +\begin_inset Formula $K\times V\longrightarrow V$ +\end_inset + +, tales que +\begin_inset Formula $\forall u,v,w\in V,\alpha,\beta\in K$ +\end_inset + +: +\end_layout + +\begin_layout Enumerate + +\series bold +Suma asociativa: +\series default + +\begin_inset Formula $u+(v+w)=(u+v)+w$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate + +\series bold +Suma conmutativa: +\series default + +\begin_inset Formula $u+v=v+u$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate + +\series bold +Vector cero +\series default + o +\series bold +nulo: +\series default + +\begin_inset Formula $\exists0_{V}:\forall u\in V,0_{V}+u=u$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate + +\series bold +Opuesto para la suma: +\series default + +\begin_inset Formula $\forall u\in V,\exists u':u+u'=0_{V}$ +\end_inset + +; +\begin_inset Formula $u':=-u$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\alpha\cdot(u+v)=\alpha\cdot u+\alpha\cdot v$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $(\alpha+\beta)\cdot u=\alpha\cdot u+\beta\cdot u$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $(\alpha\cdot\beta)\cdot u=\alpha\cdot(\beta\cdot u)$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $1_{K}\cdot u=u$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Llamamos +\series bold +vectores +\series default + a los elementos de +\begin_inset Formula $V$ +\end_inset + + y +\series bold +escalares +\series default + a los de +\begin_inset Formula $K$ +\end_inset + +. + Todo cuerpo es espacio vectorial sobre sí mismo. + +\begin_inset Formula $\mathbb{R}$ +\end_inset + + es espacio vectorial sobre +\begin_inset Formula $\mathbb{Q}$ +\end_inset + +, y +\begin_inset Formula $\mathbb{C}$ +\end_inset + + sobre +\begin_inset Formula $\mathbb{R}$ +\end_inset + + y +\begin_inset Formula $\mathbb{Q}$ +\end_inset + +. +\end_layout + +\begin_layout Standard +El plano real +\begin_inset Formula $\mathbb{R}^{2}=\{(x,y)|x,y\in\mathbb{R}\}$ +\end_inset + +, con las operaciones +\begin_inset Formula $(x,y)+(x',y')=(x+x',y+y')$ +\end_inset + + y +\begin_inset Formula $\alpha(x,y)=(\alpha x,\alpha y)$ +\end_inset + +, es un +\begin_inset Formula $\mathbb{R}$ +\end_inset + +-espacio vectorial. + El conjunto +\begin_inset Formula $K^{n}$ +\end_inset + + de las +\begin_inset Formula $n$ +\end_inset + +-uplas de elementos de +\begin_inset Formula $K$ +\end_inset + +, +\begin_inset Formula $K^{n}=\{(x_{1},x_{2},\dots,x_{n}|x_{1},x_{2},\dots,x_{n}\in K\}$ +\end_inset + + es un +\begin_inset Formula $K$ +\end_inset + +-espacio vectorial con las operaciones +\begin_inset Formula $(x_{1},\dots,x_{n})+(y_{1},\dots,y_{n})=(x_{1}+y_{1},\dots,x_{n}+y_{n})$ +\end_inset + + y +\begin_inset Formula $\alpha(x_{1},\dots x_{n})=(\alpha x_{1},\dots,\alpha x_{n})$ +\end_inset + +. + También, si +\begin_inset Formula $V_{1},\dots,V_{n}$ +\end_inset + + son +\begin_inset Formula $K$ +\end_inset + +-espacios vectoriales, el conjunto +\begin_inset Formula $V_{1}\times\dots\times V_{n}=\{(v_{1},v_{2},\dots,v_{n})|v_{1}\in V_{1},v_{2}\in V_{2},\dots,v_{n}\in V_{n}\}$ +\end_inset + +, con operaciones similares, es un +\begin_inset Formula $K$ +\end_inset + +-espacio vectorial llamado +\series bold +espacio vectorial producto +\series default + de los +\begin_inset Formula $V_{i}$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Una +\series bold +matriz +\series default + +\begin_inset Formula $A$ +\end_inset + + de tamaño +\begin_inset Formula $m\times n$ +\end_inset + + (con +\begin_inset Formula $m,n\in\mathbb{N}$ +\end_inset + +) sobre +\begin_inset Formula $K$ +\end_inset + + es una disposición en +\begin_inset Formula $m$ +\end_inset + + filas y +\begin_inset Formula $n$ +\end_inset + + columnas de +\begin_inset Formula $m\cdot n$ +\end_inset + + elementos de +\begin_inset Formula $K$ +\end_inset + +. + La matriz es +\series bold +cuadrada +\series default + si +\begin_inset Formula $m=n$ +\end_inset + +, +\series bold +fila +\series default + si +\begin_inset Formula $m=1$ +\end_inset + + y +\series bold +columna +\series default + si +\begin_inset Formula $n=1$ +\end_inset + +. + Llamamos +\begin_inset Formula $M_{m,n}(K)$ +\end_inset + + al conjunto de las matrices +\begin_inset Formula $m\times n$ +\end_inset + + sobre +\begin_inset Formula $K$ +\end_inset + +, y +\begin_inset Formula $M_{n,n}(K)=M_{n}(K)$ +\end_inset + +. + Se representan de la siguiente forma: +\begin_inset Formula +\[ +A=\left(\begin{array}{cccc} +a_{11} & a_{12} & \cdots & a_{1n}\\ +a_{21} & a_{22} & \cdots & a_{2n}\\ +\vdots & \vdots & \ddots & \vdots\\ +a_{m1} & a_{m2} & \cdots & a_{mn} +\end{array}\right),\,a_{ij}\in K\forall1\leq i\leq m,1\leq j\leq n +\] + +\end_inset + + +\begin_inset Formula $\forall A=(a_{ij}),B=(b_{ij})\in M_{m,n}(K),A+B=(c_{ij})\in M_{m,n}(K)$ +\end_inset + +, donde +\begin_inset Formula $c_{ij}=a_{ij}+b_{ij}$ +\end_inset + + para cada elemento de la matriz. + También, +\begin_inset Formula $\forall\alpha\in K,A\in M_{m,n}(K),\alpha A=(c_{ij})\in M_{m,n}(K)$ +\end_inset + +, donde +\begin_inset Formula $c_{ij}=\alpha a_{ij}$ +\end_inset + +. + Con estas operaciones, +\begin_inset Formula $M_{m,n}(K)$ +\end_inset + + es un +\begin_inset Formula $K$ +\end_inset + +-espacio vectorial. +\end_layout + +\begin_layout Standard +Un +\series bold +polinomio +\series default + en una +\series bold +indeterminada +\series default + +\begin_inset Formula $X$ +\end_inset + + con +\series bold +coeficientes +\series default + en +\begin_inset Formula $K$ +\end_inset + + es una expresión de la forma +\begin_inset Formula +\[ +a_{0}+a_{1}X+a_{2}X^{2}+\dots+a_{n}X^{n} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Donde +\begin_inset Formula $n$ +\end_inset + + es un entero no negativo, +\begin_inset Formula $a_{i}\in K\forall i=0,1,\dots n$ +\end_inset + +. + El conjunto de polinomios sobre +\begin_inset Formula $K$ +\end_inset + + se llama +\begin_inset Formula $K(X)$ +\end_inset + + y es un espacio vectorial con las operaciones: +\begin_inset Formula +\begin{eqnarray*} +(a_{0}+\dots+a_{n}X^{n})+(b_{0}+\dots+b_{n}X^{n}) & = & (a_{0}+b_{0})+\dots+(a_{n}+b_{n})X^{n}\\ +\alpha(a_{0}+a_{1}X+\dots+a_{n}X^{n}) & = & \alpha a_{0}+\alpha a_{1}X+\dots+\alpha a_{n}X^{n} +\end{eqnarray*} + +\end_inset + + +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $\mathcal{S}\neq\emptyset$ +\end_inset + +, el conjunto +\begin_inset Formula $\mathcal{F}(\mathcal{S},K)=\{f:\mathcal{S}\rightarrow K\}$ +\end_inset + +, formado por todas las aplicaciones de +\begin_inset Formula $\mathcal{S}$ +\end_inset + + en +\begin_inset Formula $K$ +\end_inset + +, con operaciones +\begin_inset Formula $(f+g)(s)=f(s)+g(s)$ +\end_inset + + y +\begin_inset Formula $(\alpha f)(s)=\alpha f(s)$ +\end_inset + +, es un +\begin_inset Formula $K$ +\end_inset + +-espacio vectorial. + Con estas mismas operaciones, el conjunto +\begin_inset Formula $\mathcal{C}([a,b],\mathbb{R})=\{f:[a,b]\rightarrow\mathbb{R}|f\text{ continua}\}$ +\end_inset + + es un +\begin_inset Formula $\mathbb{R}$ +\end_inset + +-espacio vectorial. +\end_layout + +\begin_layout Standard +Propiedades de los espacios vectoriales: +\begin_inset Formula $\forall u,v,w\in V,\alpha,\beta\in K$ +\end_inset + +: +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $u+v=u+w\implies v=w$ +\end_inset + + +\begin_inset Formula +\[ +u+v=u+w\implies(-u)+(u+v)=(-u)+(u+w)=((-u)+u)+v=((-u)+u)+w=v=w +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $0u=0_{V}$ +\end_inset + + +\begin_inset Formula +\[ +0u+0u=(0+0)u=0u=0u+0_{V}\implies0u=0_{V} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\alpha0_{V}=0_{V}$ +\end_inset + + +\begin_inset Formula +\[ +\alpha0_{V}+0_{V}=\alpha0_{V}=\alpha(0_{V}+0_{V})=\alpha0_{V}+\alpha0_{V}\implies\alpha0_{V}=0_{V} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $u\in V,\alpha u=0_{V}\implies\alpha=0\lor u=0_{V}$ +\end_inset + +; +\begin_inset Formula $\alpha u=\alpha v\implies\alpha=0\lor u=v$ +\end_inset + +; +\begin_inset Formula $\alpha u=\beta u\implies\alpha=\beta\lor u=0_{V}$ +\end_inset + + +\begin_inset Formula +\[ +\begin{array}{c} +\alpha u=0_{V}\\ +\alpha\neq0 +\end{array}\implies u=(\alpha^{-1}\cdot\alpha)u=\alpha^{-1}(\alpha u)=\alpha^{-1}\cdot0_{V}=0_{V} +\] + +\end_inset + + +\begin_inset Formula +\[ +\begin{array}{c} +\alpha u=\alpha v\\ +\alpha\neq0 +\end{array}\implies\alpha^{-1}(\alpha u)=\alpha^{-1}(\alpha v)=1\cdot u=1\cdot v=u=v +\] + +\end_inset + +Para la última demostración, usamos (5): +\begin_inset Formula +\[ +\begin{array}{c} +\begin{array}{c} +\alpha u=\beta u\\ +u\neq0_{V} +\end{array}\implies0_{V}=\alpha u+(-(\beta u))\overset{(5)}{=}\alpha u+(-\beta)u=(\alpha+(-\beta))u\implies\\ +\implies\alpha+(-\beta)=0\implies\alpha=\beta +\end{array} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $u\in V,(-\alpha)u=\alpha(-u)=-(\alpha u)$ +\end_inset + + +\begin_inset Formula +\[ +(-\alpha)u+\alpha u=(-\alpha+\alpha)u=0u=0_{V}\implies(-\alpha)u=-(\alpha u) +\] + +\end_inset + + +\begin_inset Formula +\[ +\alpha(-u)+\alpha u=\alpha(-u+u)=\alpha\cdot0_{V}=0_{V}\implies\alpha(-u)=-(\alpha u) +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +También podemos llamar +\begin_inset Formula $0$ +\end_inset + + a +\begin_inset Formula $0_{V}$ +\end_inset + + si esto no conlleva ambigüedad. +\end_layout + +\begin_layout Section +Subespacios vectoriales +\end_layout + +\begin_layout Standard +\begin_inset Formula $U\subseteq V$ +\end_inset + + ( +\begin_inset Formula $U\neq\emptyset$ +\end_inset + +) es un +\series bold +subespacio vectorial +\series default + de +\begin_inset Formula $V$ +\end_inset + + ( +\begin_inset Formula $U\leq V$ +\end_inset + +) si +\begin_inset Formula $\forall u,v\in U,u+v\in U$ +\end_inset + + y +\begin_inset Formula $\forall u\in U,\alpha\in K,\alpha u\in U$ +\end_inset + +. + De esta forma +\begin_inset Formula $U$ +\end_inset + + es también un +\begin_inset Formula $K$ +\end_inset + +-espacio vectorial. +\end_layout + +\begin_layout Standard +Los subconjuntos +\begin_inset Formula $\{0\}$ +\end_inset + + y +\begin_inset Formula $V$ +\end_inset + + son subespacios vectoriales de +\begin_inset Formula $V$ +\end_inset + +, y +\begin_inset Formula $\{(x_{1},\dots,x_{n})\in K^{n}|x_{1}+\dots+x_{n}=0\}$ +\end_inset + + es un subespacio vectorial de +\begin_inset Formula $K^{n}$ +\end_inset + +. + El conjunto +\begin_inset Formula $\mathcal{P}_{n}$ +\end_inset + + de polinomios con coeficientes reales con grado menor o igual a +\begin_inset Formula $n$ +\end_inset + +, junto con el +\begin_inset Formula $0$ +\end_inset + +, es un subespacio vectorial de +\begin_inset Formula $\mathbb{R}[X]$ +\end_inset + +. + También lo es +\begin_inset Formula $U_{a,b}=\{f\in\mathcal{C}([a,b],\mathbb{R}):f(a)=f(b)\}$ +\end_inset + + respecto de +\begin_inset Formula $\mathcal{C}([a,b],\mathbb{R})$ +\end_inset + +. +\end_layout + +\begin_layout Section +Combinaciones lineales. + Sistemas de generadores +\end_layout + +\begin_layout Standard +\begin_inset Formula $u\in V$ +\end_inset + + es +\series bold +combinación lineal +\series default + de +\begin_inset Formula $v_{1},\dots,v_{n}\in V$ +\end_inset + + si +\begin_inset Formula $\exists\alpha_{1},\dots,\alpha_{n}\in K:u=\alpha_{1}v_{1}+\dots+\alpha_{n}v_{n}$ +\end_inset + +. + Se dice que es combinación lineal de vectores de +\begin_inset Formula $\mathcal{S}$ +\end_inset + + (con +\begin_inset Formula $\mathcal{S}\subseteq V$ +\end_inset + +) si +\begin_inset Formula $\exists n\in\mathbb{N},v_{1},\dots,v_{n}\in\mathcal{S}:u=\alpha_{1}v_{1}+\dots+\alpha_{n}v_{n}$ +\end_inset + +. + Los escalares +\begin_inset Formula $\alpha_{i}$ +\end_inset + + se llaman +\series bold +coeficientes +\series default + de la combinación. + Así, un subconjunto no vacío +\begin_inset Formula $U\subseteq V$ +\end_inset + + es un subespacio vectorial de +\begin_inset Formula $V$ +\end_inset + + si cualquier combinación lineal de vectores de +\begin_inset Formula $U$ +\end_inset + + también está en +\begin_inset Formula $U$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $\mathcal{S}$ +\end_inset + + es un subconjunto no vacío de +\begin_inset Formula $V$ +\end_inset + +, el conjunto +\begin_inset Formula $<\mathcal{S}>$ +\end_inset + + de todas las combinaciones lineales de vectores en +\begin_inset Formula $\mathcal{S}$ +\end_inset + + es el menor subespacio vectorial tal que +\begin_inset Formula $\mathcal{S}\subseteq<{\cal S}>$ +\end_inset + +. + +\series bold +Demostración: +\series default + +\begin_inset Formula $u\in\mathcal{S}\implies1\cdot u\in<\mathcal{S}>$ +\end_inset + +. + Si +\begin_inset Formula $u,v\in<\mathcal{S}>$ +\end_inset + +, entonces existirán +\begin_inset Formula $u_{1},\dots,u_{k},v_{1},\dots,v_{l}\in\mathcal{S}$ +\end_inset + + y +\begin_inset Formula $\alpha_{1},\dots\alpha_{k},\beta_{1},\dots,\beta_{l}\in K$ +\end_inset + + tales que +\begin_inset Formula $u=\alpha_{1}u_{1}+\dots+\alpha_{k}u_{k}$ +\end_inset + + y +\begin_inset Formula $v=\beta_{1}v_{1}+\dots+\beta_{l}+v_{l}$ +\end_inset + +, por lo que +\begin_inset Formula $u+v$ +\end_inset + + también es combinación lineal de vectores en +\begin_inset Formula $\mathcal{S}$ +\end_inset + + y por tanto está en +\begin_inset Formula $<S>$ +\end_inset + +. + Si +\begin_inset Formula $\alpha\in K$ +\end_inset + +, tenemos que +\begin_inset Formula $u=\alpha\alpha_{1}u_{1}+\dots+\alpha\alpha_{k}u_{k}\in<\mathcal{S}>$ +\end_inset + +. + Finalmente, si +\begin_inset Formula $U$ +\end_inset + + es un subespacio vectorial de +\begin_inset Formula $V$ +\end_inset + + que contiene a +\begin_inset Formula $\mathcal{S}$ +\end_inset + +, como toda combinación de vectores de +\begin_inset Formula $U$ +\end_inset + + está en +\begin_inset Formula $U$ +\end_inset + +, entonces +\begin_inset Formula $<\mathcal{S}>\subseteq U$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Un subconjunto +\begin_inset Formula $\mathcal{S}\subseteq V$ +\end_inset + + es un +\series bold +sistema de generadores +\series default + de +\begin_inset Formula $V$ +\end_inset + + si +\begin_inset Formula $<\mathcal{S}>=V$ +\end_inset + +. + +\begin_inset Formula $V$ +\end_inset + + es +\series bold +de dimensión finita +\series default + o +\series bold +finitamente generado +\series default + si tiene un sistema de generadores finito. + Estas definiciones también son válidas para subespacios vectoriales. + +\begin_inset Formula $U$ +\end_inset + + es el subespacio +\series bold +generado +\series default + por +\begin_inset Formula $\mathcal{S}$ +\end_inset + + si +\begin_inset Formula $U=<\mathcal{S}>$ +\end_inset + +. +\end_layout + +\begin_layout Section +Dependencia e independencia lineal +\end_layout + +\begin_layout Standard +Un conjunto +\begin_inset Formula ${\cal S}\subseteq V$ +\end_inset + + es +\series bold +linealmente independiente +\series default + si la única forma de obtener el vector nulo como combinación lineal de + vectores de +\begin_inset Formula ${\cal S}$ +\end_inset + + es tomando todos los coeficientes nulos. + De lo contrario es +\series bold +linealmente dependiente +\series default +. + Así, +\begin_inset Formula $\{v\}$ +\end_inset + + es linealmente independiente si y sólo si +\begin_inset Formula $v\neq0$ +\end_inset + +, con lo que cualquier conjunto +\begin_inset Formula $\{0\}\subseteq{\cal S}$ +\end_inset + + es linealmente dependiente. + En +\begin_inset Formula $\mathbb{C_{R}}$ +\end_inset + +, +\begin_inset Formula $\{1,i\}$ +\end_inset + + ( +\begin_inset Formula $\mathbb{C}$ +\end_inset + + con escalares reales) es linealmente independiente, mientras que en +\begin_inset Formula $\mathbb{C_{C}}$ +\end_inset + + es linealmente dependiente porque +\begin_inset Formula $1+(i)i=0$ +\end_inset + +. + Un subconjunto de un conjunto linealmente independiente también es linealmente + dependiente. +\end_layout + +\begin_layout Standard +Un conjunto +\begin_inset Formula $\{v_{1},\dots,v_{m}\}$ +\end_inset + + con al menos dos vectores es linealmente dependiente si y sólo si alguno + de ellos es combinación lineal del resto. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\implies]$ +\end_inset + + +\end_layout + +\end_inset + +Se tiene que existen +\begin_inset Formula $\alpha_{1},\dots,\alpha_{m}$ +\end_inset + + no todos nulos con +\begin_inset Formula $\sum_{i=1}^{m}\alpha_{i}v_{i}=\alpha_{1}v_{1}+\dots+\alpha_{m}v_{m}=0$ +\end_inset + +. + Suponemos +\begin_inset Formula $\alpha_{j}\neq0$ +\end_inset + +. + Entonces +\begin_inset Formula $\alpha_{j}v_{j}=-\sum_{i=1,i\neq j}^{m}\alpha_{i}v_{i}=-\alpha_{1}v_{1}-\dots-\alpha_{j-1}v_{j-1}-\alpha_{j+1}v_{j+1}-\dots-\alpha_{m}v_{m}$ +\end_inset + +, por lo que +\begin_inset Formula $v_{j}=-\sum_{i=1,i\neq j}^{m}(\alpha_{j}^{-1}\alpha_{i}v_{i})$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\impliedby]$ +\end_inset + + +\end_layout + +\end_inset + +Si +\begin_inset Formula $v_{j}$ +\end_inset + + es combinación lineal de +\begin_inset Formula $\{v_{i}\}_{1\leq i\leq m}$ +\end_inset + +, existen escalares +\begin_inset Formula $\alpha_{1},\dots,\alpha_{j-1},\alpha_{j+1},\dots,\alpha_{m}$ +\end_inset + + tales que +\begin_inset Formula $v_{j}=\alpha_{1}v_{1}\dots,\alpha_{j-1}v_{j-1}+\alpha_{j+1}v_{j+1}+\dots+\alpha_{m}v_{m}=\sum_{i=1,i\neq j}^{m}\alpha_{i}v_{i}$ +\end_inset + +, de modo que +\begin_inset Formula $0=\alpha_{1}v_{1}+\dots+\alpha_{j-1}v_{j-1}+(-1)v_{j}+\alpha_{j+1}v_{j+1}+\dots+\alpha_{m}v_{m}$ +\end_inset + +. +\end_layout + +\begin_layout Section +Bases. + Dimensión +\end_layout + +\begin_layout Standard +Una +\series bold +base +\series default + de un espacio vectorial es un sistema de generadores linealmente independiente. + Así, +\begin_inset Formula $\{1\}$ +\end_inset + + es base de +\begin_inset Formula $K_{K}$ +\end_inset + +, +\begin_inset Formula $\{(1,0,\dots,0),(0,1,0,\dots,0),\dots,(0,0,\dots,0,1)\}$ +\end_inset + + es +\series bold +base canónica +\series default + de +\begin_inset Formula $K^{n}$ +\end_inset + + y +\begin_inset Formula $\{1,X,\dots,X^{n},\dots\}$ +\end_inset + + lo es de +\begin_inset Formula $\mathbb{R}[X]$ +\end_inset + +. + Si llamamos +\begin_inset Formula $A_{ij}\in M_{m,n}(K)$ +\end_inset + + a la matriz con un 1 en el lugar +\begin_inset Formula $ij$ +\end_inset + + y 0 en el resto, entonces +\begin_inset Formula $\{A_{ij}:1\leq i\leq m,1\leq j\leq n\}$ +\end_inset + + es base de +\begin_inset Formula $M_{m,n}(K)$ +\end_inset + +. +\end_layout + +\begin_layout Standard +\begin_inset Formula ${\cal B}$ +\end_inset + + es base de +\begin_inset Formula $V$ +\end_inset + + si y sólo si todo +\begin_inset Formula $v\in V$ +\end_inset + + se expresa de modo único como combinación lineal de +\begin_inset Formula ${\cal B}$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\implies]$ +\end_inset + + +\end_layout + +\end_inset + +Como +\begin_inset Formula ${\cal B}$ +\end_inset + + es base, es sistema de generadores, por lo que todo vector de +\begin_inset Formula $V$ +\end_inset + + es combinación lineal de vectores de +\begin_inset Formula ${\cal B}$ +\end_inset + +. + Ahora, sea +\begin_inset Formula $v=\sum_{i=1}^{n}\alpha_{i}v_{i}=\sum_{i=1}^{n}\beta_{i}v_{i}$ +\end_inset + +. + Entonces +\begin_inset Formula $0=(\alpha_{1}v_{1}+\dots+\alpha_{n}v_{n})-(\beta_{1}v_{1}+\dots+\beta_{n}v_{n})$ +\end_inset + +. + Entonces +\begin_inset Formula $0=(\alpha_{1}-\beta_{1})v_{1}+\dots+(\alpha_{n}-\beta_{n})v_{n}$ +\end_inset + +, y como +\begin_inset Formula ${\cal B}$ +\end_inset + + es linealmente independiente, se tiene que +\begin_inset Formula $\alpha_{1}-\beta_{1}=\dots=\alpha_{n}-\beta_{n}=0$ +\end_inset + + y por tanto +\begin_inset Formula $v$ +\end_inset + + se expresa de modo único. