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| author | Juan Marín Noguera <juan.marinn@um.es> | 2020-02-24 11:22:00 +0100 |
|---|---|---|
| committer | Juan Marín Noguera <juan.marinn@um.es> | 2020-02-24 11:22:00 +0100 |
| commit | 79e1a51eb55d0df43323c0fe77a7d55b2c2bd17d (patch) | |
| tree | 89bd93a329f9deb72efce8fed205b69918c3d9b9 /fvv1/n1.lyx | |
| parent | 1f7f9bcc7660fba0827a62c3068d5c7082f025d7 (diff) | |
POO
Diffstat (limited to 'fvv1/n1.lyx')
| -rw-r--r-- | fvv1/n1.lyx | 1914 |
1 files changed, 1914 insertions, 0 deletions
diff --git a/fvv1/n1.lyx b/fvv1/n1.lyx new file mode 100644 index 0000000..41aa455 --- /dev/null +++ b/fvv1/n1.lyx @@ -0,0 +1,1914 @@ +#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 french +\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 +Sea +\begin_inset Formula $E$ +\end_inset + + un +\begin_inset Formula $\mathbb{R}$ +\end_inset + +-espacio vectorial, una +\series bold +norma +\series default + es una aplicación +\begin_inset Formula $\Vert\cdot\Vert:E\rightarrow\mathbb{R}$ +\end_inset + + tal que +\begin_inset Formula $\forall x,y\in E,\lambda\in\mathbb{R}$ +\end_inset + +: +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\Vert x\Vert\geq0\land(\Vert x\Vert=0\iff x=0)$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\Vert x+y\Vert\leq\Vert x\Vert+\Vert y\Vert$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\Vert\lambda x\Vert=|\lambda|\Vert x\Vert$ +\end_inset + +. +\end_layout + +\begin_layout Standard +El par +\begin_inset Formula $(E,\Vert\cdot\Vert)$ +\end_inset + + es un +\series bold +espacio normado +\series default +. + Llamamos +\series bold +distancia asociada a la norma +\series default + a +\begin_inset Formula $d(x,y):=\Vert x-y\Vert$ +\end_inset + +. + Dos normas son equivalentes si sus distancias lo son. +\end_layout + +\begin_layout Standard +Ejemplos de normas en +\begin_inset Formula $\mathbb{R}^{n}$ +\end_inset + + son las dadas por +\begin_inset Formula $\Vert(x_{1},\dots,x_{n})\Vert_{p}:=\sqrt[p]{\sum_{i=1}^{n}|x_{i}|^{p}}$ +\end_inset + + y +\begin_inset Newline newline +\end_inset + + +\begin_inset Formula $\Vert(x_{1},\dots,x_{n})\Vert_{\infty}:=\max\{|x_{i}|\}_{i=1}^{n}$ +\end_inset + +. + Además, +\begin_inset Formula $V:={\cal C}[a,b]:=\{f:[a,b]\rightarrow\mathbb{R}\text{ continua}\}$ +\end_inset + + con +\begin_inset Formula $\Vert f\Vert_{\infty}:=\sup\{|f(x)|\}_{x\in[a,b]}$ +\end_inset + + es un espacio normado. +\end_layout + +\begin_layout Standard +\begin_inset Note Comment +status open + +\begin_layout Enumerate +Dado +\begin_inset Formula $f\in V$ +\end_inset + +, existe al menos un +\begin_inset Formula $x\in[a,b]$ +\end_inset + + y entonces +\begin_inset Formula $\Vert f\Vert_{\infty}\geq|f(x)|\geq0$ +\end_inset + +, y +\begin_inset Formula $\Vert f\Vert_{\infty}=0\iff\forall x\in[a,b],f(x)=0\iff f=0$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\Vert f+g\Vert_{\infty}=\sup\{|f(x)+g(x)|\}_{x\in[a,b]}\leq\sup\{|f(x)|+|g(x)|\}_{x\in[a,b]}\leq\sup\{|f(x)|\}_{x\in[a,b]}+\sup\{|g(x)|\}_{x\in[a,b]}=\Vert f\Vert_{\infty}+\Vert g\Vert_{\infty}$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Dado +\begin_inset Formula $\lambda\in\mathbb{R}$ +\end_inset + +, +\begin_inset Formula $\Vert\lambda f\Vert_{\infty}=\sup\{|\lambda f(x)|\}_{x\in[a,b]}=|\lambda|\sup\{|f(x)|\}_{x\in[a,b]}=|\lambda|\Vert f\Vert_{\infty}$ +\end_inset + +. +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +sremember{TEM} +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +\begin_inset Formula $f:(X,d)\rightarrow(Y,d')$ +\end_inset + + es continua en +\begin_inset Formula $p$ +\end_inset + + [...] si y sólo si +\begin_inset Formula $\forall\varepsilon>0,\exists\delta>0:\forall x\in X,(d(x,p)<\delta\implies d'(f(x),f(p))<\varepsilon)$ +\end_inset + +. +\end_layout + +\begin_layout Standard +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +eremember +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +Definimos la norma de una aplicación +\begin_inset Formula $L:(E,\Vert\cdot\Vert)\rightarrow(F,\Vert\cdot\Vert')$ +\end_inset + + como +\begin_inset Formula $\Vert L\Vert:=\Vert L\Vert_{\Vert\cdot\Vert}^{\Vert\cdot\Vert'}:=\sup\{\Vert L(x)\Vert'\}_{x\in E,\Vert x\Vert\leq1}$ +\end_inset + +, y tenemos como +\series bold +teorema +\series default + que +\begin_inset Formula $L$ +\end_inset + + es continua si y sólo si +\begin_inset Formula $\Vert L\Vert<+\infty$ +\end_inset + +, y entonces es uniformemente continua. +\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 $L$ +\end_inset + + continua en 0, es decir, +\begin_inset Formula $\forall\varepsilon>0,\exists\delta>0:\forall y\in E,(\Vert y\Vert<\delta\implies\Vert L(y)\Vert'<\varepsilon)$ +\end_inset + +. + Fijado +\begin_inset Formula $\varepsilon$ +\end_inset + +, sea +\begin_inset Formula $\Vert z\Vert\leq1$ +\end_inset + +, entonces +\begin_inset Formula $\Vert\frac{\delta}{2}z\Vert<\delta$ +\end_inset + + y +\begin_inset Formula $\Vert L(\frac{\delta}{2}z)\Vert'<\varepsilon$ +\end_inset + +, luego +\begin_inset Formula $\Vert L(z)\Vert'<\frac{2\varepsilon}{\delta}$ +\end_inset + + y +\begin_inset Formula $\Vert L\Vert<\frac{2\varepsilon}{\delta}$ +\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 + +Veamos primero que +\begin_inset Formula $\Vert L\Vert<+\infty\implies\forall x\in E,\Vert L(x)\Vert'\leq\Vert L\Vert\Vert x\Vert$ +\end_inset + +. + En efecto, para +\begin_inset Formula $\Vert x\Vert=1$ +\end_inset + +, +\begin_inset Formula $\Vert L(x)\Vert'\leq\sup\{\Vert L(y)\Vert\}_{\Vert y\Vert\leq1}=\Vert L\Vert=\Vert L\Vert\Vert x\Vert$ +\end_inset + +, y para cualquier otra +\begin_inset Formula $x$ +\end_inset + + basta dividir entre la norma. + Ahora bien, dado +\begin_inset Formula $\varepsilon>0$ +\end_inset + +, tomando +\begin_inset Formula $\delta:=\frac{\varepsilon}{\Vert L\Vert+1}$ +\end_inset + + entonces +\begin_inset Formula $\Vert y-x\Vert<\delta\implies\Vert L(y)-L(x)\Vert'=\Vert L(y-x)\Vert'\leq\Vert L\Vert\Vert y-x\Vert<\Vert L\Vert\delta=\frac{\Vert L\Vert\varepsilon}{\Vert L\Vert+1}<\varepsilon$ +\end_inset + +. + Pero como +\begin_inset Formula $\delta$ +\end_inset + + no depende de +\begin_inset Formula $x$ +\end_inset + +, +\begin_inset Formula $L$ +\end_inset + + es uniformemente continua. +\end_layout + +\begin_layout Section +Equivalencia de normas +\end_layout + +\begin_layout Standard +Dos normas +\begin_inset Formula $\Vert\cdot\Vert$ +\end_inset + + y +\begin_inset Formula $\Vert\cdot\Vert'$ +\end_inset + + son equivalentes si y sólo si +\begin_inset Formula $\exists\alpha,\beta>0:\forall x\in E,\alpha\Vert x\Vert\leq\Vert x\Vert'\leq\beta\Vert x\Vert$ +\end_inset + +. + +\series bold +Demostración: +\series default + Sean +\begin_inset Formula $L:=id_{E}:(E,\Vert\cdot\Vert)\rightarrow(E,\Vert\cdot\Vert')$ +\end_inset + + y +\begin_inset Formula $L':=L^{-1}$ +\end_inset + +, entonces +\begin_inset Formula ${\cal T}_{\Vert\cdot\Vert}={\cal T}_{\Vert\cdot\Vert'}$ +\end_inset + + si y sólo si +\begin_inset Formula $L$ +\end_inset + + y +\begin_inset Formula $L'$ +\end_inset + + son continuas, pues +\begin_inset Formula $L\text{ es continua}\iff\forall A\in{\cal T}_{\Vert\cdot\Vert'},A\in{\cal T}_{\Vert\cdot\Vert}\iff{\cal T}_{\Vert\cdot\Vert'}\subseteq{\cal T}_{\Vert\cdot\Vert}$ +\end_inset + +, y el otro contenido es análogo. + Entonces: +\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 $L$ +\end_inset + + es continua +\begin_inset Formula $\Vert L\Vert<+\infty$ +\end_inset + +, luego +\begin_inset Formula $\Vert x\Vert'=\Vert L(x)\Vert'\leq\Vert L\Vert\Vert x\Vert\overset{\beta:=\Vert L\Vert}{=}\beta\Vert x\Vert$ +\end_inset + +. + La otra cota se hace de forma análoga. +\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 existe +\begin_inset Formula $\beta$ +\end_inset + + tal que +\begin_inset Formula $\forall x\in E,\Vert x\Vert'\leq\beta\Vert x\Vert$ +\end_inset + +, en particular se cumple para +\begin_inset Formula $\Vert x\Vert\leq1$ +\end_inset + +, y entonces +\begin_inset Formula $\Vert L(x)\Vert=\Vert x\Vert'\leq\beta\Vert x\Vert$ +\end_inset + +, luego +\begin_inset Formula $\Vert L\Vert=\sup\{\Vert x\Vert'\}_{\Vert x\Vert\leq1}\leq\beta<+\infty$ +\end_inset + + y +\begin_inset Formula $L$ +\end_inset + + es continua. +\end_layout + +\begin_layout Standard +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +sremember{TEM} +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +Las métricas +\begin_inset Formula $d_{E}$ +\end_inset + +, +\begin_inset Formula $d_{T}$ +\end_inset + + y +\begin_inset Formula $d_{\infty}$ +\end_inset + + [...] son equivalentes, [...]. + +\series bold +Demostración: +\series default + Se deduce de que +\begin_inset Formula $\frac{1}{n}d_{T}(x,y)\leq d_{\infty}(x,y)\leq d_{T}(x,y)$ +\end_inset + + y +\begin_inset Formula $\frac{1}{\sqrt{n}}d_{E}(x,y)\leq d_{\infty}(x,y)\leq d_{E}(x,y)$ +\end_inset + +. + [...] +\end_layout + +\begin_layout Standard +Todo cerrado +\begin_inset Formula $C$ +\end_inset + + de un compacto +\begin_inset Formula $(X,{\cal T})$ +\end_inset + + es compacto. + [...] En [...] +\begin_inset Formula $(\mathbb{R},{\cal T}_{u})$ +\end_inset + + [...] todo subespacio cerrado y acotado es compacto. + [...] Todo subespacio compacto +\begin_inset Formula $K$ +\end_inset + + de un espacio métrico +\begin_inset Formula $(X,d)$ +\end_inset + + es [cerrado y] acotado. + [...]Si +\begin_inset Formula $f:(X,{\cal T})\rightarrow(Y,{\cal T}')$ +\end_inset + + es continua y +\begin_inset Formula $(X,{\cal T})$ +\end_inset + + es compacto entonces +\begin_inset Formula $f(X)$ +\end_inset + + es compacto. + [...] +\begin_inset Formula $(X,{\cal T})$ +\end_inset + + es +\series bold +compacto +\series default +[...] si toda sucesión admite una subsucesión convergente. +\end_layout + +\begin_layout Standard +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +eremember +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +Toda norma +\begin_inset Formula $\Vert\cdot\Vert:(E,\Vert\cdot\Vert)\rightarrow\mathbb{R}$ +\end_inset + + es uniformemente continua. + +\series bold +Demostración: +\series default + Fijado +\begin_inset Formula $\varepsilon$ +\end_inset + + y tomando +\begin_inset Formula $\delta:=\varepsilon$ +\end_inset + +, si +\begin_inset Formula $\Vert x-y\Vert<\delta$ +\end_inset + + entonces usando que +\begin_inset Formula $|\Vert x\Vert-\Vert y\Vert|\leq\Vert x-y\Vert$ +\end_inset + +, lo que se deduce de +\begin_inset Formula $\Vert x\Vert\leq\Vert x-y\Vert+\Vert y\Vert$ +\end_inset + + y +\begin_inset Formula $\Vert y\Vert\leq\Vert y-x\Vert+\Vert x\Vert$ +\end_inset + +, obtenemos que +\begin_inset Formula $|\Vert x\