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\impliedby]$ +\end_inset + + +\end_layout + +\end_inset + + +\begin_inset Formula ${\cal B}$ +\end_inset + + es entonces sistema de generadores y queda demostrar que es linealmente + dependiente. + Sean +\begin_inset Formula $v_{1},\dots,v_{m}\in{\cal B}$ +\end_inset + +, como el 0 se representa de modo único, se tiene que si +\begin_inset Formula $\alpha_{1}v_{1}+\dots+\alpha_{m}v_{m}=0=0v_{1}+\dots+0v_{m}$ +\end_inset + + entonces +\begin_inset Formula $\alpha_{1}=\dots=\alpha_{m}=0$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $S=\{v_{1},v_{2},\dots,v_{m}\}$ +\end_inset + + es un conjunto linealmente independiente y +\begin_inset Formula $u\notin<S>$ +\end_inset + +, entonces +\begin_inset Formula $S\cup\{u\}$ +\end_inset + + es linealmente independiente. + +\series bold +Demostración: +\series default + Supongamos +\begin_inset Formula $\alpha_{1},\dots,\alpha_{m},\beta$ +\end_inset + + tales que +\begin_inset Formula $\alpha_{1}v_{1}+\dots+\alpha_{m}v_{m}+\beta u=0$ +\end_inset + +. + Si +\begin_inset Formula $\beta\neq0$ +\end_inset + + entonces +\begin_inset Formula $\beta u=-(\alpha v_{1}+\dots+\alpha_{m}v_{m})$ +\end_inset + +, de donde +\begin_inset Formula $u=-\beta^{-1}\alpha_{1}v_{1}-\dots-\beta^{-1}\alpha_{m}v_{m}$ +\end_inset + + y por tanto +\begin_inset Formula $u\in<S>$ +\end_inset + + +\begin_inset Formula $\#$ +\end_inset + +. + Por tanto +\begin_inset Formula $\beta=0$ +\end_inset + +, pero entonces +\begin_inset Formula $\alpha_{1}v_{1}+\dots+\alpha_{m}v_{m}=0$ +\end_inset + +, de donde +\begin_inset Formula $\alpha_{1}=\dots=\alpha_{m}=0$ +\end_inset + +, por lo que +\begin_inset Formula $S\cup\{u\}$ +\end_inset + + es linealmente independiente. +\end_layout + +\begin_layout Standard + +\series bold +Teorema: +\series default + Todo espacio vectorial +\begin_inset Formula $V\neq\{0\}$ +\end_inset + + tiene una base. + +\series bold +Demostración +\series default + para espacios finitamente generados. + Sea +\begin_inset Formula $V=<u_{1},\dots,u_{m}>$ +\end_inset + + y +\begin_inset Formula ${\cal A}$ +\end_inset + + el conjunto de subconjuntos +\begin_inset Formula ${\cal L}\subseteq\{u_{1},\dots,u_{m}\}$ +\end_inset + + linealmente independientes. + Sabemos que +\begin_inset Formula ${\cal A}\neq\emptyset$ +\end_inset + + porque como +\begin_inset Formula $V\neq\{0\}$ +\end_inset + + existe un +\begin_inset Formula $u_{i_{0}}\neq0$ +\end_inset + +, de modo que +\begin_inset Formula $\{u_{i_{0}}\}$ +\end_inset + + es linealmente independiente. + Sea +\begin_inset Formula ${\cal B}=\{v_{1},\dots,v_{n}\}\in{\cal A}$ +\end_inset + + un elemento de +\begin_inset Formula ${\cal A}$ +\end_inset + + con un máximo de vectores, entonces +\begin_inset Formula ${\cal B}$ +\end_inset + + es base de +\begin_inset Formula $V$ +\end_inset + + si es sistema de generadores de +\begin_inset Formula $V$ +\end_inset + +. + Sea +\begin_inset Formula $u_{i}$ +\end_inset + + un elemento del conjunto de generadores de +\begin_inset Formula $V$ +\end_inset + +. + Si +\begin_inset Formula $u_{i}\in{\cal B}$ +\end_inset + +, entonces +\begin_inset Formula $u_{i}\in<{\cal B}>$ +\end_inset + +. + Si no, entonces +\begin_inset Formula ${\cal B}\cup\{u_{i}\}\subseteq\{u_{1},\dots,u_{m}\}$ +\end_inset + + tiene un elemento más que +\begin_inset Formula ${\cal B}$ +\end_inset + +, que es un elemento de +\begin_inset Formula ${\cal A}$ +\end_inset + + con el número máximo de vectores, por lo que +\begin_inset Formula ${\cal B}\cup\{u_{i}\}\notin{\cal A}$ +\end_inset + + y será linealmente de +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +pen +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +dien +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +te, pero entonces +\begin_inset Formula $u_{i}\in<{\cal B}>$ +\end_inset + + +\begin_inset Formula $\#$ +\end_inset + +. + Acabamos de probar que +\begin_inset Formula $\{u_{1},\dots,u_{m}\}\subseteq<{\cal B}>$ +\end_inset + +, por lo que +\begin_inset Formula $V=<u_{1},\dots,u_{m}>\subseteq<{\cal B}>\subseteq V$ +\end_inset + +, por lo que +\begin_inset Formula $<{\cal B}>=V$ +\end_inset + + y ya hemos demostrado que +\begin_inset Formula ${\cal B}$ +\end_inset + + es base de +\begin_inset Formula $V$ +\end_inset + +. +\end_layout + +\begin_layout Standard + +\series bold +Teorema de Steinitz: +\series default + Si +\begin_inset Formula $\{u_{1},\dots,u_{n}\}$ +\end_inset + + es base de +\begin_inset Formula $V$ +\end_inset + + y +\begin_inset Formula $\{v_{1},\dots,v_{m}\}$ +\end_inset + + es un conjunto li +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +ne +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +al +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +men +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +te independiente, entonces se pueden sustituir +\begin_inset Formula $m$ +\end_inset + + vectores de +\begin_inset Formula $\{u_{1},\dots,u_{n}\}$ +\end_inset + + por los vectores +\begin_inset Formula $\{v_{1},\dots,v_{m}\}$ +\end_inset + + y obtener una nueva base de +\begin_inset Formula $V$ +\end_inset + +. + Entonces +\begin_inset Formula $m\le n$ +\end_inset + +. + +\series bold +Demostración: +\series default + Vemos que, como +\begin_inset Formula $\{v_{1},\dots,v_{m}\}$ +\end_inset + + es linealmente independiente, entonces +\begin_inset Formula $v_{1}\neq0$ +\end_inset + +, y tenemos que +\begin_inset Formula $v_{1}=\alpha_{1}u_{1}+\dots+a_{n}u_{n}$ +\end_inset + + con algún +\begin_inset Formula $\alpha_{i}\neq0$ +\end_inset + +. + Podemos suponer que +\begin_inset Formula $\alpha_{1}\neq0$ +\end_inset + +, y queremos probar que +\begin_inset Formula $\{v_{1},u_{2},\dots,u_{n}\}$ +\end_inset + + es base. + Primero probamos que es sistema de generadores: +\begin_inset Formula $\alpha_{1}u_{1}=v_{1}-\alpha_{2}u_{2}-\dots-\alpha_{n}u_{n}$ +\end_inset + +, por lo que +\begin_inset Formula $u_{1}=\alpha_{1}^{-1}v_{1}-\alpha_{1}^{-1}\alpha_{2}u_{2}-\dots-\alpha_{1}^{-1}\alpha_{n}u_{n}$ +\end_inset + +, de modo que +\begin_inset Formula $u_{1}$ +\end_inset + + es combinación lineal de +\begin_inset Formula $\{v_{1},u_{2},\dots,u_{n}\}$ +\end_inset + + y +\begin_inset Formula $<v_{1},u_{2},\dots,u_{n}>$ +\end_inset + + contiene un sistema de generadores, por lo que +\begin_inset Formula $\{v_{1},u_{2},\dots,u_{n}\}$ +\end_inset + + también lo es. + Ahora bien, sean +\begin_inset Formula $\beta_{1},\dots,\beta_{n}$ +\end_inset + + tales que +\begin_inset Formula $\beta_{1}v_{1}+\dots+\beta_{n}u_{n}=0$ +\end_inset + +. + Entonces +\begin_inset Formula +\begin{eqnarray*} +0 & = & \beta_{1}v_{1}+\dots+\beta_{n}u_{n}\\ + & = & \beta_{1}(\alpha_{1}u_{1}+\dots+\alpha_{n}u_{n})+\beta_{2}u_{2}+\dots+\beta_{n}u_{n}\\ + & = & \beta_{1}\alpha_{1}u_{1}+(\beta_{1}\alpha_{1}+\beta_{2})u_{2}+\dots+(\beta_{1}\alpha_{n}+\beta_{n})u_{n} +\end{eqnarray*} + +\end_inset + +Por tanto, como +\begin_inset Formula $\alpha_{1}\neq0$ +\end_inset + +, entonces +\begin_inset Formula $\beta_{1}=0$ +\end_inset + + y por tanto +\begin_inset Formula $\beta_{2}=\dots=\beta_{n}=0$ +\end_inset + + y el nuevo conjunto es también linealmente independiente. + De aquí además podemos concluir que todo conjunto de vectores linealmente + independiente de un espacio vectorial puede completarse a una base (añadiendo + vectores fuera del subespacio generado por este conjunto). +\end_layout + +\begin_layout Standard + +\series bold +Teorema: +\series default + Todas las bases de un espacio vectorial no nulo tienen el mismo número + de elementos. + +\series bold +Demostración: +\series default + Sean +\begin_inset Formula $\{u_{1},\dots,u_{n}\}$ +\end_inset + + y +\begin_inset Formula $\{v_{1},\dots,v_{m}\}$ +\end_inset + + bases de +\begin_inset Formula $V$ +\end_inset + +. + Como +\begin_inset Formula $\{v_{1},\dots,v_{m}\}$ +\end_inset + + es linealmente independiente, por el teorema de Steinitz tenemos que +\begin_inset Formula $m\leq n$ +\end_inset + +. + Análogamente, como +\begin_inset Formula $\{u_{1},\dots,u_{n}\}$ +\end_inset + + también lo es, entonces +\begin_inset Formula $n\leq m$ +\end_inset + +, por lo que +\begin_inset Formula $m=n$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Definimos la +\series bold +dimensión +\series default + de +\begin_inset Formula $V$ +\end_inset + + ( +\begin_inset Formula $\dim_{K}(V)$ +\end_inset + + o +\begin_inset Formula $\dim(V)$ +\end_inset + +) como el número de elementos de cualquier base de +\begin_inset Formula $V$ +\end_inset + +. + Si +\begin_inset Formula $V=\{0\}$ +\end_inset + +, entonces +\begin_inset Formula $\dim(V)=0$ +\end_inset + +. + Si +\begin_inset Formula $V$ +\end_inset + + no es finitamente generado, entonces +\begin_inset Formula $\dim_{K}(V)=\infty$ +\end_inset + +. + Por ejemplo, +\begin_inset Formula $\dim_{K}(K)=1$ +\end_inset + +, +\begin_inset Formula $\dim_{K}(K^{n})=n$ +\end_inset + +, +\begin_inset Formula $\dim(M_{m,n}(K))=mn$ +\end_inset + + y +\begin_inset Formula $\dim(\mathbb{R}[X])=\infty$ +\end_inset + +. +\end_layout + +\begin_layout Standard + +\series bold +Teorema: +\series default + Si +\begin_inset Formula $\dim(V)=n$ +\end_inset + + entonces: +\end_layout + +\begin_layout Enumerate +Todo conjunto linealmente independiente de +\begin_inset Formula $n$ +\end_inset + + vectores es una base. +\begin_inset Newline newline +\end_inset + +Consecuencia del teorema de Steinitz. +\end_layout + +\begin_layout Enumerate +Todo conjunto de generadores de +\begin_inset Formula $n$ +\end_inset + + vectores es una base. +\begin_inset Newline newline +\end_inset + +Siempre va a haber una base contenida en él y que va a tener +\begin_inset Formula $n$ +\end_inset + + vectores. +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $U\neq\emptyset$ +\end_inset + + es un subespacio vectorial de +\begin_inset Formula $V$ +\end_inset + + entonces +\begin_inset Formula $\dim(U)\leq n$ +\end_inset + + y además +\begin_inset Formula $\dim(U)=n\iff U=V$ +\end_inset + +. +\series bold + +\begin_inset Newline newline +\end_inset + + +\series default +Si +\begin_inset Formula ${\cal B}'$ +\end_inset + + es base de +\begin_inset Formula $U$ +\end_inset + + entonces es un conjunto de vectores de +\begin_inset Formula $V$ +\end_inset + + linealmente independiente y tiene como máximo +\begin_inset Formula $n$ +\end_inset + + elementos, por lo que +\begin_inset Formula $\dim(U)\leq\dim(V)$ +\end_inset + +. + Además, si +\begin_inset Formula $\dim(U)=\dim(V)$ +\end_inset + + entonces +\begin_inset Formula ${\cal B}'$ +\end_inset + + tiene +\begin_inset Formula $n$ +\end_inset + + elementos y, por la primera propiedad, también es base de +\begin_inset Formula $V$ +\end_inset + +, de modo que +\begin_inset Formula $U=<{\cal B}'>=V$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Definimos el +\series bold +rango +\series default + de un conjunto de vectores como +\begin_inset Formula +\[ +\text{rang}(\{u_{1},\dots,u_{m}\})=\dim(<u_{1},\dots,u_{m}>) +\] + +\end_inset + +Así, si +\begin_inset Formula $\{v_{1},\dots,v_{m}\}\subseteq V$ +\end_inset + +, es fácil comprobar que: +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\text{rang}(\{v_{1},\dots,v_{i},\dots,v_{j},\dots,v_{m}\})=\text{rang}(\{v_{1},\dots,v_{j},\dots,v_{i},\dots,v_{m}\})$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\alpha\neq0\implies\text{rang}(\{v_{1},\dots v_{i},\dots,v_{m}\})=\text{rang}(\{v_{1},\dots,\alpha v_{i},\dots,v_{m}\})$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\text{rang}(\{v_{1},\dots,v_{i},\dots,v_{j},\dots,v_{m}\})=\text{rang}(\{v_{1},\dots,v_{i}+\alpha v_{j},\dots,v_{j},\dots,v_{m}\})$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Una forma de determinar el rango de un conjunto de vectores es ir haciendo + estas operaciones y eliminando posibles vectores nulos hasta encontrar + un conjunto linealmente independiente. +\end_layout + +\begin_layout Subsection +Operaciones elementales. + Matrices escalonadas. + Método Gauss-Jordan +\end_layout + +\begin_layout Standard +En una matriz +\begin_inset Formula $A\in M_{m,n}(K)$ +\end_inset + +, a intercambiar dos columnas, multiplicar una fila por un +\begin_inset Formula $0\neq\alpha\in K$ +\end_inset + + o añadir una fila a otra multiplicada por un +\begin_inset Formula $\alpha\in K$ +\end_inset + + se les llama +\series bold +operaciones elementales por filas +\series default +. + Las +\series bold +operaciones elementales por columnas +\series default + se definen de forma análoga. + Si +\begin_inset Formula $B$ +\end_inset + + es la matriz resultante de aplicar una serie de operaciones elementales + por filas a +\begin_inset Formula $A$ +\end_inset + +, entonces el subespacio de +\begin_inset Formula $K^{n}$ +\end_inset + + generado por las filas de +\begin_inset Formula $A$ +\end_inset + + es el mismo que el generado por las filas de +\begin_inset Formula $B$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Una matriz +\begin_inset Formula $A=(a_{ij})\in M_{m,n}(K)$ +\end_inset + + está en forma +\series bold +escalonada por filas +\series default + si las filas nulas, de haberlas, son las últimas, el primer elemento no + nulo de cada fila no nula es un 1 (llamado +\series bold +pivote +\series default +) y el pivote de cada fila no nula está en una columna posterior a la de + cada uno de los pivotes anteriores. + En las matrices escalonadas por filas, las filas no nulas son linealmente + independientes. +\end_layout + +\begin_layout Standard +Si en cada columna que contenga un pivote el resto de elementos son nulos, + la matriz está en forma +\series bold +escalonada reducida por filas +\series default +\SpecialChar endofsentence + Cambiando filas por columnas tendríamos una matriz en forma +\series bold +escalonada por columnas +\series default + o +\series bold +escalonada reducida por columnas +\series default +. +\end_layout + +\begin_layout Standard + +\series bold +Método de eliminación Gauss-Jordan: +\series default + Toda matriz se puede llevar a forma escalonada (también escalonada reducida) + mediante operaciones elementales por filas. + Algoritmo: +\end_layout + +\begin_layout Enumerate +Encontrar el primer elemento +\begin_inset Formula $a$ +\end_inset + + no nulo de la primera columna no nula e intercambiar su fila con la primera. +\end_layout + +\begin_layout Enumerate +Multiplicarla por +\begin_inset Formula $a^{-1}$ +\end_inset + + para obtener un pivote. +\end_layout + +\begin_layout Enumerate +Hacer operaciones +\begin_inset Formula $Fila_{i}-cFila_{1}$ +\end_inset + +, donde +\begin_inset Formula $c$ +\end_inset + + es el elemento de cada fila debajo del pivote. +\end_layout + +\begin_layout Enumerate +Repetir el proceso con la matriz resultado de eliminar la primera fila hasta + terminar la matriz. +\end_layout + +\begin_layout Enumerate +Para obtener la escalonada reducida, hacer operaciones +\begin_inset Formula $Fila_{i}-cFila_{k}$ +\end_inset + +, donde +\begin_inset Formula $i<k$ +\end_inset + + y +\begin_inset Formula $c$ +\end_inset + + es el elemento encima del pivote de la fila +\begin_inset Formula $i$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Para obtener la base de un subespacio +\begin_inset Formula $K^{n}$ +\end_inset + + generado por +\begin_inset Formula $m$ +\end_inset + + vectores, escalonamos la matriz +\begin_inset Formula $m\times n$ +\end_inset + + cuyas filas son los vectores generadores del subespacio, y los vectores + correspondientes a filas no nulas forman una base. + Los vectores fila de cada nueva matriz son combinaciones lineales de los + iniciales. + Para obtener los coeficientes de estas combinaciones, anexamos la matriz + identidad a la derecha de la original, separada por una línea, y le aplicamos + también las operaciones, sin considerar estos coeficientes como parte de + la matriz a escalonar. +\end_layout + +\begin_layout Section +Coordenadas. + Cambio de base +\end_layout + +\begin_layout Standard +Las +\series bold +coordenadas +\series default + de un vector +\begin_inset Formula $v\in V$ +\end_inset + + respecto a la base +\begin_inset Formula ${\cal B}=\{u_{1},\dots,u_{n}\}$ +\end_inset + + son la única +\begin_inset Formula $n$ +\end_inset + +-upla +\begin_inset Formula $[v]_{{\cal B}}=(x_{1},\dots,x_{n})\in K^{n}$ +\end_inset + + con +\begin_inset Formula $v=x_{1}u_{1}+\dots+x_{n}u_{n}$ +\end_inset + +, de forma que dos vectores de +\begin_inset Formula $V$ +\end_inset + + son iguales si y solo si tienen las mismas coordenadas respecto a una base + +\begin_inset Formula ${\cal B}$ +\end_inset + +, y operar con vectores en +\begin_inset Formula $V$ +\end_inset + + es equivalente a operar en +\begin_inset Formula $K^{n}$ +\end_inset + + con las +\begin_inset Formula $n$ +\end_inset + +-uplas de sus coordenadas, pues +\begin_inset Formula $[v+v']_{{\cal B}}=(x_{1}+x'_{1},\dots,x_{n}+x'_{n})=[v]_{{\cal B}}+[v']_{{\cal B}}$ +\end_inset + + y +\begin_inset Formula $[rv]_{{\cal B}}=(rx_{1},\dots,rx_{n})=r[v]_{{\cal B}}$ +\end_inset + +. +\end_layout + +\begin_layout Subsection +Cambio de coordenadas +\end_layout + +\begin_layout Standard +Sean +\begin_inset Formula ${\cal B}=\{u_{1},\dots,u_{n}\}$ +\end_inset + + y +\begin_inset Formula ${\cal B}'=\{u'_{1},\dots,u'_{n}\}$ +\end_inset + + bases de +\begin_inset Formula $V$ +\end_inset + +, y llamamos +\begin_inset Formula $[u'_{j}]_{{\cal B}}=(p_{1j},\dots,p_{nj})$ +\end_inset + +, de forma que +\begin_inset Formula $u'_{j}=\sum_{i=1}^{n}p_{ij}u_{i}$ +\end_inset + +. + Si +\begin_inset Formula $[v]_{{\cal B}'}=(x'_{1},\dots,x'_{n})$ +\end_inset + +, entonces +\begin_inset Formula +\[ +v=x'_{1}u'_{1}+\dots+x'_{n}u'_{n}=\sum_{j=1}^{n}x'_{j}u'_{j}=\sum_{j=1}^{n}x'_{j}\left(\sum_{i=1}^{n}p_{ij}u_{i}\right)=\sum_{j=1}^{n}\sum_{i=1}^{n}x'_{j}p_{ij}u_{i}=\sum_{i=1}^{n}\left(\sum_{j=1}^{n}x'_{j}p_{ij}\right)u_{i} +\] + +\end_inset + +De forma que si +\begin_inset Formula $[v]_{{\cal B}}=(x_{1},\dots,x_{n})$ +\end_inset + +, entonces +\begin_inset Formula $x_{i}=\sum_{j=1}^{n}x'_{j}p_{ij}$ +\end_inset + +. + A las ecuaciones +\begin_inset Formula +\[ +\left.\begin{array}{ccccccc} +x_{1} & = & p_{11}x'_{1} & + & \dots & + & p_{1n}x'_{n}\\ + & \vdots\\ +x_{n} & = & p_{n1}x'_{1} & + & \dots & + & p_{nn}x'_{n} +\end{array}\right\} +\] + +\end_inset + +las llamamos +\series bold +ecuaciones del cambio de base de +\begin_inset Formula ${\cal B}'$ +\end_inset + + a +\begin_inset Formula ${\cal B}$ +\end_inset + +. +\end_layout + +\begin_layout Section +Producto de matrices +\end_layout + +\begin_layout Standard +Sean +\begin_inset Formula $A=(a_{ij})\in M_{m,n}(K)$ +\end_inset + + y +\begin_inset Formula $B=(b_{ij})\in M_{n,p}(K)$ +\end_inset + +, definimos +\begin_inset Formula $AB=(c_{ij})\in M_{m,p}(K)$ +\end_inset + + tal que +\begin_inset Formula $c_{ij}=\sum_{k=1}^{n}a_{ik}b_{kj}$ +\end_inset + +. + En general no es conmutativo, aun si ambos productos se pueden efectuar + y fuesen matrices del mismo tamaño. + Propiedades: +\end_layout + +\begin_layout Enumerate + +\series bold +Asociativa: +\series default + +\begin_inset Formula $(AB)C=A(BC)$ +\end_inset + +. +\begin_inset Formula +\[ +\begin{array}{c} +((AB)C)_{ij}=\sum_{k=1}^{p}(AB)_{ik}C_{kj}=\sum_{k=1}^{p}\sum_{l=1}^{n}A_{il}B_{lk}C_{kj}=\sum_{l=1}^{n}\sum_{k=1}^{p}A_{il}B_{lk}C_{kj}=\\ +=\sum_{l=1}^{n}A_{il}\left(\sum_{k=1}^{p}B_{lk}C_{kj}\right)=\sum_{l=1}^{n}A_{il}(BC)_{lj}=(A(BC))_{ij} +\end{array} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate + +\series bold +Distributiva respecto de la suma: +\series default + +\begin_inset Formula $A(B+C)=AB+AC$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +La +\series bold +matriz identidad +\series default +, +\begin_inset Formula $I_{n}=(\delta_{ij})$ +\end_inset + + con +\begin_inset Formula $\delta_{ii}=1$ +\end_inset + + y +\begin_inset Formula $\delta_{ij}=0$ +\end_inset + + si +\begin_inset Formula $i\neq j$ +\end_inset + +, satisface +\begin_inset Formula $AI_{n}=A$ +\end_inset + + y +\begin_inset Formula $I_{n}B=B$ +\end_inset + + para cada +\begin_inset Formula $A\in M_{m,n}(K)$ +\end_inset + + y +\begin_inset Formula $B\in M_{n,m}(K)$ +\end_inset + +. +\begin_inset Formula +\[ +C_{ij}=\sum_{k=1}^{n}A_{ik}\delta_{kj}\underset{\text{(el resto son \ensuremath{=0})}}{=}A_{ij}\delta_{jj}=A_{ij} +\] + +\end_inset + +La demostración de que +\begin_inset Formula $I_{n}B=B$ +\end_inset + + es análoga. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\alpha(AB)=(\alpha A)B=A(\alpha B)$ +\end_inset + +. +\end_layout + +\begin_layout Standard +\begin_inset Formula $A\in M_{n}(K)$ +\end_inset + + es +\series bold +invertible +\series default + si existe +\begin_inset Formula $B\in M_{n}(K)$ +\end_inset + + tal que +\begin_inset Formula $AB=BA=I_{n}$ +\end_inset + +. + Entonces +\begin_inset Formula $B$ +\end_inset + + es la +\series bold +matriz inversa +\series default + de +\begin_inset Formula $A$ +\end_inset + + y se representa +\begin_inset Formula $A^{-1}$ +\end_inset + +. + Supongamos que +\begin_inset Formula $B$ +\end_inset + + y +\begin_inset Formula $C$ +\end_inset + + son inversas de +\begin_inset Formula $A$ +\end_inset + +. + Entonces +\begin_inset Formula $C=CI_{n}=C(AB)=(CA)B=I_{n}B=B$ +\end_inset + +, por lo que la inversa es única. +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $A,B\in M_{n}(K)$ +\end_inset + + son invertibles, entonces +\begin_inset Formula $AB$ +\end_inset + + es también invertible, y +\begin_inset Formula $(AB)^{-1}=B^{-1}A^{-1}$ +\end_inset + +: +\begin_inset Formula +\[ +(B^{-1}A^{-1})(AB)=B^{-1}(A^{-1}A)B=B^{-1}I_{n}B=B^{-1}B=I_{n} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Las ecuaciones de cambio de base se pueden expresar como +\begin_inset Formula +\[ +\left(\begin{array}{c} +x_{1}\\ +x_{2}\\ +\vdots\\ +x_{n} +\end{array}\right)=\left(\begin{array}{cccc} +p_{11} & p_{12} & \cdots & p_{1n}\\ +p_{21} & p_{22} & \cdots & p_{2n}\\ +\vdots & \vdots & \ddots & \vdots\\ +p_{n1} & p_{n2} & \cdots & p_{nn} +\end{array}\right)\left(\begin{array}{c} +x'_{1}\\ +x'_{2}\\ +\vdots\\ +x'_{n} +\end{array}\right) +\] + +\end_inset + +donde las columnas de +\begin_inset Formula $(p_{ij})$ +\end_inset + + son los vectores de +\begin_inset Formula ${\cal B}'$ +\end_inset + + respecto a +\begin_inset Formula ${\cal B}$ +\end_inset + +. + Abreviadamente, +\begin_inset Formula $X_{{\cal B}}=M_{{\cal B}{\cal B}'}X'_{{\cal B}'}$ +\end_inset + +, donde a +\begin_inset Formula $M_{{\cal B}{\cal B}'}$ +\end_inset + + la llamamos +\series bold +matriz de cambio de base +\series default + de +\begin_inset Formula ${\cal B}'$ +\end_inset + + a +\begin_inset Formula ${\cal B}$ +\end_inset + +. + Podemos deducir que +\begin_inset Formula $M_{{\cal B}{\cal B}}=I_{n}$ +\end_inset + +, +\begin_inset Formula $M_{{\cal B}''{\cal B}}=M_{{\cal B}''{\cal B}'}M_{{\cal B}'{\cal B}}$ +\end_inset + + y por tanto +\begin_inset Formula $M_{{\cal B}'{\cal B}}M_{{\cal B}{\cal B}'}=M_{{\cal B}{\cal B}'}M_{{\cal B}'{\cal B}}=I_{n}$ +\end_inset + +. + Así, toda matriz de cambio de base es invertible, y viceversa. +\begin_inset Note Note +status open + +\begin_layout Plain Layout +¿Buscar la demostración de que si es invertible también es de cambio de + base? +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Section +Operaciones con subespacios +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $\{U_{i}\}_{i\in I}\neq\emptyset$ +\end_inset + + es un conjunto de subespacios vectoriales de +\begin_inset Formula $V$ +\end_inset + +, entonces +\begin_inset Formula $\bigcap_{i\in I}U_{i}$ +\end_inset + + también es subespacio vectorial de +\begin_inset Formula $V$ +\end_inset + +, pero en general +\begin_inset Formula $\bigcup_{i\in I}U_{i}$ +\end_inset + + no es subespacio vectorial. + Llamamos +\series bold +suma +\series default + de +\begin_inset Formula $U_{1}$ +\end_inset + + y +\begin_inset Formula $U_{2}$ +\end_inset + + al subespacio +\begin_inset Formula +\[ +U_{1}+U_{2}=\{u_{1}+u_{2}|u_{1}\in U_{1},u_{2}\in U_{2}\} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Este es el menor subespacio vectorial +\begin_inset Formula $V$ +\end_inset + + que contiene a +\begin_inset Formula $U_{1}$ +\end_inset + + y +\begin_inset Formula $U_{2}$ +\end_inset + +. + +\series bold +Demostración: +\series default + Si +\begin_inset Formula $u\in U_{1}$ +\end_inset + +, como +\begin_inset Formula $0\in U_{2}$ +\end_inset + +, se tiene que +\begin_inset Formula $u=u+0\in U_{1}+U_{2}$ +\end_inset + +, y viceversa, de modo que +\begin_inset Formula $U_{1}\cup U_{2}\subseteq U_{1}+U_{2}$ +\end_inset + + y además +\begin_inset Formula $U_{1}+U_{2}\neq\emptyset$ +\end_inset + +. + Demostraremos ahora que es un espacio vectorial. + Si +\begin_inset Formula $v,v'\in U_{1}+U_{2}$ +\end_inset + +, existirán +\begin_inset Formula $u_{1},u'_{1}\in U$ +\end_inset + + y +\begin_inset Formula $u_{2},u'_{2}\in U_{2}$ +\end_inset + + con +\begin_inset Formula $v=u_{1}+u_{2}$ +\end_inset + + y +\begin_inset Formula $v'=u'_{1}+u'_{2}$ +\end_inset + +, y si +\begin_inset Formula $\alpha,\alpha'\in K$ +\end_inset + +, se tiene que +\begin_inset Formula +\[ +\alpha v+\alpha'v'=\alpha u_{1}+\alpha u_{2}+\alpha'u'_{1}+\alpha'u'_{2}=(\alpha u_{1}+\alpha'u'_{1})+(\alpha u_{2}+\alpha'u'_{2})\in U_{1}+U_{2} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +La +\series bold +fórmula de Grassmann +\series default + o +\series bold +teorema de Grassman +\series default + nos dice que si +\begin_inset Formula $U_{1}$ +\end_inset + + y +\begin_inset Formula $U_{2}$ +\end_inset + + son subespacios de +\begin_inset Formula $V$ +\end_inset + +, y +\begin_inset Formula $V$ +\end_inset + + tiene dimensión finita, entonces +\begin_inset Formula +\[ +\dim(U_{1})+\dim(U_{2})=\dim(U_{1}\cap U_{2})+\dim(U_{1}+U_{2}) +\] + +\end_inset + + +\end_layout + +\begin_layout Standard + +\series bold +Demostración. + +\series default + Sea +\begin_inset Formula $\{u_{1},\dots,u_{t}\}$ +\end_inset + + base de +\begin_inset Formula $U_{1}\cap U_{2}$ +\end_inset + +, que completamos por un lado a la base +\begin_inset Formula $\{u_{1},\dots,u_{t},u_{t+1},\dots,u_{r}\}$ +\end_inset + + de +\begin_inset Formula $U_{1}$ +\end_inset + + y por otro a la base +\begin_inset Formula $\{u_{1},\dots,u_{t},v_{t+1},\dots,v_{s}\}$ +\end_inset + + de +\begin_inset Formula $U_{2}$ +\end_inset + +. + Entonces +\begin_inset Formula $\{u_{1},\dots,u_{t},u_{t+1},\dots,u_{r},v_{t+1},\dots,v_{s}\}$ +\end_inset + + es sistema de generadores de +\begin_inset Formula $U_{1}+U_{2}$ +\end_inset + +. + Queda ver que es además linealmente independiente. +\end_layout + +\begin_layout Standard +Supongamos +\begin_inset Formula $\alpha_{1}u_{1}+\dots+\alpha_{t}u_{t}+\alpha_{t+1}u_{t+1}+\dots+\alpha_{r}u_{r}+\beta_{t+1}v_{t+1}+\dots+\beta_{s}v_{s}=0$ +\end_inset + +. + Entonces +\begin_inset Formula $\alpha_{1}u_{1}+\dots+\alpha_{r}u_{r}=-\beta_{t+1}v_{t+1}-\dots-\beta_{s}v_{s}\in U_{1}\cap U_{2}$ +\end_inset + +. + Pero como +\begin_inset Formula $\{u_{1},\dots,u_{t}\}$ +\end_inset + + es base de +\begin_inset Formula $U_{1}\cap U_{2}$ +\end_inset + +, se tiene que +\begin_inset Formula $-\beta_{t+1}v_{t+1}-\dots-\beta_{s}v_{s}=\gamma_{1}u_{1}+\dots+\gamma_{t}u_{t}$ +\end_inset + +, por lo que +\begin_inset Formula $\gamma_{1}u_{1}+\dots+\gamma_{t}u_{t}+\beta_{t+1}v_{t+1}+\dots+\beta_{s}v_{s}=0$ +\end_inset + +. + Al ser +\begin_inset Formula $\{u_{1},\dots,u_{t},v_{t+1},\dots,v_{s}\}$ +\end_inset + + base de +\begin_inset Formula $U_{2}$ +\end_inset + +, se tiene que +\begin_inset Formula $\beta_{t+1}=\dots=\beta_{s}=0$ +\end_inset + +, por lo que +\begin_inset Formula $\alpha_{1}u_{1}+\dots+\alpha_{r}u_{r}=0$ +\end_inset + +. + Pero como +\begin_inset Formula $\{u_{1},\dots,u_{r}\}$ +\end_inset + + es base de +\begin_inset Formula $U_{1}$ +\end_inset + + se tiene que +\begin_inset Formula $\alpha_{1}=\dots=\alpha_{r}=0$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Así, se tiene que +\begin_inset Formula $\{u_{1},\dots,u_{t},u_{t+1},\dots,u_{r},v_{t+1},\dots,v_{s}\}$ +\end_inset + + es una familia linealmente independiente y por tanto una base del subespacio + +\begin_inset Formula $U_{1}+U_{2}$ +\end_inset + +, que tendrá dimensión +\begin_inset Formula $\dim(U_{1}+U_{2})=r+s-t=\dim(U_{1})+\dim(U_{2})-\dim(U_{1}\cap U_{2})$ +\end_inset + +. +\end_layout + +\begin_layout Standard +\begin_inset Formula $U_{1}$ +\end_inset + + y +\begin_inset Formula $U_{2}$ +\end_inset + + subespacios de +\begin_inset Formula $V$ +\end_inset + + están en +\series bold +suma directa +\series default + si +\begin_inset Formula $U_{1}\cap U_{2}=\{0\}$ +\end_inset + +. + Se dice entonces que +\begin_inset Formula $U_{1}+U_{2}$ +\end_inset + + es una suma directa y se representa +\begin_inset Formula $U_{1}\oplus U_{2}$ +\end_inset + +. + Por tanto +\begin_inset Formula $\dim(U_{1}\oplus U_{2})=\dim(U_{1})+\dim(U_{2})$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Una suma de subespacios +\begin_inset Formula $U_{1}+U_{2}$ +\end_inset + + es directa si y sólo si +\begin_inset Formula $\forall v\in U_{1}+U_{2},\exists!u_{1}\in U_{1},u_{2}\in U_{2}:v=u_{1}+u_{2}$ +\end_inset + +. + Llamamos a +\begin_inset Formula $u_{1}$ +\end_inset + + y +\begin_inset Formula $u_{2}$ +\end_inset + + las +\series bold +componentes +\series default + de +\begin_inset Formula $v$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\implies]$ +\end_inset + + +\end_layout + +\end_inset + +Si +\begin_inset Formula $u_{1}+u_{2}=u'_{1}+u'_{2}$ +\end_inset + + con +\begin_inset Formula $u_{1},u'_{1}\in U_{1}$ +\end_inset + + y +\begin_inset Formula $u_{2},u'_{2}\in U_{2}$ +\end_inset + +, entonces +\begin_inset Formula $u_{1}-u'_{1}=u'_{2}-u_{2}\in U_{1}\cap U_{2}$ +\end_inset + +, por lo que +\begin_inset Formula $u_{1}-u'_{1}=u'_{2}-u_{2}=0$ +\end_inset + + y +\begin_inset Formula $u_{1}=u'_{1}$ +\end_inset + + y +\begin_inset Formula $u_{2}=u'_{2}$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\impliedby]$ +\end_inset + + +\end_layout + +\end_inset + +Si +\begin_inset Formula $u\in U_{1}\cap U_{2}$ +\end_inset + +, entonces +\begin_inset Formula $u=u+0=0+u$ +\end_inset + +, pero como +\begin_inset Formula $u$ +\end_inset + + se expresa de modo único como suma de un vector de +\begin_inset Formula $U_{1}$ +\end_inset + + y otro de +\begin_inset Formula $U_{2}$ +\end_inset + +, se tiene que +\begin_inset Formula $u=0$ +\end_inset + +, y por tanto +\begin_inset Formula $U_{1}\cap U_{2}=\{0\}$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Dado +\begin_inset Formula $U$ +\end_inset + + subespacio vectorial de +\begin_inset Formula $V$ +\end_inset + + existe +\begin_inset Formula $U'$ +\end_inset + +, llamado +\series bold +complementario +\series default + de +\begin_inset Formula $U$ +\end_inset + + en +\begin_inset Formula $V$ +\end_inset + +, tal que +\begin_inset Formula $V=U\oplus U'$ +\end_inset + +, pues si expandimos la base +\begin_inset Formula $\{u_{1},\dots,u_{r}\}$ +\end_inset + + de +\begin_inset Formula $U$ +\end_inset + + a una base +\begin_inset Formula $\{u_{1},\dots,u_{r},u_{r+1},\dots,u_{n}\}$ +\end_inset + + de +\begin_inset Formula $V$ +\end_inset + + entonces +\begin_inset Formula $U'=<u_{r+1},\dots,u_{n}>$ +\end_inset + + satisface la condición. + El complementario no tiene por qué ser único. +\end_layout + +\begin_layout Standard +Una suma +\begin_inset Formula $U_{1}+\dots+U_{k}$ +\end_inset + + es suma directa si todo vector de la suma se expresa de modo único como + suma de un vector de cada +\begin_inset Formula $U_{i}$ +\end_inset + +, lo que ocurre si y sólo si +\begin_inset Formula $\forall i\in\{1,\dots,k\},U_{i}\cap(\sum_{1\leq j\leq k,j\neq i}U_{j})=\{0\}$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $u_{1},\dots,u_{k}\in V$ +\end_inset + +, entonces +\begin_inset Formula $<u_{1},\dots,u_{k}>=<u_{1}>+\dots+<u_{k}>$ +\end_inset + +. + Si además son linealmente independientes, entonces +\begin_inset Formula $<u_{1},\dots,u_{k}>=<u_{1}>\oplus\dots\oplus<u_{n}>$ +\end_inset + +. + Así, +\begin_inset Formula $\{u_{1},\dots,u_{n}\}$ +\end_inset + + es base de +\begin_inset Formula $V$ +\end_inset + + si y sólo si +\begin_inset Formula $V=<u_{1}>\oplus\dots\oplus<u_{n}>$ +\end_inset + +. +\end_layout + +\end_body +\end_document diff --git a/algl/n2.lyx b/algl/n2.lyx new file mode 100644 index 0000000..bd834d3 --- /dev/null +++ b/algl/n2.lyx @@ -0,0 +1,2102 @@ +#LyX 2.3 created this file. For more info see http://www.lyx.org/ +\lyxformat 544 +\begin_document +\begin_header +\save_transient_properties true +\origin unavailable +\textclass book +\use_default_options true +\maintain_unincluded_children false +\language spanish +\language_package default +\inputencoding auto +\fontencoding global +\font_roman "default" "default" +\font_sans "default" "default" +\font_typewriter "default" "default" +\font_math "auto" "auto" +\font_default_family default +\use_non_tex_fonts false +\font_sc false +\font_osf false +\font_sf_scale 100 100 +\font_tt_scale 100 100 +\use_microtype false +\use_dash_ligatures true +\graphics default +\default_output_format default +\output_sync 0 +\bibtex_command default +\index_command default +\paperfontsize default +\spacing single +\use_hyperref false +\papersize default +\use_geometry false +\use_package amsmath 1 +\use_package amssymb 1 +\use_package cancel 1 +\use_package esint 1 +\use_package mathdots 1 +\use_package mathtools 1 +\use_package mhchem 1 +\use_package stackrel 1 +\use_package stmaryrd 1 +\use_package undertilde 1 +\cite_engine basic +\cite_engine_type default +\biblio_style plain +\use_bibtopic false +\use_indices false +\paperorientation portrait +\suppress_date false +\justification true +\use_refstyle 1 +\use_minted 0 +\index Index +\shortcut idx +\color #008000 +\end_index +\secnumdepth 3 +\tocdepth 3 +\paragraph_separation indent +\paragraph_indentation default +\is_math_indent 0 +\math_numbering_side default +\quotes_style swiss +\dynamic_quotes 0 +\papercolumns 1 +\papersides 1 +\paperpagestyle default +\tracking_changes false +\output_changes false +\html_math_output 0 +\html_css_as_file 0 +\html_be_strict false +\end_header + +\begin_body + +\begin_layout Standard +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + + es una +\series bold +aplicación lineal +\series default + u +\series bold +homomorfismo de espacios vectoriales +\series default + si +\begin_inset Formula $f(u+u')=f(u)+f(u')\forall u,u'\in U$ +\end_inset + + y +\begin_inset Formula $f(\alpha u)=\alpha f(u)\forall\alpha\in K,u\in U$ +\end_inset + +, es decir, si +\begin_inset Formula $f(\sum\alpha_{i}u_{i})=\sum\alpha_{i}f(u_{i})$ +\end_inset + +. + Ejemplos: +\end_layout + +\begin_layout Itemize +La +\series bold +aplicación identidad: +\series default + +\begin_inset Formula $Id_{V}:V\rightarrow V$ +\end_inset + + con +\begin_inset Formula $Id_{V}(v)=v$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +La +\series bold +aplicación inclusión: +\series default + +\begin_inset Formula $i:U\subseteq V\rightarrow V$ +\end_inset + + con +\begin_inset Formula $i(u)=u$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +La +\series bold +aplicación lineal nula: +\series default + +\begin_inset Formula $0:U\rightarrow V$ +\end_inset + + con +\begin_inset Formula $0(u)=0$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +La +\series bold +homotecia de razón +\begin_inset Formula $\alpha$ +\end_inset + +: +\series default + +\begin_inset Formula $h_{\alpha}:V\rightarrow V$ +\end_inset + + con +\begin_inset Formula $h_{\alpha}(v)=\alpha v$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +Las +\series bold +proyecciones de +\begin_inset Formula $V$ +\end_inset + + sobre +\begin_inset Formula $U$ +\end_inset + + y +\begin_inset Formula $W$ +\end_inset + +, +\series default + con +\begin_inset Formula $V=U\oplus W$ +\end_inset + +: +\begin_inset Formula $p_{U}:V\rightarrow U$ +\end_inset + + y +\begin_inset Formula $p_{W}:V\rightarrow W$ +\end_inset + +, tales que si +\begin_inset Formula $v=u+w$ +\end_inset + + con +\begin_inset Formula $v\in V$ +\end_inset + +, +\begin_inset Formula $u\in U$ +\end_inset + + y +\begin_inset Formula $w\in W$ +\end_inset + +, entonces +\begin_inset Formula $p_{U}(v)=u$ +\end_inset + + y +\begin_inset Formula $p_{W}(v)=w$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +La aplicación +\begin_inset Formula $f_{A}:K^{n}\rightarrow K^{m}$ +\end_inset + + con +\begin_inset Formula $A\in M_{m,n}(K)$ +\end_inset + +, dada por +\begin_inset Formula +\[ +f_{A}(v)=A\left(\begin{array}{c} +|\\ +v\\ +| +\end{array}\right) +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Tenemos que +\begin_inset Formula $f(0_{U})=0_{V}$ +\end_inset + +, y que +\begin_inset Formula $f(-u)=-f(u)$ +\end_inset + +. + Además, si +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + + y +\begin_inset Formula $g:V\rightarrow W$ +\end_inset + + son aplicaciones lineales, +\begin_inset Formula $g\circ f:U\rightarrow W$ +\end_inset + + también lo es. +\end_layout + +\begin_layout Section +Aplicaciones lineales y subespacios. + Núcleo e Imagen +\end_layout + +\begin_layout Standard +El +\series bold +núcleo +\series default + de +\begin_inset Formula $f$ +\end_inset + + se define como +\begin_inset Formula $\text{Nuc}(f)=\ker(f)=f^{-1}(\{0\})$ +\end_inset + +, y la +\series bold +imagen +\series default + de +\begin_inset Formula $f$ +\end_inset + + como +\begin_inset Formula $\text{Im}(f)=\{f(u)\}_{u\in U}$ +\end_inset + +. + Si +\begin_inset Formula $U'\leq U$ +\end_inset + + entonces +\begin_inset Formula $f(U')\leq V$ +\end_inset + +, y si +\begin_inset Formula $V'\leq V$ +\end_inset + +, entonces +\begin_inset Formula $\text{Nuc}(f)\leq f^{-1}(V')\leq U$ +\end_inset + +. + En particular, +\begin_inset Formula $\text{Nuc}(f)$ +\end_inset + + e +\begin_inset Formula $\text{Im}(f)$ +\end_inset + + son espacios vectoriales, y si +\begin_inset Formula $U'=<u_{1},\dots,u_{r}>\leq U$ +\end_inset + +, entonces +\begin_inset Formula $f(U')=<f(u_{1}),\dots,f(u_{r})>$ +\end_inset + +. + +\series bold +Demostración: +\series default + Sean +\begin_inset Formula $u_{1},u_{2}\in U,\alpha_{1},\alpha_{2}\in K$ +\end_inset + +, y sean +\begin_inset Formula $v_{1}=f(u_{1}),v_{2}=f(u_{2})\in f(U')$ +\end_inset + +. + Entonces +\begin_inset Formula $\alpha_{1}v_{1}+\alpha_{2}v_{2}=\alpha_{1}f(u_{1})+\alpha_{2}f(u_{2})=f(\alpha_{1}u_{1}+\alpha_{2}u_{2})\in f(U')$ +\end_inset + +, por lo que +\begin_inset Formula $f(U')$ +\end_inset + + es un espacio vectorial. + Ahora bien, si +\begin_inset Formula $V'$ +\end_inset + + es un subespacio de +\begin_inset Formula $V$ +\end_inset + + entonces +\begin_inset Formula $\{0\}\subseteq V'$ +\end_inset + +, por lo que +\begin_inset Formula $f^{-1}(\{0\})=\text{Nuc}(f)\subseteq f^{-1}(V')$ +\end_inset + +. + Entonces si +\begin_inset Formula $u_{1},u_{2}\in f^{-1}(V')$ +\end_inset + + y +\begin_inset Formula $\alpha_{1},\alpha_{2}\in K$ +\end_inset + +, entonces +\begin_inset Formula $f(\alpha_{1}u_{1}+\alpha_{2}u_{2})=\alpha_{1}f(u_{1})+\alpha_{2}f(u_{2})\in V'$ +\end_inset + +, y por lo tanto +\begin_inset Formula $\alpha_{1}u_{1}+\alpha_{2}u_{2}\in f^{-1}(V')$ +\end_inset + + y +\begin_inset Formula $f^{-1}(V')$ +\end_inset + + es un espacio vectorial. +\end_layout + +\begin_layout Standard + +\series bold +Teorema: +\series default + Para +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + + con +\begin_inset Formula $\dim(U)$ +\end_inset + + finita, entonces +\begin_inset Formula $\dim(U)=\dim(\text{Nuc}(f))+\dim(\text{Im}(f))$ +\end_inset + +. + +\series bold +Demostración: +\series default + Sea +\begin_inset Formula $\{v_{1},\dots,v_{n}\}$ +\end_inset + + base de +\begin_inset Formula $U$ +\end_inset + +. + Entonces +\begin_inset Formula $\text{Im}(f)=<f(v_{1}),\dots f(v_{n})>$ +\end_inset + + es de dimensión finita. + Ahora sea +\begin_inset Formula $\{v_{1},\dots,v_{k}\}$ +\end_inset + + base de +\begin_inset Formula $\text{Nuc}(f)\leq U$ +\end_inset + +, con +\begin_inset Formula $k\leq n$ +\end_inset + +. + Entonces +\begin_inset Formula $f(v_{1})=\dots=f(v_{k})=0$ +\end_inset + +, por lo que +\begin_inset Formula $\text{Im}(f)=<f(v_{1}),\dots,f(v_{k}),f(v_{k+1}),\dots,f(v_{n})>=<f(v_{k+1}),\dots,f(v_{n})>$ +\end_inset + +, por lo que +\begin_inset Formula $\{f(v_{k+1}),\dots,f(v_{n})\}$ +\end_inset + + es sistema de generadores de +\begin_inset Formula $\text{Im}(f)$ +\end_inset + +. + A continuación mostramos que es linealmente independiente. + Sea +\begin_inset Formula $0=\alpha_{k+1}f(v_{k+1})+\dots+\alpha_{n}f(v_{n})=f(\alpha_{k+1}v_{k+1}+\dots+\alpha_{n}v_{n})$ +\end_inset + +. + Entonces +\begin_inset Formula $\alpha_{k+1}v_{k+1}+\dots+\alpha_{n}v_{n}\in\text{Nuc}(f)$ +\end_inset + +, por lo que existen +\begin_inset Formula $\beta_{1},\dots,\beta_{k}$ +\end_inset + + tales que +\begin_inset Formula $\alpha_{k+1}v_{k+1}+\dots+\alpha_{n}v_{n}=\beta_{1}v_{1}+\dots+\beta_{k}v_{k}$ +\end_inset + +. + Pero entonces +\begin_inset Formula $\beta_{1}v_{1}+\dots+\beta_{k}v_{k}-\alpha_{k+1}v_{k+1}-\dots-\alpha_{n}v_{n}=0$ +\end_inset + +, y como +\begin_inset Formula $\{v_{1},\dots,v_{n}\}$ +\end_inset + + es base de +\begin_inset Formula $U$ +\end_inset + +, se tiene que +\begin_inset Formula $\beta_{1}=\dots=\beta_{k}=\alpha_{k+1}=\dots=\alpha_{n}=0$ +\end_inset + +, de modo que +\begin_inset Formula $\{v_{k+1},\dots,v_{n}\}$ +\end_inset + + es linealmente independiente y por ello +\begin_inset Formula $\{f(v_{k+1}),\dots,f(v_{n})\}$ +\end_inset + + también, por lo que es base de +\begin_inset Formula $\text{Im}(f)$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Llamamos +\series bold +rango +\series default + de +\begin_inset Formula $f$ +\end_inset + + a la dimensión de la imagen: +\begin_inset Formula $\text{rang}(f)=\dim(\text{Im}(f))$ +\end_inset + +. + Así, dada +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + + y +\begin_inset Formula $\{u_{1},\dots,u_{n}\}$ +\end_inset + + base de +\begin_inset Formula $U$ +\end_inset + +, entonces +\begin_inset Formula $f(U)=<f(u_{1}),\dots,f(u_{n})>$ +\end_inset + + y por tanto +\begin_inset Formula +\[ +\text{rang}(f)=\dim(\text{Im}(f))=\dim(<f(u_{1}),\dots,f(u_{n})>)=\text{rang}(\{f(u_{1}),\dots,f(u_{n})\}) +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + + es una aplicación lineal y +\begin_inset Formula $\dim(U)=\dim(V)<\infty$ +\end_inset + +, entonces +\begin_inset Formula +\[ +f\text{ inyectiva}\iff f\text{ suprayectiva}\iff f\text{ biyectiva}\iff\text{rang}(f)=\dim(U)\iff\text{Nuc}(f)=\{0\} +\] + +\end_inset + + +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $1\iff2\iff3]$ +\end_inset + + +\end_layout + +\end_inset + +Equivalen al hecho de que, para +\begin_inset Formula $f:A\rightarrow B$ +\end_inset + + con +\begin_inset Formula $A$ +\end_inset + + y +\begin_inset Formula $B$ +\end_inset + + conjuntos finitos, es lo mismo decir que +\begin_inset Formula $f$ +\end_inset + + sea inyectiva, suprayectiva o biyectiva. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $3\iff4]$ +\end_inset + + +\end_layout + +\end_inset + + +\begin_inset Formula $\text{rang}(f)=\dim(\text{Im}(U))\overset{\text{(supray.)}}{=}\text{dim}(V)$ +\end_inset + +. + Si +\begin_inset Formula $f$ +\end_inset + + no fuera suprayectiva, entonces +\begin_inset Formula $\dim(\text{Im}(U))<\dim(V)$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $1\implies5]$ +\end_inset + + +\end_layout + +\end_inset + + +\begin_inset Formula $u\in\text{Nuc}(f)\implies f(u)=0_{V}=f(0_{U})\implies u=0_{U}$ +\end_inset + + +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $5\implies1]$ +\end_inset + + +\end_layout + +\end_inset + + +\begin_inset Formula $\text{Nuc}(f)=\{0\}\implies\left(f(u)=f(u')\implies0=f(u-u')\implies u-u'\in\text{Nuc}(f)\implies u=u'\right)$ +\end_inset + + +\end_layout + +\begin_layout Standard +El homomorfismo +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + + es un +\series bold +isomorfismo de espacios vectoriales +\series default + si es biyectivo, un +\series bold +endomorfismo +\series default + de +\begin_inset Formula $U$ +\end_inset + + si +\begin_inset Formula $U=V$ +\end_inset + + y un +\series bold +automorfismo +\series default + es un endomorfismo biyectivo. + Ahora, dado el isomorfismo +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + +, +\begin_inset Formula $f^{-1}:V\rightarrow U$ +\end_inset + + es una aplicación lineal y por tanto un isomorfismo. + +\series bold +Demostración: +\series default + Consideramos +\begin_inset Formula $u=f^{-1}(v)$ +\end_inset + + y +\begin_inset Formula $u'=f^{-1}(v')$ +\end_inset + +. + Entonces +\begin_inset Formula $f(u+u')=f(u)+f(u')=v+v'$ +\end_inset + + y por tanto +\begin_inset Formula $f^{-1}(v+v')=u+u'=f^{-1}(v)+f^{-1}(v')$ +\end_inset + +. + Del mismo modo, +\begin_inset Formula $f(\alpha u)=\alpha f(u)=\alpha v$ +\end_inset + +, por lo que +\begin_inset Formula $f^{-1}(\alpha v)=\alpha u=\alpha f^{-1}(v)$ +\end_inset + +. +\end_layout + +\begin_layout Standard +\begin_inset Formula $U$ +\end_inset + + y +\begin_inset Formula $V$ +\end_inset + + son +\series bold +isomorfos +\series default + ( +\begin_inset Formula $U\cong V$ +\end_inset + +) si existe un isomorfismo +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + +. + Podemos comprobar que la relación es de equivalencia, y si +\begin_inset Formula $U$ +\end_inset + + y +\begin_inset Formula $V$ +\end_inset + + son +\begin_inset Formula $K$ +\end_inset + +-espacios vectoriales, entonces +\begin_inset Formula $U\cong V\iff\dim(U)=\dim(V)$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\implies]$ +\end_inset + + +\end_layout + +\end_inset + + +\begin_inset Formula $U\cong V\implies\dim(U)=\dim(\text{Nuc}(f))+\dim(\text{Im}(f))=0+\dim(V)$ +\end_inset + + +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\impliedby]$ +\end_inset + + +\end_layout + +\end_inset + +Sean +\begin_inset Formula $f:U\rightarrow K^{n}$ +\end_inset + + y +\begin_inset Formula $g:V\rightarrow K^{n}$ +\end_inset + + isomorfismos con +\begin_inset Formula $f(u)=[u]_{{\cal B}}$ +\end_inset + + y +\begin_inset Formula $g(v)=[v]_{\beta'}$ +\end_inset + + ; entonces +\begin_inset Formula $g^{-1}\circ f:U\rightarrow V$ +\end_inset + + también es un isomorfismo. +\end_layout + +\begin_layout Section +Determinación de una aplicación lineal +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $U$ +\end_inset + + y +\begin_inset Formula $V$ +\end_inset + + son +\begin_inset Formula $K$ +\end_inset + +-espacios vectoriales con +\begin_inset Formula ${\cal B}=\{u_{1},\dots,u_{n}\}$ +\end_inset + + base de +\begin_inset Formula $U$ +\end_inset + + y +\begin_inset Formula $v_{1},\dots,v_{n}$ +\end_inset + + vectores cualesquiera de +\begin_inset Formula $V$ +\end_inset + +, existe una única +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + + con +\begin_inset Formula $f(u_{i})=v_{i}\forall i$ +\end_inset + +, pues es aquella dada por +\begin_inset Formula $f(\alpha_{1}u_{1}+\dots+\alpha_{n}u_{n})=\alpha_{1}v_{1}+\dots+\alpha_{n}v_{n}$ +\end_inset + +. + Esto también se cumple para espacios de dimensión infinita. +\end_layout + +\begin_layout Standard +También, si +\begin_inset Formula ${\cal B}=\{u_{i}\}_{i\in I}$ +\end_inset + + es base de +\begin_inset Formula $U$ +\end_inset + + (la cual puede ser infinita) y +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + + lineal entonces: +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $f$ +\end_inset + + es inyectiva si y sólo si +\begin_inset Formula $\{f(u_{i})\}_{i\in I}$ +\end_inset + + es linealmente independiente. +\end_layout + +\begin_deeper +\begin_layout Enumerate +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\implies]$ +\end_inset + + +\end_layout + +\end_inset + + +\begin_inset Formula $0=\alpha_{1}f(u_{1})+\dots+\alpha_{k}f(u_{k})=f(\alpha_{1}u_{1}+\dots+\alpha_{k}u_{k})\implies\alpha_{1}u_{1}+\dots+\alpha_{k}u_{k}\in\text{Nuc}(f)=\{0\}\implies\alpha_{1}u_{1}+\dots+\alpha_{k}u_{k}=0\implies\alpha_{1},\dots,\alpha_{k}=0$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\impliedby]$ +\end_inset + + +\end_layout + +\end_inset + +Partimos de que +\begin_inset Formula $\{f(u_{i})\}_{i\in I}$ +\end_inset + + es linealmente independiente. + Sea +\begin_inset Formula $u\in\text{Nuc}(f)$ +\end_inset + +, si +\begin_inset Formula $u=\alpha_{1}u_{1}+\dots+\alpha_{k}u_{k}$ +\end_inset + + entonces +\begin_inset Formula $0=f(u)=\alpha_{1}f(u_{1})+\dots+\alpha_{k}f(u_{k})\implies\alpha_{i}=0\forall i\implies u=0$ +\end_inset + +, por lo que entonces +\begin_inset Formula $\text{Nuc}(f)=\{0\}$ +\end_inset + +. +\end_layout + +\end_deeper +\begin_layout Enumerate +\begin_inset Formula $f$ +\end_inset + + es suprayectiva si y sólo si +\begin_inset Formula $\{f(u_{i})\}_{i\in I}$ +\end_inset + + es una familia de generadores de +\begin_inset Formula $V$ +\end_inset + +. +\begin_inset Formula +\[ +f\text{ suprayectiva}\iff f(U)=V\iff<\{f(u_{i})\}_{i\in I}>=V +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $f$ +\end_inset + + es biyectiva, y por tanto isomorfismo, si y sólo si +\begin_inset Formula $\{f(u_{i})\}_{i\in I}$ +\end_inset + + es +\begin_inset space \space{} +\end_inset + + base de +\begin_inset Formula $V$ +\end_inset + +. +\end_layout + +\begin_layout Section +Representación matricial de una aplicación lineal. + Rango de una matriz. + Matrices equivalentes +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $U$ +\end_inset + + y +\begin_inset Formula $V$ +\end_inset + + son +\begin_inset Formula $K$ +\end_inset + +-espacios vectoriales de dimensión finita, +\begin_inset Formula ${\cal B}=\{u_{1},\dots,u_{n}\}$ +\end_inset + + es base de +\begin_inset Formula $U$ +\end_inset + + y +\begin_inset Formula ${\cal B}'=\{v_{1},\dots,v_{m}\}$ +\end_inset + + base de +\begin_inset Formula $V$ +\end_inset + +, y +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + + es un homomorfismo, entonces para cada +\begin_inset Formula $j$ +\end_inset + + existirán +\begin_inset Formula $a_{ij}$ +\end_inset + + tales que +\begin_inset Formula +\[ +f(u_{j})=\sum_{i=1}^{m}a_{ij}v_{i} +\] + +\end_inset + +Así, si +\begin_inset Formula $[u]_{{\cal B}}=(x_{1},\dots,x_{n})$ +\end_inset + +, entonces +\begin_inset Formula $u=\sum_{j=1}^{n}x_{j}u_{j}\in U$ +\end_inset + + y +\begin_inset Formula +\[ +f(u)=f\left(\sum_{j=1}^{n}x_{j}u_{j}\right)=\sum_{j=1}^{n}x_{j}f(u_{j})=\sum_{j=1}^{n}x_{j}\left(\sum_{i=1}^{m}a_{ij}v_{i}\right)=\sum_{j=1}^{n}\sum_{i=1}^{m}(x_{j}a_{ij})v_{i}=\sum_{i=1}^{m}\left(\sum_{j=1}^{n}a_{ij}x_{j}\right)v_{i} +\] + +\end_inset + +por lo que +\begin_inset Formula $[f(u)]_{{\cal B}'}=(\sum_{j=1}^{n}a_{1j}x_{j},\dots,\sum_{j=1}^{n}a_{mj}x_{j})$ +\end_inset + +, de modo que, si +\begin_inset Formula $[f(u)]_{{\cal B}'}=(y_{1},\dots,y_{m})$ +\end_inset + +, entonces +\begin_inset Formula +\[ +\left(\begin{array}{c} +y_{1}\\ +\vdots\\ +y_{m} +\end{array}\right)=\left(\begin{array}{ccc} +a_{11} & \cdots & a_{1n}\\ +\vdots & \ddots & \vdots\\ +a_{m1} & \cdots & a_{mn} +\end{array}\right)\left(\begin{array}{c} +x_{1}\\ +\vdots\\ +x_{n} +\end{array}\right) +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Siendo las columnas de +\begin_inset Formula $(a_{ij})$ +\end_inset + + los +\begin_inset Formula $[f(u_{j})]_{{\cal B}'}$ +\end_inset + +, es decir, las imágenes de los elementos de +\begin_inset Formula ${\cal B}$ +\end_inset + + respecto de +\begin_inset Formula ${\cal B}'$ +\end_inset + +. + Entonces +\begin_inset Formula $[f(u)]_{{\cal B}'}=A[u]_{{\cal B}}$ +\end_inset + +, lo que se conoce como +\series bold +representación matricial de +\begin_inset Formula $f$ +\end_inset + + respecto a las bases +\begin_inset Formula ${\cal B}$ +\end_inset + + y +\begin_inset Formula ${\cal B}'$ +\end_inset + + +\series default +. + A la matriz +\begin_inset Formula $(a_{ij})$ +\end_inset + + se le llama +\series bold +matriz de +\begin_inset Formula $f$ +\end_inset + + +\series default + o +\series bold +matriz asociada a +\begin_inset Formula $f$ +\end_inset + + respecto a las bases +\begin_inset Formula ${\cal B}$ +\end_inset + + y +\begin_inset Formula ${\cal B}'$ +\end_inset + + +\series default +, y se denomina +\begin_inset Formula $M_{{\cal B}',{\cal B}}(f)$ +\end_inset + +. + Así, +\begin_inset Formula +\[ +[f(u)]_{{\cal B}'}=M_{{\cal B}',{\cal B}}(f)[u]_{{\cal B}} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Tenemos que +\begin_inset Formula $M_{{\cal B}',{\cal B}}(f)$ +\end_inset + + está completamente determinada por +\begin_inset Formula $f$ +\end_inset + +, y de igual modo, +\begin_inset Formula $f$ +\end_inset + + está univocamente determinada por +\begin_inset Formula $M_{{\cal B}',{\cal B}}(f)$ +\end_inset + +. + Además, si +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + + y +\begin_inset Formula $g:V\rightarrow W$ +\end_inset + + son aplicaciones lineales y +\begin_inset Formula ${\cal B}_{1}$ +\end_inset + +, +\begin_inset Formula ${\cal B}_{2}$ +\end_inset + + y +\begin_inset Formula ${\cal B}_{3}$ +\end_inset + + son bases respectivas de +\begin_inset Formula $U$ +\end_inset + +, +\begin_inset Formula $V$ +\end_inset + + y +\begin_inset Formula $W$ +\end_inset + +, entonces +\begin_inset Formula $M_{{\cal B}_{3},{\cal B}_{1}}(g\circ f)=M_{{\cal B}_{3},{\cal B}_{2}}(g)M_{{\cal B}_{2},{\cal B}_{1}}(f)$ +\end_inset + +. + +\series bold +Demostración: +\series default + Para cada +\begin_inset Formula $u\in U,v\in V$ +\end_inset + +, tenemos que +\begin_inset Formula $M_{{\cal B}_{2},{\cal B}_{1}}(f)[u]_{{\cal B}_{1}}=[f(u)]_{{\cal B}_{2}}$ +\end_inset + + y +\begin_inset Formula $M_{{\cal B}_{3},{\cal B}_{2}}(g)[v]_{{\cal B}_{2}}=[g(v)]_{{\cal B}_{3}}$ +\end_inset + +, por lo que +\begin_inset Formula +\[ +M_{{\cal B}_{3},{\cal B}_{2}}(g)M_{{\cal B}_{2},{\cal B}_{1}}(f)[u]_{{\cal B}_{1}}=M_{{\cal B}_{3},{\cal B}_{2}}(g)[f(u)]_{{\cal B}_{2}}=[g(f(u))]_{{\cal B}_{3}}=[(g\circ f)(u)]_{{\cal B}_{3}} +\] + +\end_inset + +y por la unicidad de la matriz de una aplicación lineal respecto a dos bases, + se tiene que +\begin_inset Formula $M_{{\cal B}_{3},{\cal B}_{1}}(g\circ f)=M_{{\cal B}_{3},{\cal B}_{2}}(g)M_{{\cal B}_{2},{\cal B}_{1}}(f)$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Sean +\begin_inset Formula $U$ +\end_inset + + y +\begin_inset Formula $V$ +\end_inset + + +\begin_inset Formula $K$ +\end_inset + +-espacios vectoriales con bases respectivas +\begin_inset Formula ${\cal B}$ +\end_inset + + y +\begin_inset Formula ${\cal B}'$ +\end_inset + +, +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + + una aplicación lineal y +\begin_inset Formula $A=M_{{\cal B}',{\cal B}}(f)$ +\end_inset + +. + Entonces +\begin_inset Formula $f$ +\end_inset + + es un isomorfismo si y sólo si +\begin_inset Formula $A$ +\end_inset + + es invertible, y entonces +\begin_inset Formula $A^{-1}=M_{{\cal B},{\cal B}'}(f^{-1})$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\implies]$ +\end_inset + + +\end_layout + +\end_inset + +Sea +\begin_inset Formula $B=M_{{\cal B},{\cal B}'}(f^{-1})$ +\end_inset + +: +\begin_inset Formula +\[ +AB=M_{{\cal B}',{\cal B}}(f)M_{{\cal B},{\cal B}'}(f^{-1})=M_{{\cal B}',{\cal B}'}(f\circ f^{-1})=M_{{\cal B}',{\cal B}'}(Id_{V})=I_{n} +\] + +\end_inset + + +\begin_inset Formula +\[ +BA=M_{{\cal B},{\cal B}'}(f^{-1})M_{{\cal B}',{\cal B}}(f)=M_{{\cal B},{\cal B}}(f^{-1}\circ f)=M_{{\cal B},{\cal B}}(Id_{U})=I_{n} +\] + +\end_inset + + +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\impliedby]$ +\end_inset + + +\end_layout + +\end_inset + +Al ser invertible es cuadrada, por lo que +\begin_inset Formula $\dim(U)=\dim(V)=n$ +\end_inset + +, y si consideramos +\begin_inset Formula $g:V\rightarrow U$ +\end_inset + + tal que +\begin_inset Formula $M_{{\cal B},{\cal B}'}(g)=A^{-1}$ +\end_inset + +, se tiene que +\begin_inset Formula +\[ +M_{{\cal B},{\cal B}}(g\circ f)=M_{{\cal B},{\cal B}'}(g)M_{{\cal B}',{\cal B}}(f)=A^{-1}A=I_{n}=M_{{\cal B},{\cal B}}(Id_{U})\implies g\circ f=Id_{U} +\] + +\end_inset + + +\begin_inset Formula +\[ +M_{{\cal B}',{\cal B}'}(f\circ g)=M_{{\cal B}',{\cal B}}(f)M_{{\cal B},{\cal B}'}(g)=AA^{-1}=I_{n}=M_{{\cal B}',{\cal B}'}(Id_{V})\implies f\circ g=Id_{V} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Así, si +\begin_inset Formula ${\cal B}$ +\end_inset + + y +\begin_inset Formula ${\cal B}'$ +\end_inset + + son bases de +\begin_inset Formula $V$ +\end_inset + +, como +\begin_inset Formula $M_{{\cal B},{\cal B}'}=M_{{\cal B},{\cal B}'}(Id_{V})$ +\end_inset + +, se tiene que +\begin_inset Formula +\[ +M_{{\cal B}',{\cal B}}^{-1}=(M_{{\cal B}',{\cal B}}(Id_{V}))^{-1}=M_{{\cal B},{\cal B}'}(Id_{V}^{-1})=M_{{\cal B},{\cal B}'}(Id_{V})=M_{{\cal B},{\cal B}'} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +También se tiene que si +\begin_inset Formula ${\cal B}_{1}$ +\end_inset + + y +\begin_inset Formula ${\cal B}_{2}$ +\end_inset + + son bases de +\begin_inset Formula $U$ +\end_inset + + y +\begin_inset Formula ${\cal B}'_{1}$ +\end_inset + + y +\begin_inset Formula ${\cal B}'_{2}$ +\end_inset + + son bases de +\begin_inset Formula $V$ +\end_inset + +, entonces +\begin_inset Formula +\[ +M_{{\cal B}'_{2},{\cal B}_{2}}(f)=M_{{\cal B}'_{2},{\cal B}_{2}}(Id_{V}\circ f\circ Id_{U})=M_{{\cal B}'_{2},{\cal B}'_{1}}\cdot M_{{\cal B}'_{1}{\cal B}_{1}}(f)\cdot M_{{\cal B}_{1},{\cal B}_{2}} +\] + +\end_inset + +Para +\begin_inset Formula $A,B\in M_{m,n}(K)$ +\end_inset + +, +\begin_inset Formula $A$ +\end_inset + + y +\begin_inset Formula $B$ +\end_inset + + son +\series bold +equivalentes +\series default + si existen matrices invertibles +\begin_inset Formula $P\in M_{m}(K)$ +\end_inset + + y +\begin_inset Formula $Q\in M_{n}(K)$ +\end_inset + + tales que +\begin_inset Formula $B=PAQ$ +\end_inset + +. + Esta es una relación de equivalencia. +\end_layout + +\begin_layout Standard +Se llama +\series bold +rango +\series default + de +\begin_inset Formula $A\in M_{m,n}(K)$ +\end_inset + + al máximo de columnas linealmente independientres consideradas como vectores + de +\begin_inset Formula $K^{m}$ +\end_inset + +, es decir, +\begin_inset Formula $\text{rang}(A)=\dim(<C_{1},\dots,C_{n}>)$ +\end_inset + +, y por tanto +\begin_inset Formula $\text{rang}(A)\leq m,n$ +\end_inset + +. + Dado que las columnas de +\begin_inset Formula $M_{{\cal B}',{\cal B}}(f)$ +\end_inset + + son las imágenes en +\begin_inset Formula $f$ +\end_inset + + de los elementos de +\begin_inset Formula ${\cal B}$ +\end_inset + + sobre +\begin_inset Formula ${\cal B}'$ +\end_inset + +, se tiene que +\begin_inset Formula $\text{rang}(M_{{\cal B}',{\cal B}}(f))=\text{rang}(f)$ +\end_inset + +, y como las matrices invertibles corresponden a isomorfismos, se tiene + que +\begin_inset Formula $A\in M_{n}(K)$ +\end_inset + + es invertible si y sólo si +\begin_inset Formula $\text{rang}(A)=n$ +\end_inset + +, para lo que basta con considerar el homomorfismo +\begin_inset Formula $f:K^{n}\rightarrow K^{n}$ +\end_inset + + con +\begin_inset Formula $M_{{\cal C},{\cal C}}(f)=A$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Dados +\begin_inset Formula $K$ +\end_inset + +-espacios vectoriales +\begin_inset Formula $U$ +\end_inset + + y +\begin_inset Formula $V$ +\end_inset + + con dimensiones respectivas +\begin_inset Formula $n$ +\end_inset + + y +\begin_inset Formula $m$ +\end_inset + +, y el homomorfismo +\begin_inset Formula $f:U\rightarrow V$ +\end_inset + +, existen bases +\begin_inset Formula ${\cal B}$ +\end_inset + + de +\begin_inset Formula $U$ +\end_inset + + y +\begin_inset Formula ${\cal B}'$ +\end_inset + + de +\begin_inset Formula $V$ +\end_inset + + tales que +\begin_inset Formula +\[ +M_{{\cal B}',{\cal B}}(f)=\left(\begin{array}{c|c} +I_{r} & 0\\ +\hline 0 & 0 +\end{array}\right)\in M_{m,n}(K) +\] + +\end_inset + +con +\begin_inset Formula $r=\text{rang}(f)$ +\end_inset + +. + +\series bold +Demostración: +\series default + Si +\begin_inset Formula $r=\text{rang}(f)$ +\end_inset + + entonces +\begin_inset Formula $\dim(\text{Nuc}(f))=n-r$ +\end_inset + +. + Además, si +\begin_inset Formula $\{u_{r+1},\dots,u_{n}\}$ +\end_inset + + es base de +\begin_inset Formula $\text{Nuc}(f)$ +\end_inset + + que se extiende a la base +\begin_inset Formula ${\cal B}=\{u_{1},\dots,u_{r},u_{r+1},\dots,u_{n}\}$ +\end_inset + + de +\begin_inset Formula $U$ +\end_inset + +, entonces +\begin_inset Formula $f(u_{r+1})=\dots=f(u_{n})=0$ +\end_inset + +, y +\begin_inset Formula $f(u_{1}),\dots,f(u_{r})$ +\end_inset + + son linealmente dependientes, dado que si +\begin_inset Formula $\alpha_{1}f(u_{1})+\dots+\alpha_{r}f(u_{r})=0$ +\end_inset + + entonces +\begin_inset Formula $\alpha_{1}u_{1}+\dots+\alpha_{r}u_{r}\in\text{Nuc}(f)=<u_{r+1},\dots,u_{n}>$ +\end_inset + + y como +\begin_inset Formula $<u_{1},\dots,u_{r}>\cap<u_{r+1},\dots,u_{n}>=\{0\}$ +\end_inset + +, entonces +\begin_inset Formula $\alpha_{1}u_{1}+\dots+\alpha_{r}u_{r}=0$ +\end_inset + + y por tanto +\begin_inset Formula $\alpha_{1}=\dots=\alpha_{r}=0$ +\end_inset + +. + Si extendemos este conjunto a la base +\begin_inset Formula ${\cal B}'=\{f(u_{1}),\dots,f(u_{r}),v_{r+1},\dots,v_{m}\}$ +\end_inset + +, se tiene la +\begin_inset Formula $M_{{\cal B}',{\cal B}}(f)$ +\end_inset + + buscada. +\end_layout + +\begin_layout Standard +Toda +\begin_inset Formula $A\in M_{m,n}(K)$ +\end_inset + + es equivalente a una de esta forma, con +\begin_inset Formula $r=\text{rang}(A)$ +\end_inset + +. + +\series bold +Demostración: +\series default + Sea +\begin_inset Formula $f:K^{n}\rightarrow K^{m}$ +\end_inset + + tal que +\begin_inset Formula $M_{{\cal C}',{\cal C}}(f)=A$ +\end_inset + +. + Entonces +\begin_inset Formula $M_{{\cal B}',{\cal B}}(f)=M_{{\cal B}',{\cal {\cal C}}'}\cdot A\cdot M_{{\cal C},{\cal B}}$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Llamamos +\series bold +matriz traspuesta +\series default + de +\begin_inset Formula $A=(a_{ij})\in M_{m,n}(K)$ +\end_inset + + a la matriz +\begin_inset Formula $A^{t}=(b_{ij})\in M_{n,m}(K)$ +\end_inset + + con +\begin_inset Formula $b_{ij}=a_{ji}$ +\end_inset + +. + Se verifica que +\begin_inset Formula $(A^{t})^{t}=A$ +\end_inset + +, +\begin_inset Formula $(\alpha A)^{t}=\alpha A^{t}$ +\end_inset + +, +\begin_inset Formula $(A+B)^{t}=A^{t}+B^{t}$ +\end_inset + +, +\begin_inset Formula $(AC)^{t}=C^{t}A^{t}$ +\end_inset + +, y si +\begin_inset Formula $A$ +\end_inset + + es invertible entonces +\begin_inset Formula $A^{t}$ +\end_inset + + también lo es y +\begin_inset Formula $(A^{t})^{-1}=(A^{-1})^{t}$ +\end_inset + +. + Así, si +\begin_inset Formula +\[ +B=\left(\begin{array}{c|c} +I_{r} & 0\\ +\hline 0 & 0 +\end{array}\right)\in M_{m,n}(K) +\] + +\end_inset + +con +\begin_inset Formula $r=\text{rang}(A)$ +\end_inset + + y +\begin_inset Formula $A=M_{m,n}(K)$ +\end_inset + +, existirán +\begin_inset Formula $P\in M_{m}(K)$ +\end_inset + + y +\begin_inset Formula $Q\in M_{n}(K)$ +\end_inset + + tales que +\begin_inset Formula $B=PAQ$ +\end_inset + +, por lo que +\begin_inset Formula $Q^{t}A^{t}P^{t}=(PAQ)^{t}=B^{t}$ +\end_inset + + con +\begin_inset Formula $\text{rang}(B^{t})=\text{rang}(B)$ +\end_inset + +, y por tanto +\begin_inset Formula $\text{rang}(A)=\text{rang}(A^{t})$ +\end_inset + +. +\end_layout + +\begin_layout Section +Matrices elementales. + Aplicaciones +\end_layout + +\begin_layout Standard +Llamamos +\series bold +matriz elemental +\series default + de tamaño +\begin_inset Formula $n$ +\end_inset + + a toda matriz obtenida al efectuar una operación elemental (por filas o + columnas) en +\begin_inset Formula $I_{n}$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Formula $E_{n}(i,j)$ +\end_inset + + es la resultante de intercambiar las filas +\begin_inset Formula $i$ +\end_inset + + y +\begin_inset Formula $j$ +\end_inset + +, o las columnas +\begin_inset Formula $i$ +\end_inset + + y +\begin_inset Formula $j$ +\end_inset + +, en +\begin_inset Formula $I_{n}$ +\end_inset + +. + +\begin_inset Formula $E_{n}(i,j)^{-1}=E_{n}(i,j)$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Formula $E_{n}(r[i])$ +\end_inset + + es la resultante de multiplicar por +\begin_inset Formula $r$ +\end_inset + + la fila +\begin_inset Formula $i$ +\end_inset + +, o la columna +\begin_inset Formula $i$ +\end_inset + +, en +\begin_inset Formula $I_{n}$ +\end_inset + +. + +\begin_inset Formula $E_{n}(r[i])^{-1}=E_{n}(r^{-1}[i])$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Formula $E_{n}([i]+r[j])$ +\end_inset + + es la resultante de añadir a la fila +\begin_inset Formula $i$ +\end_inset + + la fila +\begin_inset Formula $j$ +\end_inset + + multiplicada por +\begin_inset Formula $r$ +\end_inset + +, o a la columna +\begin_inset Formula $j$ +\end_inset + + la columna +\begin_inset Formula $i$ +\end_inset + + multiplicada por +\begin_inset Formula $r$ +\end_inset + +, en +\begin_inset Formula $I_{n}$ +\end_inset + +. + +\begin_inset Formula $E_{n}([i]+r[j])^{-1}=E_{n}([i]-r[j])$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $B$ +\end_inset + + se obtiene al realizar una operación elemental por filas en +\begin_inset Formula $A$ +\end_inset + + y +\begin_inset Formula $E$ +\end_inset + + al realizar la misma en +\begin_inset Formula $I_{m}$ +\end_inset + +, entonces +\begin_inset Formula $B=EA$ +\end_inset + +. + Del mismo modo, si +\begin_inset Formula $B$ +\end_inset + + se obtiene de aplicar una operación elemental por columnas en +\begin_inset Formula $A$ +\end_inset + + y +\begin_inset Formula $E$ +\end_inset + + al aplicarla a +\begin_inset Formula $I_{n}$ +\end_inset + +, entonces +\begin_inset Formula $B=AE$ +\end_inset + +. + Así, realizar una serie de estas operaciones en una matriz equivale a multiplic +arla por uno o ambos lados por un producto de matrices elementales, el cual + es invertible. + Dada una matriz +\begin_inset Formula $A$ +\end_inset + +, para obtener las matrices +\begin_inset Formula $P$ +\end_inset + + y +\begin_inset Formula $Q$ +\end_inset + + tales que +\begin_inset Formula +\[ +PAQ=\left(\begin{array}{c|c} +I_{r} & 0\\ +\hline 0 & 0 +\end{array}\right) +\] + +\end_inset + +podemos partir de +\begin_inset Formula +\[ +\left(\begin{array}{c|c} +A & I_{m}\\ +\hline I_{n} +\end{array}\right) +\] + +\end_inset + +y realizar operaciones elementales hasta llegar a una matriz de la forma +\begin_inset Formula +\[ +\left(\begin{array}{c|c} +\begin{array}{c|c} +I_{r} & 0\\ +\hline 0 & 0 +\end{array} & P\\ +\hline Q +\end{array}\right) +\] + +\end_inset + + +\begin_inset Formula $A\in M_{n}(K)$ +\end_inset + + es invertible cuando tiene rango precisamente +\begin_inset Formula $n$ +\end_inset + +, por lo que al hacer operaciones elementales por filas para obtener una + matriz escalonada reducida, esta será precisamente +\begin_inset Formula $I_{n}$ +\end_inset + +, de forma que +\begin_inset Formula $(E_{k}\cdots E_{1})A=I_{n}$ +\end_inset + + y por tanto +\begin_inset Formula $A^{-1}=E_{k}\cdots E_{1}$ +\end_inset + +, de forma que +\begin_inset Formula $A^{-1}$ +\end_inset + + es la matriz resultante de efectuar en +\begin_inset Formula $I_{n}$ +\end_inset + + las mismas operaciones elementales fila que se hacen en +\begin_inset Formula $A$ +\end_inset + +. + A efectos prácticos, formamos la matriz +\begin_inset Formula $\left(\begin{array}{c|c} +A & I_{n}\end{array}\right)$ +\end_inset + + y hacemos operaciones elementales por filas hasta llegar a +\begin_inset Formula $\left(\begin{array}{c|c} +I_{n} & A^{-1}\end{array}\right)$ +\end_inset + +. + Por otro lado, si +\begin_inset Formula $A^{-1}=E_{k}\cdots E_{1}$ +\end_inset + +, entonces +\begin_inset Formula $A=(A^{-1})^{-1}=(E_{k}\cdots E_{1})^{-1}=E_{1}^{-1}\cdots E_{k}^{-1}$ +\end_inset + +, de forma que toda matriz invertible es producto de matrices elementales. +\end_layout + +\end_body +\end_document diff --git a/algl/n3.lyx b/algl/n3.lyx new file mode 100644 index 0000000..99baa10 --- /dev/null +++ b/algl/n3.lyx @@ -0,0 +1,652 @@ +#LyX 2.3 created this file. For more info see http://www.lyx.org/ +\lyxformat 544 +\begin_document +\begin_header +\save_transient_properties true +\origin unavailable +\textclass book +\use_default_options true +\maintain_unincluded_children false +\language spanish +\language_package default +\inputencoding auto +\fontencoding global +\font_roman "default" "default" +\font_sans "default" "default" +\font_typewriter "default" "default" +\font_math "auto" "auto" +\font_default_family default +\use_non_tex_fonts false +\font_sc false +\font_osf false +\font_sf_scale 100 100 +\font_tt_scale 100 100 +\use_microtype false +\use_dash_ligatures true +\graphics default +\default_output_format default +\output_sync 0 +\bibtex_command default +\index_command default +\paperfontsize default +\spacing single +\use_hyperref false +\papersize default +\use_geometry false +\use_package amsmath 1 +\use_package amssymb 1 +\use_package cancel 1 +\use_package esint 1 +\use_package mathdots 1 +\use_package mathtools 1 +\use_package mhchem 1 +\use_package stackrel 1 +\use_package stmaryrd 1 +\use_package undertilde 1 +\cite_engine basic +\cite_engine_type default +\biblio_style plain +\use_bibtopic false +\use_indices false +\paperorientation portrait +\suppress_date false +\justification true +\use_refstyle 1 +\use_minted 0 +\index Index +\shortcut idx +\color #008000 +\end_index +\secnumdepth 3 +\tocdepth 3 +\paragraph_separation indent +\paragraph_indentation default +\is_math_indent 0 +\math_numbering_side default +\quotes_style swiss +\dynamic_quotes 0 +\papercolumns 1 +\papersides 1 +\paperpagestyle default +\tracking_changes false +\output_changes false +\html_math_output 0 +\html_css_as_file 0 +\html_be_strict false +\end_header + +\begin_body + +\begin_layout Standard +Una +\series bold +ecuación lineal +\series default + en las +\begin_inset Formula $n$ +\end_inset + + +\series bold +incógnitas +\series default + +\begin_inset Formula $x_{1},\dots,x_{n}$ +\end_inset + + sobre el cuerpo +\begin_inset Formula $K$ +\end_inset + + es una expresión de la forma +\begin_inset Formula $a_{1}x_{1}+\dots+a_{n}x_{n}=b$ +\end_inset + +, con los +\begin_inset Formula $a_{i}\in K$ +\end_inset + + ( +\series bold +coeficientes +\series default +) y +\begin_inset Formula $b\in K$ +\end_inset + + ( +\series bold +término independiente +\series default +). + Un +\series bold +sistema de +\begin_inset Formula $m$ +\end_inset + + ecuaciones lineales +\series default + con +\begin_inset Formula $n$ +\end_inset + + incógnitas sobre el cuerpo +\series bold + +\begin_inset Formula $K$ +\end_inset + + +\series default + tiene la forma +\begin_inset Formula +\[ +\left.\begin{array}{ccccccc} +a_{11}x_{1} & + & \dots & + & a_{1n}x_{n} & = & b_{1}\\ + & & & & & \vdots\\ +a_{m1}x_{1} & + & \dots & + & a_{mn}x_{n} & = & b_{m} +\end{array}\right\} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Puede expresarse matricialmente de la forma +\begin_inset Formula $AX=B$ +\end_inset + +, donde +\begin_inset Formula $A=(a_{ij})\in M_{m,n}(K)$ +\end_inset + + es la +\series bold +matriz de los coeficientes +\series default +, +\begin_inset Formula $B=(b_{i})\in M_{m,1}(K)$ +\end_inset + + es la +\series bold +matriz de los términos independientes +\series default + y +\begin_inset Formula $X=(x_{i})\in M_{n,1}(K)$ +\end_inset + + es la matriz de incógnitas. + A la matriz +\begin_inset Formula $(A|B)\in M_{m,n+1}(K)$ +\end_inset + + se le llama +\series bold +matriz ampliada +\series default + del sistema. + Un sistema es +\series bold +homogéneo +\series default + si +\begin_inset Formula $B=0$ +\end_inset + +, y a cada sistema +\begin_inset Formula $AX=B$ +\end_inset + + se le puede asociar el sistema homogéneo +\begin_inset Formula $AX=0$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Se llama +\series bold +solución +\series default + a toda +\begin_inset Formula $n$ +\end_inset + +-upla +\begin_inset Formula $(r_{1},\dots,r_{n})\in K^{n}$ +\end_inset + + tal que si +\begin_inset Formula $R=(r_{i})\in M_{n,1}(K)$ +\end_inset + + entonces +\begin_inset Formula $AR=B$ +\end_inset + +. + Un sistema es +\series bold +compatible +\series default + si tiene alguna solución, +\series bold +determinado +\series default + si tiene solo una e +\series bold +indeterminado +\series default + si tiene más; o +\series bold +incompatible +\series default + si no tiene ninguna. + +\series bold +Discutir +\series default + un sistema es determinar su compatibilidad, y +\series bold +resolverlo +\series default + es encontrar las soluciones. +\end_layout + +\begin_layout Standard + +\series bold +Teorema: +\series default + Si un sistema +\begin_inset Formula $AX=B$ +\end_inset + + tiene una solución +\begin_inset Formula $P$ +\end_inset + +, todas las soluciones son de la forma +\begin_inset Formula $P+M$ +\end_inset + +, donde +\begin_inset Formula $M$ +\end_inset + + es solución de +\begin_inset Formula $AX=0$ +\end_inset + +. +\end_layout + +\begin_layout Section +Teorema de Rouché-Frobenius +\end_layout + +\begin_layout Standard +Un sistema +\begin_inset Formula $AX=B$ +\end_inset + + es compatible si y sólo si +\begin_inset Formula $\text{rang}(A)=\text{rang}(A|B)$ +\end_inset + +, en cuyo caso es determinado si +\begin_inset Formula $\text{rang}(A)=n$ +\end_inset + +. + En concreto, si +\begin_inset Formula $k=n-\text{rang}(A)>0$ +\end_inset + +, existen +\begin_inset Formula $u_{1},\dots,u_{k}$ +\end_inset + + soluciones linealmente independientes de +\begin_inset Formula $AX=0$ +\end_inset + + tales que cualquier solución del sistema es de la forma +\begin_inset Formula $x_{0}+\lambda_{1}u_{1}+\dots+\lambda_{k}u_{k}$ +\end_inset + +. + Decimos del sistema que +\series bold +depende de +\begin_inset Formula $k$ +\end_inset + + parámetros +\series default + +\begin_inset Formula $\lambda_{1},\dots,\lambda_{k}$ +\end_inset + + o que tiene +\begin_inset Formula $k$ +\end_inset + + +\series bold +grados de libertad +\series default +. +\end_layout + +\begin_layout Standard + +\series bold +Demostración: +\series default + Si tenemos la aplicación +\begin_inset Formula $f_{A}:K^{n}\rightarrow K^{m}$ +\end_inset + + tal que +\begin_inset Formula $A=M_{{\cal C^{0}},{\cal C}}(f)$ +\end_inset + +, entonces si +\begin_inset Formula $K^{n}=<u_{1},\dots,u_{n}>$ +\end_inset + + y +\begin_inset Formula $v$ +\end_inset + + es el vector definido por +\begin_inset Formula $B$ +\end_inset + +, el conjunto de soluciones es +\begin_inset Formula $f^{-1}(v)=\{x\in K^{n}|f(x)=v\}$ +\end_inset + +. + Entonces, +\begin_inset Formula +\begin{multline*} +\exists x\in U:f(x)=v\iff v\in\text{Im}(f)\iff<f(u_{1}),\dots,f(u_{n}),v>=<f(u_{1}),\dots,f(u_{n})>\iff\\ +\iff\dim(<f(u_{1}),\dots,f(u_{n}),v>)=\dim(<f(u_{1}),\dots,f(u_{n})>)=\dim(\text{Im}(f))=\text{rang}(f) +\end{multline*} + +\end_inset + +Por tanto +\begin_inset Formula $AX=B$ +\end_inset + + es compatible si y sólo si +\begin_inset Formula $\text{rang}(A)=\text{rang}(A|B)$ +\end_inset + +. + Por otro lado, si +\begin_inset Formula $f(x_{0})=v$ +\end_inset + +, las soluciones serán +\begin_inset Formula $f^{-1}(v)=\{u\in U|f(u)=v\}=x_{0}+\text{Nuc}(f)$ +\end_inset + +. + Como además +\begin_inset Formula $\dim(K^{n})=\text{rang}(f)+\dim(\text{Nuc}(f))$ +\end_inset + +, entonces +\begin_inset Formula $k:=\dim(\text{Nuc}(f))=n-\text{rang}(f)$ +\end_inset + +, por lo que existen +\begin_inset Formula $k$ +\end_inset + + soluciones linealmente independientes de +\begin_inset Formula $AX=0$ +\end_inset + + (una base de +\begin_inset Formula $\text{Nuc}(f)$ +\end_inset + +). + Por tanto las soluciones del sistema homogéneo serán combinaciones lineales + de dicha base. +\end_layout + +\begin_layout Section +Resolución de sistemas de ecuaciones lineales. + Método de Gauss +\end_layout + +\begin_layout Standard +Dos sistemas de +\begin_inset Formula $m$ +\end_inset + + ecuaciones lineales con +\begin_inset Formula $n$ +\end_inset + + incógnitas sobre un mismo cuerpo son +\series bold +e +\begin_inset ERT +status open + +\begin_layout Plain Layout + +\series bold + +\backslash +- +\end_layout + +\end_inset + +qui +\begin_inset ERT +status open + +\begin_layout Plain Layout + +\series bold + +\backslash +- +\end_layout + +\end_inset + +va +\begin_inset ERT +status open + +\begin_layout Plain Layout + +\series bold + +\backslash +- +\end_layout + +\end_inset + +len +\begin_inset ERT +status open + +\begin_layout Plain Layout + +\series bold + +\backslash +- +\end_layout + +\end_inset + +tes +\series default + si tienen las mismas soluciones. + Si +\begin_inset Formula $P\in M_{m}(K)$ +\end_inset + +, +\begin_inset Formula $(PA)X=PB$ +\end_inset + + es equivalente a +\begin_inset Formula $AX=B$ +\end_inset + +, y en particular, si +\begin_inset Formula $E\in M_{m}(K)$ +\end_inset + + es una matriz elemental, +\begin_inset Formula $(EA)X=EB$ +\end_inset + + también lo es, por lo que al hacer operaciones elementales por filas sobre + +\begin_inset Formula $(A|B)$ +\end_inset + + se obtiene un sistema con las mismas soluciones. +\end_layout + +\begin_layout Standard +El +\series bold +método de Gauss +\series default + comienza por convertir la matriz ampliada a una escalonada reducida por + filas +\begin_inset Formula $(A'|B')$ +\end_inset + +. + Si obtenemos que +\begin_inset Formula $\text{rang}(A|B)>\text{rang}(A)$ +\end_inset + +, el sistema es incompatible. + Si +\begin_inset Formula $r=\text{rang}(A)=\text{rang}(A|B)$ +\end_inset + +, las filas nulas de +\begin_inset Formula $A'$ +\end_inset + + lo son de +\begin_inset Formula $B'$ +\end_inset + +. + Reordenamos las incógnitas, lo que equivale a reordenar las columnas de + +\begin_inset Formula $A'$ +\end_inset + +, para conseguir un sistema de la forma +\begin_inset Formula +\[ +\left(\begin{array}{c|c} +I_{r} & C\\ +\hline 0 & 0 +\end{array}\right)\left(\begin{array}{c} +y_{1}\\ +\vdots\\ +y_{r}\\ +\hline y_{r+1}\\ +\vdots\\ +y_{n} +\end{array}\right)=\left(\begin{array}{c} +b_{1}^{\prime}\\ +\vdots\\ +b_{r}^{\prime}\\ +\hline 0\\ +\vdots\\ +0 +\end{array}\right) +\] + +\end_inset + +Donde +\begin_inset Formula $y_{1},\dots,y_{n}$ +\end_inset + + son los +\begin_inset Formula $x_{1},\dots,x_{n}$ +\end_inset + + reordenados de la misma forma que las columnas. + Esto equivale a +\begin_inset Formula +\[ +I_{r}\left(\begin{array}{c} +y_{1}\\ +\vdots\\ +y_{r} +\end{array}\right)+C\left(\begin{array}{c} +y_{r+1}\\ +\vdots\\ +y_{n} +\end{array}\right)=\left(\begin{array}{c} +b_{1}^{\prime}\\ +\vdots\\ +b_{r}^{\prime} +\end{array}\right)\implies\left(\begin{array}{c} +y_{1}\\ +\vdots\\ +y_{r} +\end{array}\right)=\left(\begin{array}{c} +b_{1}^{\prime}\\ +\vdots\\ +b_{r}^{\prime} +\end{array}\right)-C\left(\begin{array}{c} +y_{r+1}\\ +\vdots\\ +y_{n} +\end{array}\right) +\] + +\end_inset + +De modo que al asignar valores arbitrarios a +\begin_inset Formula $y_{r+1},\dots,y_{n}$ +\end_inset + +, que llamamos +\series bold +incógnitas libres +\series default +, obtenemos valores de +\begin_inset Formula $y_{1},\dots,y_{r}$ +\end_inset + +, que llamamos +\series bold +incógnitas principales +\series default +. +\end_layout + +\end_body +\end_document diff --git a/algl/n4.lyx b/algl/n4.lyx new file mode 100644 index 0000000..cf26416 --- /dev/null +++ b/algl/n4.lyx @@ -0,0 +1,1759 @@ +#LyX 2.3 created this file. For more info see http://www.lyx.org/ +\lyxformat 544 +\begin_document +\begin_header +\save_transient_properties true +\origin unavailable +\textclass book +\use_default_options true +\maintain_unincluded_children false +\language spanish +\language_package default +\inputencoding auto +\fontencoding global +\font_roman "default" "default" +\font_sans "default" "default" +\font_typewriter "default" "default" +\font_math "auto" "auto" +\font_default_family default +\use_non_tex_fonts false +\font_sc false +\font_osf false +\font_sf_scale 100 100 +\font_tt_scale 100 100 +\use_microtype false +\use_dash_ligatures true +\graphics default +\default_output_format default +\output_sync 0 +\bibtex_command default +\index_command default +\paperfontsize default +\spacing single +\use_hyperref false +\papersize default +\use_geometry false +\use_package amsmath 1 +\use_package amssymb 1 +\use_package cancel 1 +\use_package esint 1 +\use_package mathdots 1 +\use_package mathtools 1 +\use_package mhchem 1 +\use_package stackrel 1 +\use_package stmaryrd 1 +\use_package undertilde 1 +\cite_engine basic +\cite_engine_type default +\biblio_style plain +\use_bibtopic false +\use_indices false +\paperorientation portrait +\suppress_date false +\justification true +\use_refstyle 1 +\use_minted 0 +\index Index +\shortcut idx +\color #008000 +\end_index +\secnumdepth 3 +\tocdepth 3 +\paragraph_separation indent +\paragraph_indentation default +\is_math_indent 0 +\math_numbering_side default +\quotes_style swiss +\dynamic_quotes 0 +\papercolumns 1 +\papersides 1 +\paperpagestyle default +\tracking_changes false +\output_changes false +\html_math_output 0 +\html_css_as_file 0 +\html_be_strict false +\end_header + +\begin_body + +\begin_layout Section +Determinante de una matriz. + Propiedades +\end_layout + +\begin_layout Standard +Una aplicación +\begin_inset Formula $f:U_{1}\times\dots\times U_{n}\rightarrow V$ +\end_inset + + es una +\series bold +aplicación multilineal +\series default + si es lineal en cada una de las +\begin_inset Formula $n$ +\end_inset + + variables, es decir, si +\begin_inset Formula +\[ +f(u_{1},\dots,\alpha u_{i}+\beta u_{i}^{\prime},\dots,u_{n})=\alpha f(u_{1},\dots,u_{i},\dots,u_{n})+\beta f(u_{1},\dots,u_{i}^{\prime},\dots,u_{n}) +\] + +\end_inset + +Una aplicación multilineal +\begin_inset Formula $f:U^{n}\rightarrow V$ +\end_inset + + se llama +\series bold +aplicación +\begin_inset Formula $n$ +\end_inset + +-lineal +\series default +. + Si además +\begin_inset Formula $V=K$ +\end_inset + + es una +\series bold +forma +\begin_inset Formula $n$ +\end_inset + +-lineal +\series default +. + Una forma +\begin_inset Formula $n$ +\end_inset + +-lineal +\begin_inset Formula $f:U^{n}\rightarrow K$ +\end_inset + + es +\series bold +alternada +\series default + si se anula en cada +\begin_inset Formula $n$ +\end_inset + +-upla con dos componentes iguales, es decir, tal que +\begin_inset Formula $f(u_{1},\dots,u_{k},\dots,u_{l},\dots,u_{n})=0$ +\end_inset + + cuando +\begin_inset Formula $u_{k}=u_{l}$ +\end_inset + + (con +\begin_inset Formula $k\neq l$ +\end_inset + +). +\end_layout + +\begin_layout Standard +Una +\series bold +aplicación determinante +\series default + +\begin_inset Formula $\det:M_{n}(K)\rightarrow K$ +\end_inset + + es una forma +\begin_inset Formula $n$ +\end_inset + +-lineal alternada que a cada matriz cuadrada +\begin_inset Formula $A$ +\end_inset + + le asigna un escalar, llamado +\series bold +determinante +\series default + de +\begin_inset Formula $A$ +\end_inset + +, que denotamos +\begin_inset Formula $\det(A)$ +\end_inset + +, +\begin_inset Formula $|A|$ +\end_inset + + o +\begin_inset Formula $\det(A_{1},\dots,A_{n})$ +\end_inset + + (donde +\begin_inset Formula $A_{i}$ +\end_inset + + son las columnas de +\begin_inset Formula $A$ +\end_inset + +), tal que +\begin_inset Formula $|I_{n}|=1$ +\end_inset + +. + Algunas aplicaciones determinantes son: +\end_layout + +\begin_layout Enumerate +La aplicación +\begin_inset Formula $||:M_{2}(K)\rightarrow K$ +\end_inset + + dada por +\begin_inset Formula +\[ +\left|\begin{array}{cc} +a_{11} & a_{12}\\ +a_{21} & a_{22} +\end{array}\right|=a_{11}a_{22}-a_{12}a_{21} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +La +\series bold +regla de Sarrus +\series default +, aplicación +\begin_inset Formula $||:M_{3}(K)\rightarrow K$ +\end_inset + + dada por +\begin_inset Formula +\[ +\left|\begin{array}{ccc} +a_{11} & a_{12} & a_{13}\\ +a_{21} & a_{22} & a_{23}\\ +a_{31} & a_{32} & a_{33} +\end{array}\right|=a_{11}a_{22}a_{33}+a_{12}a_{23}a_{31}+a_{13}a_{21}a_{32}-a_{11}a_{23}a_{32}-a_{13}a_{22}a_{31}-a_{12}a_{21}a_{33} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Las aplicaciones determinantes verifican que: +\end_layout + +\begin_layout Enumerate +\begin_inset Formula +\[ +\left|\begin{array}{cccc} +a_{1} & 0 & \cdots & 0\\ +0 & a_{2} & \cdots & 0\\ +\vdots & \vdots & \ddots & \vdots\\ +0 & 0 & \cdots & a_{n} +\end{array}\right|=a_{1}a_{2}\cdots a_{n} +\] + +\end_inset + +Si +\begin_inset Formula $\{e_{1},\dots,e_{n}\}$ +\end_inset + + es la base canónica de +\begin_inset Formula $K^{n}$ +\end_inset + +, +\begin_inset Formula +\[ +\left|\begin{array}{cccc} +a_{1} & 0 & \cdots & 0\\ +0 & a_{2} & \cdots & 0\\ +\vdots & \vdots & \ddots & \vdots\\ +0 & 0 & \cdots & a_{n} +\end{array}\right|=\det(a_{1}e_{1},\dots,a_{n}e_{n})=a_{1}\cdots a_{n}\det(e_{1},\dots,e_{n})=a_{1}\cdots a_{n} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $A$ +\end_inset + + tiene una columna nula entonces +\begin_inset Formula $\det(A)=0$ +\end_inset + +. +\begin_inset Newline newline +\end_inset + +Si +\begin_inset Formula $A_{i}=0$ +\end_inset + +, entonces +\begin_inset Formula +\[ +\begin{array}{c} +\det(A_{1},\dots,A_{i-1},0,A_{i+1},\dots,A_{n})=\det(A_{1},\dots,A_{i-1},0+0,A_{i+1},\dots,A_{n})=\\ +=\det(A_{1},\dots,A_{i-1},0,A_{i+1},\dots,A_{n})+\det(A_{1},\dots,A_{i-1},0,A_{i+1},\dots,A_{n}) +\end{array} +\] + +\end_inset + +luego +\begin_inset Formula $\det A=0$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Al intercambiar dos columnas, el determinante cambia de signo. +\begin_inset Formula +\[ +\begin{array}{c} +0=\det(A_{1},\dots,A_{i}+A_{j},\dots,A_{i}+A_{j},\dots,A_{n})=\\ +=\det(A_{1},\dots,A_{i},\dots,A_{i},\dots,A_{n})+\det(A_{1},\dots,A_{i},\dots,A_{j},\dots,A_{n})+\\ ++\det(A_{1},\dots,A_{j},\dots,A_{i},\dots,A_{n})+\det(A_{1},\dots,A_{j},\dots,A_{j},\dots,A_{n})=\\ +=\det(A_{1},\dots,A_{i},\dots,A_{j},\dots,A_{n})+\det(A_{1},\dots,A_{j},\dots,A_{i},\dots,A_{n}) +\end{array} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +Si a una columna se le añade otra multiplicada por un escalar, el determinante + no varía. +\begin_inset Newline newline +\end_inset + + +\begin_inset Formula +\[ +\begin{array}{c} +\det(A_{1},\dots,A_{i}+\alpha A_{j},\dots,A_{j},\dots,A_{n})=\\ +=\det(A_{1},\dots,A_{i},\dots,A_{j},\dots,A_{n})+\alpha\det(A_{1},\dots,A_{j},\dots,A_{j},\dots,A_{n})=\\ +=\det(A_{1},\dots,A_{i},\dots,A_{j},\dots,A_{n}) +\end{array} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +Si las columnas de una matriz cuadrada son linealmente dependientes, su + determinante es 0. + Por tanto una matriz no invertible tiene determinante 0. +\begin_inset Newline newline +\end_inset + +Habrá una columna que será combinación lineal del resto: +\begin_inset Formula $A_{k}=\sum_{j\neq k}\alpha_{j}A_{j}$ +\end_inset + +. + Así, +\begin_inset Formula +\[ +\begin{array}{c} +\det(A_{1},\dots,A_{k},\dots,A_{n})=\det(A_{1},\dots,\sum_{j\neq k}\alpha_{j}A_{j},\dots,A_{n})=\\ +=\sum_{j\neq k}\alpha_{j}\det(A_{1},\dots,A_{j},\dots,A_{n})=0 +\end{array} +\] + +\end_inset + +Ya que cada matriz del último sumatorio tiene dos columnas iguales. +\end_layout + +\begin_layout Standard +De aquí podemos deducir que +\begin_inset Formula $|E_{n}(i,j)|=-1$ +\end_inset + +, +\begin_inset Formula $|E_{n}(\alpha[i])|=\alpha$ +\end_inset + + y +\begin_inset Formula $|E_{n}([i]+\alpha[j])|=1$ +\end_inset + +, y que si +\begin_inset Formula $A,E\in M_{n}(K)$ +\end_inset + +, siendo +\begin_inset Formula $E$ +\end_inset + + una matriz elemental, entonces +\begin_inset Formula $|AE|=|A||E|$ +\end_inset + +. + Se deducen los siguientes teoremas: +\end_layout + +\begin_layout Enumerate +Una matriz cuadrada +\begin_inset Formula $A$ +\end_inset + + es invertible si y sólo si +\begin_inset Formula $|A|\neq0$ +\end_inset + +. +\end_layout + +\begin_deeper +\begin_layout Enumerate +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\implies]$ +\end_inset + + +\end_layout + +\end_inset + +Toda matriz invertible es producto de matrices elementales, y por lo anterior, + +\begin_inset Formula $|A|=|I_{n}E_{1}\cdots E_{k}|=|I_{n}||E_{1}|\cdots|E_{k}|=|E_{1}|\cdots|E_{k}|$ +\end_inset + +. + Como ninguno de los factores es nulo, se tiene que +\begin_inset Formula $|A|\neq0$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\impliedby]$ +\end_inset + + +\end_layout + +\end_inset + +Inmediato de la última propiedad. +\end_layout + +\end_deeper +\begin_layout Enumerate +Si +\begin_inset Formula $A,B\in M_{n}(K)$ +\end_inset + +, entonces +\begin_inset Formula $|AB|=|A||B|$ +\end_inset + +. +\begin_inset Newline newline +\end_inset + +Si alguna de las dos no es invertible, su producto tampoco (pues si lo fuera, + +\begin_inset Formula $A$ +\end_inset + + y +\begin_inset Formula $B$ +\end_inset + + serían invertibles). + En tal caso, +\begin_inset Formula $|AB|=0=|A||B|$ +\end_inset + +. + Si son ambas invertibles, existen matrices elementales +\begin_inset Formula $E_{1},\dots,E_{k}$ +\end_inset + + con +\begin_inset Formula $B=E_{1}\cdots E_{k}$ +\end_inset + +, por lo que +\begin_inset Formula $|AB|=|AE_{1}\cdots E_{k}|=|A||E_{1}|\cdots|E_{k}|=|A||B|$ +\end_inset + +. +\end_layout + +\begin_layout Standard +De aquí tenemos que +\begin_inset Formula $|A^{-1}|=|A|^{-1}$ +\end_inset + +, pues +\begin_inset Formula $1=|I_{n}|=|AA^{-1}|=|A||A^{-1}|$ +\end_inset + +. + Tenemos también que la aplicación determinante es única, pues +\begin_inset Formula $\det(A)=0$ +\end_inset + + para matrices no invertibles y +\begin_inset Formula $\det(A)=|E_{1}|\cdots|E_{k}|$ +\end_inset + + para aquellas que sí lo son, y podemos entonces comprobar que esta operación + está bien definida. +\end_layout + +\begin_layout Standard + +\series bold +Teorema: +\series default + +\begin_inset Formula $|A^{t}|=|A|$ +\end_inset + +. + +\series bold +Demostración: +\series default + Si +\begin_inset Formula $A$ +\end_inset + + no es invertible, +\begin_inset Formula $A^{t}$ +\end_inset + + tampoco, por lo que +\begin_inset Formula $|A^{t}|=0=|A|$ +\end_inset + +. + Si lo es, existen +\begin_inset Formula $E_{1},\dots,E_{k}$ +\end_inset + + con +\begin_inset Formula $A=E_{1}\cdots E_{k}$ +\end_inset + +, por lo que +\begin_inset Formula $|A^{t}|=|(E_{1}\cdots E_{k})^{t}|=|E_{k}^{t}\cdots E_{1}^{t}|=|E_{k}^{t}|\cdots|E_{1}^{t}|=|E_{1}|\cdots|E_{k}|=|E_{1}\cdots E_{k}|=|A|$ +\end_inset + +. + Esto significa que todo lo relativo a determinantes que se diga para columnas + también es válido para filas. +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $A=(a_{ij})\in M_{n}(K)$ +\end_inset + + e +\begin_inset Formula $i,j\in\{1,\dots,n\}$ +\end_inset + +, llamamos +\series bold +menor complementario +\series default + del elemento +\begin_inset Formula $a_{ij}$ +\end_inset + + al determinante +\begin_inset Formula $|A_{ij}|$ +\end_inset + + de la matriz +\begin_inset Formula $A_{ij}\in M_{n-1}(K)$ +\end_inset + + resultado de eliminar la fila +\begin_inset Formula $i$ +\end_inset + + y la columna +\begin_inset Formula $j$ +\end_inset + + de +\begin_inset Formula $A$ +\end_inset + +. + Llamamos +\series bold +adjunto +\series default + de +\begin_inset Formula $a_{ij}$ +\end_inset + + en +\begin_inset Formula $A$ +\end_inset + + al escalar +\begin_inset Formula $\Delta_{ij}:=(-1)^{i+j}|A_{ij}|$ +\end_inset + +. +\end_layout + +\begin_layout Standard + +\series bold +Teorema: +\series default + Las aplicaciones +\begin_inset Formula $||:M_{n}(K)\rightarrow K$ +\end_inset + + definidas para +\begin_inset Formula $n=1$ +\end_inset + + como +\begin_inset Formula $|(a)|=a$ +\end_inset + + y para +\begin_inset Formula $n>1$ +\end_inset + + como +\begin_inset Formula $|(a_{ij})|=a_{11}\Delta_{11}+\dots+a_{1n}\Delta_{1n}$ +\end_inset + + son aplicaciones determinante. + +\series bold +Demostración: +\series default + Para +\begin_inset Formula $n=1$ +\end_inset + + es trivial. + Ahora supongamos que la aplicación determinante está definida para +\begin_inset Formula $n-1$ +\end_inset + + y probamos que se cumplen las condiciones para +\begin_inset Formula $n-1$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Multilineal: Sea +\begin_inset Formula $A=(a_{ij})=(A_{1},\dots,A_{n})\in M_{n}(K)$ +\end_inset + + y +\begin_inset Formula $A^{\prime}=(a_{ij}^{\prime})=(A_{1},\dots,\alpha A_{k},\dots,A_{n})$ +\end_inset + +. + Entonces +\begin_inset Formula $a_{ik}^{\prime}=\alpha a_{ik}$ +\end_inset + + y para +\begin_inset Formula $j\neq k$ +\end_inset + +, +\begin_inset Formula $a_{ij}^{\prime}=a_{ij}$ +\end_inset + +. + Si llamamos +\begin_inset Formula $\Delta_{ij}$ +\end_inset + + y +\begin_inset Formula $\Delta_{ij}^{\prime}$ +\end_inset + + a los correspondientes adjuntos, +\begin_inset Formula $\Delta_{ik}^{\prime}=\Delta_{ik}$ +\end_inset + + y para +\begin_inset Formula $j\neq k$ +\end_inset + +, +\begin_inset Formula $\Delta_{ij}^{\prime}=\alpha\Delta_{ij}$ +\end_inset + +. + Así, +\begin_inset Formula +\[ +\begin{array}{c} +|A^{\prime}|=a_{11}^{\prime}\Delta_{11}^{\prime}+\dots+a_{1n}^{\prime}\Delta_{1n}^{\prime}=\\ +=a_{11}\alpha\Delta_{11}+\dots+a_{1(k-1)}\alpha\Delta_{1(k-1)}+\alpha a_{1k}\Delta_{ik}+a_{1(k+1)}\alpha\Delta_{i(k+1)}+\dots+a_{1n}\alpha\Delta_{in}=\\ +=\alpha(a_{11}\Delta_{11}+\dots+a_{1n}\Delta_{1n})=\alpha|A| +\end{array} +\] + +\end_inset + +Del mismo modo, sea +\begin_inset Formula $A=(a_{ij})=(A_{1},\dots,A_{k}^{\prime}+A_{k}^{\prime\prime},\dots,A_{n})$ +\end_inset + + y sean +\begin_inset Formula $A^{\prime}=(a_{ij}^{\prime})=(A_{1},\dots,A_{k}^{\prime},\dots,A_{n})$ +\end_inset + + y +\begin_inset Formula $A^{\prime\prime}=(a_{ij}^{\prime\prime})=(A_{1},\dots,A_{k}^{\prime\prime},\dots,A_{n})$ +\end_inset + +. + Entonces +\begin_inset Formula $a_{ik}=a_{ik}^{\prime}+a_{ik}^{\prime\prime}$ +\end_inset + + y si +\begin_inset Formula $j\neq k$ +\end_inset + +, +\begin_inset Formula $a_{ij}=a_{ij}^{\prime}=a_{ij}^{\prime\prime}$ +\end_inset + +. + Del mismo modo, +\begin_inset Formula $\Delta_{ik}=\Delta_{ik}^{\prime}=\Delta_{ik}^{\prime\prime}$ +\end_inset + + y si +\begin_inset Formula $j\neq k$ +\end_inset + +, +\begin_inset Formula $\Delta_{ij}=\Delta_{ij}^{\prime}+\Delta_{ij}^{\prime\prime}$ +\end_inset + +, por lo que +\begin_inset Formula +\[ +\begin{array}{c} +|A|=a_{11}\Delta_{11}+\dots+a_{1n}\Delta_{1n}=\\ +=a_{11}(\Delta_{11}^{\prime}+\Delta_{11}^{\prime\prime})+\dots+a_{1(k-1)}(\Delta_{1(k-1)}^{\prime}+\Delta_{1(k-1)}^{\prime\prime})+(a_{1k}^{\prime}+a_{1k}^{\prime\prime})\Delta_{1k}+\\ ++a_{1(k+1)}(\Delta_{1(k+1)}^{\prime}+\Delta_{1(k+1)}^{\prime\prime})+\dots+a_{1n}(\Delta_{1n}^{\prime}+\Delta_{1n}^{\prime\prime})=\\ +=a_{11}^{\prime}\Delta_{11}^{\prime}+\dots+a_{1n}\Delta_{1n}^{\prime}+a_{11}^{\prime\prime}\Delta_{11}^{\prime\prime}+\dots+a_{1n}\Delta_{1n}^{\prime\prime}=|A^{\prime}|+|A^{\prime\prime}| +\end{array} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +Alternada: Sea +\begin_inset Formula $A=(a_{ij})=(A_{1},\dots,A_{n})\in M_{n}(K)$ +\end_inset + +. + Si para +\begin_inset Formula $r<s$ +\end_inset + + se tiene que +\begin_inset Formula $A_{r}=A_{s}$ +\end_inset + +, entonces +\begin_inset Formula $a_{r}=a_{s}$ +\end_inset + + y para +\begin_inset Formula $j\neq r,s$ +\end_inset + +, se tiene que +\begin_inset Formula $\Delta_{1j}=0$ +\end_inset + +, pues el menor complementario posee dos columnas iguales, por lo que +\begin_inset Formula $|A|=a_{11}\Delta_{11}+\dots+a_{1n}\Delta_{1n}=a_{1r}\Delta_{1r}+a_{1s}\Delta_{1s}$ +\end_inset + +. + Por otro lado, si llamamos +\begin_inset Formula $A_{j}^{\prime}$ +\end_inset + + al elemento de +\begin_inset Formula $A_{j}$ +\end_inset + + resultado de eliminar +\begin_inset Formula $a_{1j}$ +\end_inset + +, entonces +\begin_inset Formula +\[ +\begin{array}{c} +|A_{1s}|=|(A_{1}^{\prime},\dots,A_{r-1}^{\prime},A_{r}^{\prime},A_{r+1}^{\prime},\dots,A_{s-1}^{\prime},A_{s+1}^{\prime},\dots,A_{n}^{\prime})|=\\ +=-|(A_{1}^{\prime},\dots,A_{r-1}^{\prime},A_{r+1}^{\prime},A_{r}^{\prime},\dots,A_{s-1}^{\prime},A_{s+1}^{\prime},\dots,A_{n}^{\prime})|=\dots=\\ +=(-1)^{s-r-1}|(A_{1}^{\prime},\dots,A_{r-1}^{\prime},A_{r+1}^{\prime},\dots,A_{s-1}^{\prime},A_{r}^{\prime},A_{s+1}^{\prime},\dots,A_{n})|=(-1)^{s-r-1}|A_{1r}| +\end{array} +\] + +\end_inset + +pues +\begin_inset Formula $A_{r}^{\prime}=A_{s}^{\prime}$ +\end_inset + +. + Por tanto +\begin_inset Formula +\[ +\begin{array}{c} +|A|=a_{1r}(-1)^{1+r}|A_{1r}|+a_{1s}(-1)^{1+s}(-1)^{s-r-1}|A_{1r}|=\\ +=a_{1r}|A_{1r}|((-1)^{1+r}+(-1)^{1+2s-r-1})=a_{1r}|A_{1r}|((-1)^{1+r}+(-1)^{-r})=0 +\end{array} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $|I_{n}|=\delta_{11}\Delta_{11}+\dots+\delta_{1n}\Delta_{1n}=\Delta_{11}=(-1)^{1+1}|I_{n-1}|=1$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Se puede probar que, para +\begin_inset Formula $1\leq i\leq n$ +\end_inset + +, cada aplicación dada por +\begin_inset Formula $|A|=a_{i1}\Delta_{i1}+\dots+a_{in}\Delta_{in}$ +\end_inset + +, que llamamos +\series bold +desarrollo del determinante +\series default + de la matriz +\begin_inset Formula $A$ +\end_inset + + por la +\begin_inset Formula $i$ +\end_inset + +-ésima fila, también cumple las condiciones. + Por otro lado, como +\begin_inset Formula $|A|=|A^{t}|$ +\end_inset + +, también se puede desarrollar por filas. + En la práctica se pueden hacer operaciones elementales para obtener ceros + en una fila o columna y luego desarrollar por ella. +\end_layout + +\begin_layout Standard + +\series bold +Determinantes de Vandermonde: +\series default + Restando a cada fila la anterior por +\begin_inset Formula $x_{1}$ +\end_inset + +, desarrollando, dividiendo lo resultante por cada elemento de la primera + fila y repitiendo el proceso, se tiene que: +\begin_inset Formula +\[ +\begin{array}{c} +\left|\begin{array}{cccc} +1 & 1 & \cdots & 1\\ +x_{1} & x_{2} & \cdots & x_{n}\\ +\vdots & \vdots & & \vdots\\ +x_{1}^{n-1} & x_{2}^{n-1} & \cdots & x_{n}^{n-1} +\end{array}\right|=\left|\begin{array}{cccc} +1 & 1 & \cdots & 1\\ +0 & x_{2}-x_{1} & \cdots & x_{n}-x_{1}\\ +\vdots & \vdots & & \vdots\\ +0 & x_{2}^{n-1}-x_{1}x_{2}^{n-2} & \cdots & x_{n}^{n-1}-x_{1}x_{n}^{n-2} +\end{array}\right|=\\ +=(x_{2}-x_{1})\cdots(x_{n}-x_{1})\left|\begin{array}{ccc} +1 & \cdots & 1\\ +x_{2} & \cdots & x_{n}\\ +\vdots & & \vdots\\ +x_{2}^{n-2} & \cdots & x_{n}^{n-2} +\end{array}\right|=\dots=\prod_{1\leq j<i\leq n}(x_{i}-x_{j}) +\end{array} +\] + +\end_inset + + +\end_layout + +\begin_layout Section +Desarrollo de un determinante por menores, de +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +sa +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +rro +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +llo de Laplace +\end_layout + +\begin_layout Standard +Se llama +\series bold +submatriz +\series default + de +\begin_inset Formula $A$ +\end_inset + + a la obtenida al eliminar determinadas filas y columnas de +\begin_inset Formula $A$ +\end_inset + +. + Toda matriz es submatriz de sí misma. + Un +\series bold +menor de orden +\begin_inset Formula $n$ +\end_inset + + +\series default + es el determinante de una submatriz de tamaño +\begin_inset Formula $n\times n$ +\end_inset + +. + Si +\begin_inset Formula $A$ +\end_inset + + es cuadrada, el +\series bold +menor complementario +\series default + +\begin_inset Formula $M^{\prime}$ +\end_inset + + del menor +\begin_inset Formula $M$ +\end_inset + + de +\begin_inset Formula $A$ +\end_inset + + es el determinante de la matriz formada por las filas y columnas restantes. + Un menor es de +\series bold +clase par +\series default + o de +\series bold +clase impar +\series default + según lo sea la suma de los índices de sus filas ( +\begin_inset Formula $i_{1},\dots,i_{p}$ +\end_inset + +) y columnas ( +\begin_inset Formula $j_{1},\dots,j_{p}$ +\end_inset + +). + La +\series bold +signatura +\series default + de un menor +\begin_inset Formula $M$ +\end_inset + + es +\begin_inset Formula $\varepsilon(M)=(-1)^{(i_{1}+\dots+i_{p})+(j_{1}+\dots+j_{p})}$ +\end_inset + +. + Como +\begin_inset Formula $(1+\dots+n)+(1+\dots+n)$ +\end_inset + + es par, todo menor tiene la misma signatura que su complementario. +\end_layout + +\begin_layout Standard +Llamamos +\begin_inset Formula $\chi_{r}$ +\end_inset + + al conjunto de combinaciones de +\begin_inset Formula $r$ +\end_inset + + filas o columnas: +\begin_inset Formula +\[ +\chi_{r}=\{(i_{1},\dots,i_{r}):1\leq i_{1}<\dots<i_{r}\leq n\} +\] + +\end_inset + +Si +\begin_inset Formula $I,J\in\chi_{r}$ +\end_inset + +, llamamos +\begin_inset Formula $A_{IJ}$ +\end_inset + + al menor determinado por las filas +\begin_inset Formula $I$ +\end_inset + + y las columnas +\begin_inset Formula $J$ +\end_inset + + de +\begin_inset Formula $A$ +\end_inset + +. + Entonces: +\end_layout + +\begin_layout Itemize +Dado +\begin_inset Formula $I\in\chi_{r}$ +\end_inset + +, +\begin_inset Formula $|A|=\sum_{J\in\chi_{r}}\varepsilon(A_{IJ})A_{IJ}A_{IJ}^{\prime}$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +Dado +\begin_inset Formula $J\in\chi_{r}$ +\end_inset + +, +\begin_inset Formula $|A|=\sum_{I\in\chi_{r}}\varepsilon(A_{IJ})A_{IJ}A_{IJ}^{\prime}$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Esto es útil cuando +\begin_inset Formula $A$ +\end_inset + + está formada por bloques de tamaño adecuado alguno de los cuales es nulo. + De aquí se tiene que +\begin_inset Formula $\left|\left(\begin{array}{c|c} +P & Q\\ +\hline 0 & R +\end{array}\right)\right|=|P||R|$ +\end_inset + +. +\end_layout + +\begin_layout Section +Determinante de un endomorfismo +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula ${\cal B}$ +\end_inset + + y +\begin_inset Formula ${\cal B}^{\prime}$ +\end_inset + + son bases de +\begin_inset Formula $V$ +\end_inset + + y +\begin_inset Formula $f\in\text{End}(V)$ +\end_inset + +, entonces +\begin_inset Formula +\[ +M_{{\cal B}}(f)=M_{{\cal B}{\cal B}^{\prime}}M_{{\cal B}^{\prime}}(f)M_{{\cal B}^{\prime}{\cal B}}=P^{-1}M_{{\cal B}^{\prime}}(f)P +\] + +\end_inset + +por lo que +\begin_inset Formula $|M_{{\cal B}}(f)|=|P|^{-1}|M_{{\cal B}^{\prime}}(f)||P|=|M_{{\cal B}^{\prime}}(f)|$ +\end_inset + +. + Así, llamamos +\series bold +determinante del endomorfismo +\begin_inset Formula $f$ +\end_inset + + +\series default + al de la matriz asociada a +\begin_inset Formula $f$ +\end_inset + + respecto de cualquier base de +\begin_inset Formula $V$ +\end_inset + +. +\end_layout + +\begin_layout Section +Matriz adjunta. + Aplicación al cálculo de la inversa +\end_layout + +\begin_layout Standard +Llamamos +\series bold +matriz adjunta +\series default + de +\begin_inset Formula $A$ +\end_inset + + a la matriz +\begin_inset Formula $\hat{A}=(\Delta_{ij})\in M_{n}(K)$ +\end_inset + +. + +\series bold +Teorema: +\series default + Si +\begin_inset Formula $A\in M_{n}(K)$ +\end_inset + +, entonces +\begin_inset Formula $A\cdot\hat{A}^{t}=\hat{A}^{t}\cdot A=|A|I_{n}$ +\end_inset + +. + +\series bold +Demostración: +\series default + Si +\begin_inset Formula $A=(a_{ij})$ +\end_inset + +, +\begin_inset Formula $\hat{A}=(\Delta_{ij})$ +\end_inset + + y +\begin_inset Formula $\hat{A}^{t}=(b_{ij})$ +\end_inset + +, entonces +\begin_inset Formula $b_{ij}=\Delta_{ji}$ +\end_inset + +. + Sea entonces +\begin_inset Formula $C=(c_{ij})=A\cdot\hat{A}^{t}$ +\end_inset + +, entonces +\begin_inset Formula $c_{ij}=\sum_{k=1}^{n}a_{ik}b_{kj}=\sum_{k=1}^{n}a_{ik}\Delta_{jk}$ +\end_inset + +. + Para +\begin_inset Formula $i\neq j$ +\end_inset + +, esto corresponde al desarrollo por la fila +\begin_inset Formula $j$ +\end_inset + +-ésima del determinante de la matriz que se diferencia de +\begin_inset Formula $A$ +\end_inset + + en que tiene la fila +\begin_inset Formula $i$ +\end_inset + +-ésima copiada en la +\begin_inset Formula $j$ +\end_inset + +-ésima, por lo que entonces +\begin_inset Formula $c_{ij}=0$ +\end_inset + +. + Si +\begin_inset Formula $i\neq j$ +\end_inset + +, este es el desarrollo por la fila +\begin_inset Formula $j$ +\end_inset + +-ésima de +\begin_inset Formula $A$ +\end_inset + +, por lo que +\begin_inset Formula $c_{ii}=|A|$ +\end_inset + + y +\begin_inset Formula $C=|A|I_{n}$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Como consecuencia, se tiene el +\series bold +teorema +\series default + de que +\begin_inset Formula $A$ +\end_inset + + es invertible si y sólo si +\begin_inset Formula $|A|\neq0$ +\end_inset + + y entonces +\begin_inset Formula +\[ +A^{-1}=\frac{1}{|A|}\hat{A}^{t} +\] + +\end_inset + + +\end_layout + +\begin_layout Section +Cálculo del rango de una matriz por determinantes +\end_layout + +\begin_layout Standard +El rango de +\begin_inset Formula $A$ +\end_inset + + es el mayor de los órdenes de los menores no nulos de +\begin_inset Formula $A$ +\end_inset + +. + +\series bold +Demostración: +\series default + Sean +\begin_inset Formula $A=(a_{ij})\in M_{m,n}(K)$ +\end_inset + + con +\begin_inset Formula $A\neq0$ +\end_inset + +, +\begin_inset Formula $r=\text{rang}(A)$ +\end_inset + + y +\begin_inset Formula $p$ +\end_inset + + el mayor de los tamaños de los menores no nulos, que existe si +\begin_inset Formula $A\neq0$ +\end_inset + +. + Si +\begin_inset Formula $A^{\prime}$ +\end_inset + + es una submatriz cuadrada de +\begin_inset Formula $A$ +\end_inset + + de tamaño +\begin_inset Formula $p\times p$ +\end_inset + + con +\begin_inset Formula $|A^{\prime}|\neq0$ +\end_inset + +, entonces la submatriz +\begin_inset Formula $B$ +\end_inset + + formada por las filas de +\begin_inset Formula $A^{\prime}$ +\end_inset + + pero con todas las columnas de +\begin_inset Formula $A$ +\end_inset + + tiene +\begin_inset Formula $p$ +\end_inset + + columnas linealmente independientes (las de +\begin_inset Formula $A^{\prime}$ +\end_inset + +) y por tanto también tiene +\begin_inset Formula $p$ +\end_inset + + filas linealmente independientes, pero entonces +\begin_inset Formula $A$ +\end_inset + + tiene al menos +\begin_inset Formula $p$ +\end_inset + + filas linealmente independientes y +\begin_inset Formula $r\geq p$ +\end_inset + +. + Por otro lado, si +\begin_inset Formula $A_{i_{1}},\dots,A_{i_{r}}$ +\end_inset + + son filas linealmente independientes de +\begin_inset Formula $A$ +\end_inset + + y tomamos la submatriz +\begin_inset Formula $B\in M_{r,n}(K)$ +\end_inset + + formada por estas filas y todas las columnas, +\begin_inset Formula $B$ +\end_inset + + tendrá rango +\begin_inset Formula $r$ +\end_inset + +, luego tendrá +\begin_inset Formula $r$ +\end_inset + + columnas +\begin_inset Formula $j_{1},\dots,j_{r}$ +\end_inset + + linealmente independientes. + Si tomamos la submatriz +\begin_inset Formula $A^{\prime}\in M_{r}(K)$ +\end_inset + + formada por estas columnas, al ser linealmente independientes, +\begin_inset Formula $|A^{\prime}|\neq0$ +\end_inset + +, luego +\begin_inset Formula $p\geq r$ +\end_inset + +. + Por tanto +\begin_inset Formula $p=r$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Dados +\begin_inset Formula $A_{i}=(a_{1i},\dots,a_{ni})\in K^{n}$ +\end_inset + + con +\begin_inset Formula $A_{1},\dots,A_{r}$ +\end_inset + + linealmente independientes y +\begin_inset Formula +\[ +\left|\begin{array}{ccc} +a_{i_{1}1} & \cdots & a_{i_{1}r}\\ +\vdots & \ddots & \vdots\\ +a_{i_{r}1} & \cdots & a_{i_{r}r} +\end{array}\right|\neq0 +\] + +\end_inset + + +\begin_inset Formula $B=(b_{1},\dots,b_{n})$ +\end_inset + + es combinación lineal de +\begin_inset Formula $A_{1},\dots,A_{r}$ +\end_inset + + si y sólo si para todo +\begin_inset Formula $j$ +\end_inset + +, +\begin_inset Formula +\[ +\left|\begin{array}{cccc} +a_{i_{1}1} & \dots & a_{i_{1}r} & b_{i_{1}}\\ +\vdots & \ddots & \vdots & \vdots\\ +a_{i_{r}1} & \cdots & a_{i_{r}r} & b_{i_{r}}\\ +a_{j1} & \cdots & a_{jr} & b_{j} +\end{array}\right|=0 +\] + +\end_inset + + +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\implies]$ +\end_inset + + +\end_layout + +\end_inset + +Si son linealmente dependientes, los determinantes son nulos. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\impliedby]$ +\end_inset + + +\end_layout + +\end_inset + +Si todos son nulos, desarrollando por la última fila, se obtiene, para cada + +\begin_inset Formula $j$ +\end_inset + +, que +\begin_inset Formula +\[ +a_{j1}\left|\begin{array}{cccc} +a_{i_{1}2} & \cdots & a_{i_{1}r} & b_{i_{1}}\\ +\vdots & \ddots & \vdots & \vdots\\ +a_{i_{r}2} & \cdots & a_{i_{r}r} & b_{i_{r}} +\end{array}\right|\pm\dots\pm b_{j}\left|\begin{array}{ccc} +a_{i_{1}1} & \cdots & a_{i_{1}r}\\ +\vdots & \ddots & \vdots\\ +a_{i_{r}1} & \cdots & a_{i_{r}r} +\end{array}\right|=0 +\] + +\end_inset + +Por lo que +\begin_inset Formula +\[ +b_{j}=\frac{1}{\left|\begin{array}{ccc} +a_{i_{1}1} & \cdots & a_{i_{1}r}\\ +\vdots & \ddots & \vdots\\ +a_{i_{r}1} & \cdots & a_{i_{r}r} +\end{array}\right|}\left(\pm a_{j1}\left|\begin{array}{ccc} +a_{i_{1}2} & \cdots & b_{i_{1}}\\ +\vdots & \ddots & \vdots\\ +a_{i_{r}2} & \cdots & b_{i_{r}} +\end{array}\right|\pm\dots\pm a_{j_{r}}\left|\begin{array}{ccc} +a_{i_{1}1} & \cdots & b_{i1}\\ +\vdots & \ddots & \vdots\\ +a_{i_{r}1} & \cdots & b_{i_{r}} +\end{array}\right|\right) +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +A efectos prácticos, esto significa que, una vez encontrado un menor no + nulo de orden +\begin_inset Formula $k$ +\end_inset + + en una matriz +\begin_inset Formula $A$ +\end_inset + +, podemos +\emph on +orlarlo +\emph default + (obtener otro añadiendo una fila y una columna a la submatriz) de todas + las formas posibles y, si todos los menores resultantes son nulos, entonces + +\begin_inset Formula $\text{rang}(A)=k$ +\end_inset + +. +\end_layout + +\begin_layout Section +Regla de Cramer +\end_layout + +\begin_layout Standard +Un sistema de ecuaciones lineales +\begin_inset Formula $AX=B$ +\end_inset + + es un +\series bold +sistema de Cramer +\series default + si +\begin_inset Formula $A$ +\end_inset + + es invertible. + En tal caso tiene solución única +\begin_inset Formula $X=A^{-1}B$ +\end_inset + +. + +\series bold +Regla de Cramer: +\series default + si las columnas de +\begin_inset Formula $A$ +\end_inset + + son +\begin_inset Formula $(A_{1},\dots,A_{n})$ +\end_inset + +, entonces +\begin_inset Formula +\[ +x_{i}=\frac{\det(A_{1},\dots,A_{i-1},B,A_{i+1},\dots,A_{n})}{\det(A)} +\] + +\end_inset + + +\series bold +Demostración: +\series default + +\begin_inset Formula $A^{-1}=\frac{1}{|A|}\hat{A}^{t}$ +\end_inset + +, y si +\begin_inset Formula $X=(x_{i})$ +\end_inset + +, +\begin_inset Formula $A=(a_{ij})$ +\end_inset + + y +\begin_inset Formula $\hat{A}=(\Delta_{ij})$ +\end_inset + +, entonces +\begin_inset Formula $x_{i}=\sum_{j=1}^{n}\frac{1}{|A|}\Delta_{ji}b_{j}=\frac{1}{|A|}\sum_{j=1}^{n}\Delta_{ji}b_{j}$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $A\in M_{m,n}(K)$ +\end_inset + + con +\begin_inset Formula $\text{rang}(A)=r$ +\end_inset + +, habrá un menor +\begin_inset Formula $M\neq0$ +\end_inset + + de orden +\begin_inset Formula $r$ +\end_inset + +, por lo que las +\begin_inset Formula $n-r$ +\end_inset + + últimas filas serán combinaciones lineales de las +\begin_inset Formula $r$ +\end_inset + + primeras, y moviendo al lado derecho los +\begin_inset Formula $m-r$ +\end_inset + + coeficientes que no están en la submatriz de +\begin_inset Formula $M$ +\end_inset + +, nos queda el sistema +\begin_inset Formula +\[ +\left.\begin{array}{ccc} +a_{11}x_{1}+\dots+a_{1r}x_{r} & = & b_{1}-(a_{1r+1}x_{r+1}+\dots+a_{1n}x_{n})\\ + & \vdots\\ +a_{r1}x_{1}+\dots+a_{rr}x_{r} & = & b_{r}-(a_{rr+1}x_{r+1}+\dots+a_{rn}x_{n}) +\end{array}\right\} +\] + +\end_inset + +que podemos resolver por Cramer. +\end_layout + +\end_body +\end_document diff --git a/algl/n5.lyx b/algl/n5.lyx new file mode 100644 index 0000000..bb844d5 --- /dev/null +++ b/algl/n5.lyx @@ -0,0 +1,1323 @@ +#LyX 2.3 created this file. For more info see http://www.lyx.org/ +\lyxformat 544 +\begin_document +\begin_header +\save_transient_properties true +\origin unavailable +\textclass book +\use_default_options true +\maintain_unincluded_children false +\language spanish +\language_package default +\inputencoding auto +\fontencoding global +\font_roman "default" "default" +\font_sans "default" "default" +\font_typewriter "default" "default" +\font_math "auto" "auto" +\font_default_family default +\use_non_tex_fonts false +\font_sc false +\font_osf false +\font_sf_scale 100 100 +\font_tt_scale 100 100 +\use_microtype false +\use_dash_ligatures true +\graphics default +\default_output_format default +\output_sync 0 +\bibtex_command default +\index_command default +\paperfontsize default +\spacing single +\use_hyperref false +\papersize default +\use_geometry false +\use_package amsmath 1 +\use_package amssymb 1 +\use_package cancel 1 +\use_package esint 1 +\use_package mathdots 1 +\use_package mathtools 1 +\use_package mhchem 1 +\use_package stackrel 1 +\use_package stmaryrd 1 +\use_package undertilde 1 +\cite_engine basic +\cite_engine_type default +\biblio_style plain +\use_bibtopic false +\use_indices false +\paperorientation portrait +\suppress_date false +\justification true +\use_refstyle 1 +\use_minted 0 +\index Index +\shortcut idx +\color #008000 +\end_index +\secnumdepth 3 +\tocdepth 3 +\paragraph_separation indent +\paragraph_indentation default +\is_math_indent 0 +\math_numbering_side default +\quotes_style swiss +\dynamic_quotes 0 +\papercolumns 1 +\papersides 1 +\paperpagestyle default +\tracking_changes false +\output_changes false +\html_math_output 0 +\html_css_as_file 0 +\html_be_strict false +\end_header + +\begin_body + +\begin_layout Section +Semejanza de matrices +\end_layout + +\begin_layout Standard +\begin_inset Formula $A,B\in M_{n}(K)$ +\end_inset + + son +\series bold +semejantes +\series default + si +\begin_inset Formula $\exists P\in M_{n}(K):B=P^{-1}AP$ +\end_inset + +. + Esta relación es de equivalencia, y si dos matrices son semejantes también + son equivalentes y por tanto tienen el mismo rango, si bien el recíproco + no se cumple. +\end_layout + +\begin_layout Standard +Sea +\begin_inset Formula $A\in M_{n}(K)$ +\end_inset + + una matriz formada por +\series bold +bloques +\series default + cuadrados en la diagonal y ceros en el resto: +\begin_inset Formula +\[ +A=\left(\begin{array}{ccc} +\boxed{A_{1}} & & 0\\ + & \ddots\\ +0 & & \boxed{A_{t}} +\end{array}\right) +\] + +\end_inset + +con +\begin_inset Formula $A_{i}\in M_{n_{i}}(K)$ +\end_inset + + y +\begin_inset Formula $n_{1}+\dots+n_{t}=n$ +\end_inset + +. + Por el desarrollo de Laplace, su determinante es +\begin_inset Formula $|A|=|A_{1}|\cdots|A_{t}|$ +\end_inset + +; su rango es la suma de los rangos de los +\begin_inset Formula $A_{i}$ +\end_inset + +, y su potencia +\begin_inset Formula $k$ +\end_inset + +-ésima es +\begin_inset Formula +\[ +A^{k}=\left(\begin{array}{ccc} +\boxed{A_{1}^{k}} & & 0\\ + & \ddots\\ +0 & & \boxed{A_{t}^{k}} +\end{array}\right) +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Entonces, si +\begin_inset Formula $B$ +\end_inset + + es semejante a +\begin_inset Formula $A$ +\end_inset + +, +\begin_inset Formula $|B|=|P^{-1}AP|=|P|^{-1}|A||P|=|A|$ +\end_inset + +, su rango es el de +\begin_inset Formula $A$ +\end_inset + + y +\begin_inset Formula +\[ +B^{k}=\underset{k\text{ veces}}{(P^{-1}AP)\cdots(P^{-1}AP)}=P^{-1}A^{k}P +\] + +\end_inset + + +\end_layout + +\begin_layout Section +Subespacios invariantes +\end_layout + +\begin_layout Standard +Dado +\begin_inset Formula $f\in\text{End}_{K}(V)$ +\end_inset + + y +\begin_inset Formula $W\leq V$ +\end_inset + +, +\begin_inset Formula $W$ +\end_inset + + es +\series bold +invariante +\series default + por +\begin_inset Formula $f$ +\end_inset + + si +\begin_inset Formula $f(W)\subseteq W$ +\end_inset + +. + Entonces la restricción de +\begin_inset Formula $f$ +\end_inset + + a +\begin_inset Formula $W$ +\end_inset + + es +\begin_inset Formula $f|_{W}\in\text{End}_{K}(W)$ +\end_inset + +. + También se tiene que +\begin_inset Formula $\{0\}$ +\end_inset + + y +\begin_inset Formula $V$ +\end_inset + + son invariantes de cada +\begin_inset Formula $f\in\text{End}_{K}(V)$ +\end_inset + +, y la suma e intersección de subespacios invariantes por +\begin_inset Formula $f$ +\end_inset + + también son subespacios invariantes por +\begin_inset Formula $f$ +\end_inset + +. + Ahora supongamos que +\begin_inset Formula $V=W_{1}\oplus\dots\oplus W_{t}$ +\end_inset + +, donde cada +\begin_inset Formula $W_{i}$ +\end_inset + + es un subespacio invariante no nulo por +\begin_inset Formula $f\in\text{End}(V)$ +\end_inset + +. + Si tomamos +\begin_inset Formula ${\cal B}={\cal B}_{1}\cup\dots\cup{\cal B}_{t}$ +\end_inset + +, siendo cada +\begin_inset Formula ${\cal B}_{i}$ +\end_inset + + una base de +\begin_inset Formula $W_{i}$ +\end_inset + +, entonces +\begin_inset Formula +\[ +M_{{\cal B}}(f)=\left(\begin{array}{ccc} +\boxed{A_{1}} & & 0\\ + & \ddots\\ +0 & & \boxed{A_{t}} +\end{array}\right) +\] + +\end_inset + +donde +\begin_inset Formula $A_{i}=M_{{\cal B}_{i}}(f|_{W})\in M_{n_{i}}(K)$ +\end_inset + + para +\begin_inset Formula $n_{i}=\dim(W_{i})$ +\end_inset + +. + Recíprocamente, si +\begin_inset Formula $M_{{\cal B}}(f)$ +\end_inset + + tiene dicha forma y +\begin_inset Formula +\[ +{\cal B}=\{v_{1},\dots,v_{n_{1}},v_{n_{1}+1},\dots,v_{n_{1}+n_{2}},\dots,v_{n_{1}+\dots+n_{t-1}+1},\dots,v_{n_{1}+\dots+n_{t}}\} +\] + +\end_inset + +entonces +\begin_inset Formula $W_{1}=<v_{1},\dots,v_{n_{1}}>$ +\end_inset + +, +\begin_inset Formula $W_{2}=<v_{n_{1}+1},\dots,v_{n_{1}+n_{2}}>$ +\end_inset + +, etc. + son subespacios vectoriales invariantes por +\begin_inset Formula $f$ +\end_inset + +. +\end_layout + +\begin_layout Section +Endomorfismos y matrices diagonalizables +\end_layout + +\begin_layout Standard +\begin_inset Formula $f\in\text{End}_{K}(V)$ +\end_inset + + es +\series bold +diagonalizable +\series default + si existe una base +\begin_inset Formula ${\cal B}$ +\end_inset + + de +\begin_inset Formula $V$ +\end_inset + + tal que +\begin_inset Formula $M_{{\cal B}}(f)$ +\end_inset + + es diagonal, y una matriz cuadrada es diagonalizable si lo es el endomorfismo + de +\begin_inset Formula $K^{n}$ +\end_inset + + que cuya matriz respecto a la base canónica es +\begin_inset Formula $A$ +\end_inset + +. + Equivalentemente, una matriz cuadrada es diagonalizable si y sólo si es + semejante a una matriz diagonal, y un endomorfismo es diagonalizable si + su matriz asociada respecto a cualquier base lo es. + Denotamos las matrices diagonales como +\begin_inset Formula +\[ +\left(\begin{array}{ccc} +\lambda_{1} & & 0\\ + & \ddots\\ +0 & & \lambda_{n} +\end{array}\right)=\text{Diag}(\lambda_{1},\dots,\lambda_{n}) +\] + +\end_inset + + +\end_layout + +\begin_layout Section +Vectores y valores propios +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula ${\cal B}=\{u_{1,}\dots,u_{n}\}$ +\end_inset + + y +\begin_inset Formula $M_{{\cal B}}(f)=\text{Diag}(\lambda_{1},\dots,\lambda_{n})$ +\end_inset + +, se tiene que +\begin_inset Formula $f(u_{i})=\lambda_{1}u_{1}$ +\end_inset + +. + Así: +\end_layout + +\begin_layout Itemize +Un +\series bold +vector propio +\series default +, +\series bold +autovector +\series default + o +\series bold +vector característico +\series default + de +\begin_inset Formula $f$ +\end_inset + + es un vector +\begin_inset Formula $v\neq0$ +\end_inset + + para el que existe un +\begin_inset Formula $\lambda\in K$ +\end_inset + + con +\begin_inset Formula $f(v)=\lambda v$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +Un +\series bold +valor propio +\series default +, +\series bold +autovalor +\series default + o +\series bold +valor característico +\series default + de +\begin_inset Formula $f$ +\end_inset + + es un escalar +\begin_inset Formula $\lambda\in K$ +\end_inset + + para el que existe un +\begin_inset Formula $v\in V\backslash\{0\}$ +\end_inset + + tal que +\begin_inset Formula $f(v)=\lambda v$ +\end_inset + +. + Decimos que +\begin_inset Formula $\lambda$ +\end_inset + + es +\series bold +\emph on +el +\emph default + valor propio asociado al vector propio +\begin_inset Formula $v$ +\end_inset + + +\series default +, o que +\begin_inset Formula $v$ +\end_inset + + es +\series bold +\emph on +un +\emph default + vector propio asociado al valor propio +\begin_inset Formula $\lambda$ +\end_inset + + +\series default +. +\end_layout + +\begin_layout Standard +Así, +\begin_inset Formula $f\in\text{End}(V)$ +\end_inset + + es diagonalizable si y sólo si existe una base de +\begin_inset Formula $V$ +\end_inset + + formada por vectores propios de +\begin_inset Formula $f$ +\end_inset + +. +\end_layout + +\begin_layout Section +Subespacios propios. + Polinomio característico +\end_layout + +\begin_layout Standard +Los vectores propios de +\begin_inset Formula $f$ +\end_inset + + asociados a +\begin_inset Formula $\lambda$ +\end_inset + + son todos los vectores no nulos de +\begin_inset Formula $\text{Nuc}(f-\lambda Id)$ +\end_inset + +. + Así, +\begin_inset Formula $V_{\lambda}=\text{Nuc}(f-\lambda Id)=\{v\in V:(f-\lambda Id)(v)=0\}=\{v\in V:f(v)=\lambda v\}$ +\end_inset + + es el +\series bold +subespacio propio +\series default + o +\series bold +característico +\series default + correspondiente al valor propio +\begin_inset Formula $\lambda$ +\end_inset + +. + Así, +\begin_inset Formula $\lambda\in K$ +\end_inset + + es un valor propio de +\begin_inset Formula $f$ +\end_inset + + si y sólo si +\begin_inset Formula $\det(f-\lambda Id)=0$ +\end_inset + +. + +\series bold +Demostración: +\series default + +\begin_inset Formula $\lambda\in K$ +\end_inset + + es valor propio si y sólo si existe +\begin_inset Formula $0\neq v\in V_{\lambda}$ +\end_inset + +, es decir, si +\begin_inset Formula $\text{Nuc}(f-\lambda Id)\neq\{0\}$ +\end_inset + +, pero entonces +\begin_inset Formula $0<\dim(\text{Nuc}(\lambda Id-f))=\dim(V)-\text{rang}(\lambda Id-f)$ +\end_inset + +, es decir, +\begin_inset Formula $\text{rang}(\lambda Id-f)<\dim(V)$ +\end_inset + + o, equivalentemente, +\begin_inset Formula $\det(\lambda Id-f)=0$ +\end_inset + +. +\end_layout + +\begin_layout Standard +\begin_inset Formula $P_{f}(x):=\det(xId-f)$ +\end_inset + + es el +\series bold +polinomio característico +\series default + de +\series bold + +\begin_inset Formula $f$ +\end_inset + + +\series default +, y +\begin_inset Formula $P_{A}(x):=\det(xI_{n}-A)$ +\end_inset + + es el polinomio característico de +\begin_inset Formula $A$ +\end_inset + +. + Podemos comprobar que +\begin_inset Formula +\[ +P_{A}(x)=x^{n}-\text{tr}(A)x^{n-1}+\dots+(-1)^{n}\det(A) +\] + +\end_inset + +donde +\begin_inset Formula $\text{tr}(A)$ +\end_inset + + es la +\series bold +traza +\series default + de +\begin_inset Formula $A$ +\end_inset + +, la suma de los elementos de su diagonal. + Obtenemos como resultado que los valores propios de +\begin_inset Formula $f\in\text{End}(V)$ +\end_inset + + son las raíces de +\begin_inset Formula $P_{f}(x)$ +\end_inset + +, y que +\begin_inset Formula $f$ +\end_inset + + tiene a lo sumo +\begin_inset Formula $\dim(V)$ +\end_inset + + valores propios distintos. +\end_layout + +\begin_layout Section +Independencia de los subespacios propios +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $\lambda_{1},\dots,\lambda_{s}$ +\end_inset + + son valores propios de +\begin_inset Formula $f$ +\end_inset + + distintos dos a dos, entonces +\begin_inset Formula $\text{Nuc}(\lambda_{1}Id-f)+\dots+\text{Nuc}(\lambda_{s}Id-f)$ +\end_inset + + es suma directa, y en particular, vectores propios correspondientes a valores + propios distintos dos a dos son linealmente independientes. + +\series bold +Demostración: +\series default + Para +\begin_inset Formula $s=2$ +\end_inset + +, sean +\begin_inset Formula $v_{1}\in\text{Nuc}(\lambda_{1}Id-f)$ +\end_inset + + y +\begin_inset Formula $v_{2}\in\text{Nuc}(\lambda_{2}Id-f)$ +\end_inset + + con +\begin_inset Formula $0=v_{1}+v_{2}$ +\end_inset + +. + Entonces +\begin_inset Formula $0=f(0)=f(v_{1}+v_{2})=f(v_{1})+f(v_{2})=\lambda_{1}v_{1}+\lambda_{2}v_{2}$ +\end_inset + +, pero también +\begin_inset Formula $0=\lambda_{2}(v_{1}+v_{2})=\lambda_{2}v_{1}+\lambda_{2}v_{2}$ +\end_inset + +. + Restando, +\begin_inset Formula $0=(\lambda_{2}-\lambda_{1})v_{1}$ +\end_inset + +, pero como +\begin_inset Formula $\lambda_{2}\neq\lambda_{1}$ +\end_inset + +, entonces +\begin_inset Formula $v_{1}=0$ +\end_inset + + y por tanto +\begin_inset Formula $v_{2}$ +\end_inset + + también. + Ahora sea +\begin_inset Formula $s>2$ +\end_inset + + y supongamos el resultado cierto para +\begin_inset Formula $s-1$ +\end_inset + +. + Sean ahora +\begin_inset Formula $v_{1}\in\text{Nuc}(\lambda_{1}Id-f),\dots,v_{s}\in\text{Nuc}(\lambda_{s}Id-f)$ +\end_inset + + con +\begin_inset Formula $0=v_{1}+\dots+v_{s}$ +\end_inset + +, entonces +\begin_inset Formula $0=f(0)=f(v_{1}+\dots+v_{s})=f(v_{1})+\dots+f(v_{s})=\lambda_{1}v_{1}+\dots+\lambda_{s}v_{s}$ +\end_inset + +, pero también +\begin_inset Formula $0=\lambda_{s}v_{1}+\dots+\lambda_{s}v_{k-1}+\lambda_{s}v_{s}$ +\end_inset + +. + Restando, +\begin_inset Formula $0=(\lambda_{s}-\lambda_{1})v_{1}+\dots+(\lambda_{s}-\lambda_{s-1})v_{s-1}$ +\end_inset + +. + Aplicando la hipótesis de inducción, queda que +\begin_inset Formula $v_{1}=\dots=v_{s-1}=0$ +\end_inset + +, luego +\begin_inset Formula $v_{s}=0$ +\end_inset + +. +\end_layout + +\begin_layout Standard +También, si +\begin_inset Formula $f\in\text{End}(V)$ +\end_inset + + tiene +\begin_inset Formula $\dim(V)$ +\end_inset + + autovalores, entonces es diagonalizable. +\series bold + +\begin_inset Newline newline +\end_inset + +Demostración: +\series default + Si +\begin_inset Formula $\lambda_{1},\dots,\lambda_{n}$ +\end_inset + + son valores propios de +\begin_inset Formula $f$ +\end_inset + + distintos dos a dos y +\begin_inset Formula $v_{1},\dots,v_{n}$ +\end_inset + + son vectores propios asociados a cada uno, entonces +\begin_inset Formula $v_{1},\dots,v_{n}$ +\end_inset + + son +\begin_inset Formula $n$ +\end_inset + + vectores linealmente independientes en un espacio de dimensión +\begin_inset Formula $n$ +\end_inset + +, por lo que constituyen una base formada por vectores propios de +\begin_inset Formula $f$ +\end_inset + +. +\end_layout + +\begin_layout Section +Caracterización de los endomorfismos diagonalizables +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $P(x)$ +\end_inset + + es un polinomio con coeficientes en +\begin_inset Formula $K$ +\end_inset + + y +\begin_inset Formula $\lambda\in K$ +\end_inset + + es una raíz de +\begin_inset Formula $P(x)$ +\end_inset + +, entonces +\begin_inset Formula $\lambda$ +\end_inset + + tiene +\series bold +multiplicidad +\series default + +\begin_inset Formula $m$ +\end_inset + + en +\begin_inset Formula $P(x)$ +\end_inset + + si +\begin_inset Formula $(x-\lambda)^{m}|P(x)$ +\end_inset + + pero +\begin_inset Formula $\neg((x-\lambda)^{m+1}|P(x))$ +\end_inset + +. + Si una raíz tiene multiplicidad 1, es una raíz +\series bold +simple +\series default +\SpecialChar endofsentence + De lo contrario es una raíz +\series bold + múltiple +\series default +\SpecialChar endofsentence + +\end_layout + +\begin_layout Standard +Dado +\begin_inset Formula $f\in\text{End}_{K}(V)$ +\end_inset + + y +\begin_inset Formula $\lambda$ +\end_inset + + un valor propio de +\begin_inset Formula $f$ +\end_inset + +, si +\begin_inset Formula $d=\dim(\text{Nuc}(\lambda Id-f))$ +\end_inset + + y +\begin_inset Formula $m$ +\end_inset + + es la multiplicidad de +\begin_inset Formula $\lambda$ +\end_inset + + en +\begin_inset Formula $P_{f}(x)$ +\end_inset + +, entonces +\begin_inset Formula $d\leq m$ +\end_inset + +. + En particular, si el valor propio es una raíz simple, entonces +\begin_inset Formula $d=m=1$ +\end_inset + +. + +\series bold +Demostración: +\series default + Sea +\begin_inset Formula $\{v_{1},\dots,v_{d}\}$ +\end_inset + + una base de +\begin_inset Formula $\text{Nuc}(\lambda Id-f)$ +\end_inset + + y +\begin_inset Formula ${\cal B}=\{v_{1},\dots,v_{d},v_{d+1},\dots,v_{n}\}$ +\end_inset + + una base de +\begin_inset Formula $V$ +\end_inset + +. + Entonces +\begin_inset Formula $M_{{\cal B}}(f)$ +\end_inset + + tiene forma +\begin_inset Formula +\[ +\left(\begin{array}{ccc|c} +\lambda & & 0\\ + & \ddots & & C\\ +0 & & \lambda\\ +\hline & & \\ + & 0 & & D\\ + & & \\ +\end{array}\right) +\] + +\end_inset + +por lo que +\begin_inset Formula $P_{f}(x)=(x-\lambda)^{d}\det(xI_{n-d}-D)=(x-\lambda)^{d}Q(x)$ +\end_inset + +, por lo que +\begin_inset Formula $d\leq m$ +\end_inset + +. +\end_layout + +\begin_layout Standard + +\series bold +Teorema de diagonalización: +\series default + +\begin_inset Formula $f$ +\end_inset + + es diagonalizable si y sólo si +\begin_inset Formula +\[ +P_{f}(x)=(x-\lambda_{1})^{d_{1}}\cdots(x-\lambda_{r})^{d_{r}} +\] + +\end_inset + +con +\begin_inset Formula $\lambda_{1},\dots,\lambda_{r}\in K$ +\end_inset + + distintos dos a dos, y +\begin_inset Formula $d_{i}=\dim(\text{Nuc}(\lambda_{i}Id-f))$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\implies]$ +\end_inset + + +\end_layout + +\end_inset + +Sean +\begin_inset Formula $\lambda_{1},\dots,\lambda_{r}$ +\end_inset + + los valores propios de +\begin_inset Formula $f$ +\end_inset + +, existirá una base +\begin_inset Formula ${\cal B}$ +\end_inset + + de vectores propios en los que cada vector tendrá asociado un valor propio + y pertenecerá por tanto al subespacio propio correspondiente. + Agrupando, +\begin_inset Formula $M_{{\cal B}}(f)$ +\end_inset + + tendrá forma +\begin_inset Formula +\[ +\left(\begin{array}{ccccccc} +\lambda_{1}\\ + & \ddots & & & & 0\\ + & & \lambda_{1}\\ + & & & \ddots\\ + & & & & \lambda_{r}\\ + & 0 & & & & \ddots\\ + & & & & & & \lambda_{r} +\end{array}\right) +\] + +\end_inset + +donde cada +\begin_inset Formula $\lambda_{i}$ +\end_inset + + se repetirá +\begin_inset Formula $m_{i}$ +\end_inset + + veces, el número de vectores propios de la base del subespacio. + Por tanto, +\begin_inset Formula $P_{f}(x)=(x-\lambda_{1})^{m_{1}}\cdots(x-\lambda_{r})^{m_{r}}$ +\end_inset + + tiene todas sus raíces en +\begin_inset Formula $K$ +\end_inset + +. + Además, si +\begin_inset Formula $d_{i}=\dim(\text{Nuc}(\lambda_{i}Id-f))$ +\end_inset + +, se tiene que +\begin_inset Formula $\sum d_{i}=\dim(\text{Nuc}(\lambda_{1}Id-f)\oplus\cdots\oplus\text{Nuc}(\lambda_{r}Id-f))\leq\dim(V)=n$ +\end_inset + +, y como en la base hay +\begin_inset Formula $m_{i}$ +\end_inset + + vectores linealmente independientes de +\begin_inset Formula $\text{Nuc}(\lambda_{i}Id-f)$ +\end_inset + +, entonces +\begin_inset Formula $m_{i}\leq d_{i}$ +\end_inset + +, luego +\begin_inset Formula $n=\text{gr}(P_{f}(x))=\sum m_{i}\leq\sum d_{i}\leq n$ +\end_inset + + y por tanto +\begin_inset Formula $m_{i}=d_{i}$ +\end_inset + +. +\end_layout + +\begin_layout Itemize +\begin_inset Argument item:1 +status open + +\begin_layout Plain Layout +\begin_inset Formula $\impliedby]$ +\end_inset + + +\end_layout + +\end_inset + +Si +\begin_inset Formula $P_{f}(x)=(x-\lambda_{1})^{d_{1}}\cdots(x-\lambda_{r})^{d_{r}}$ +\end_inset + + con +\begin_inset Formula $d_{i}=\dim(\text{Nuc}(f-\lambda Id))$ +\end_inset + +, entonces +\begin_inset Formula $\dim(\text{Nuc}(\lambda_{1}Id-f)\oplus\cdots\oplus\text{Nuc}(\lambda_{r}Id-f))=d_{1}+\dots+d_{r}=\text{gr}(P_{f}(x))=\dim(V)$ +\end_inset + +, luego +\begin_inset Formula $V=\text{Nuc}(f-\lambda_{1}Id)\oplus\cdots\oplus\text{Nuc}(f-\lambda_{r}Id)$ +\end_inset + + y la unión de las bases de cada subespacio será una base de +\begin_inset Formula $V$ +\end_inset + + formada por vectores propios. +\end_layout + +\begin_layout Standard +Así, para diagonalizar una matriz +\begin_inset Formula $A\in M_{n}(K)$ +\end_inset + + en matrices +\begin_inset Formula $A=M_{{\cal CB}}DM_{{\cal BC}}$ +\end_inset + +, con +\begin_inset Formula $D$ +\end_inset + + diagonal, obtenemos su polinomio característico, hallamos sus raíces, que + serán los autovalores de +\begin_inset Formula $A$ +\end_inset + +. + Si la suma de sus multiplicidades da +\begin_inset Formula $n$ +\end_inset + +, resolvemos cada ecuación +\begin_inset Formula $(\lambda Id-f)X=0$ +\end_inset + + para obtener las bases de los subespacios propios, cuya dimensión debería + coincidir con la multiplicidad del autovalor si +\begin_inset Formula $A$ +\end_inset + + es diagonalizable. + Entonces añadimos cada raíz en +\begin_inset Formula $D$ +\end_inset + + tantas veces como sea su multiplicidad y razonamos que los vectores correspondi +entes de la base +\begin_inset Formula ${\cal B}$ +\end_inset + +, y por tanto las correspondientes columnas de +\begin_inset Formula $M_{{\cal CB}}$ +\end_inset + +, son los de la base de dicho subespacio propio. +\end_layout + +\begin_layout Section +Aplicaciones +\end_layout + +\begin_layout Standard +\begin_inset Formula $(x_{n})_{n}\subseteq K$ +\end_inset + + verifica una +\series bold +ecuación en diferencias lineales con coeficientes constantes +\series default + (homogénea) si para todo +\begin_inset Formula $n$ +\end_inset + + satisface que +\begin_inset Formula $x_{n+r}+a_{1}x_{n+r-1}+\dots+a_{r}x_{n}=0$ +\end_inset + +. + Llamamos a +\begin_inset Formula $r$ +\end_inset + + el +\series bold +orden +\series default + de la ecuación. + Podemos definir entonces una sucesión auxiliar +\begin_inset Formula $(Y_{n})_{n}\subseteq M_{r,1}(K)$ +\end_inset + + con +\begin_inset Formula $(Y_{n})_{i}=x_{n+r-i}$ +\end_inset + +. + Se tiene entonces que +\begin_inset Formula $x_{n+r}=-a_{1}x_{n+r-1}-\dots-a_{r}x_{n}$ +\end_inset + +, luego +\begin_inset Formula +\[ +\begin{array}{c} +Y_{n+1}=\left(\begin{array}{c} +x_{n+r}\\ +\vdots\\ +x_{n+1} +\end{array}\right)=\left(\begin{array}{c} +-a_{1}x_{n+r-1}-\dots-a_{r}x_{n}\\ +x_{n+r-1}\\ +\vdots\\ +x_{n+1} +\end{array}\right)=\\ +=\left(\begin{array}{cccc} +-a_{1} & -a_{2} & \cdots & -a_{r}\\ +1 & & 0 & 0\\ + & \ddots & & \vdots\\ +0 & & 1 & 0 +\end{array}\right)\left(\begin{array}{c} +x_{n+r-1}\\ +\vdots\\ +x_{n} +\end{array}\right)=AY_{n} +\end{array} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Un +\series bold +sistema de ecuaciones en diferencias lineales de primer orden con coeficientes + constantes +\series default + (homogéneo) es una relación entre los términos de unas sucesiones y sus + términos inmediatamente anteriores: +\begin_inset Formula +\[ +\left.\begin{array}{ccc} +x_{n+1} & = & a_{11}x_{n}+a_{12}y_{n}+a_{13}z_{n}\\ +y_{n+1} & = & a_{21}x_{n}+a_{22}y_{n}+a_{23}z_{n}\\ +z_{n+1} & = & a_{31}x_{n}+a_{32}y_{n}+a_{33}z_{n} +\end{array}\right\} +\] + +\end_inset + +Estos pueden expresarme matricialmente de la forma +\begin_inset Formula $Y_{n+1}=AY_{n}$ +\end_inset + + con +\begin_inset Formula $A=(a_{ij})$ +\end_inset + +. + Por re +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +cu +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +rren +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +- +\end_layout + +\end_inset + +cia, en ambos casos se tiene que +\begin_inset Formula $Y_{n}=A^{n-1}Y_{1}=A^{n}Y_{0}$ +\end_inset + +. + Entonces es útil diagonalizar +\begin_inset Formula $A$ +\end_inset + +, si es posible, para poder calcular las potencias rápidamente. +\end_layout + +\end_body +\end_document |
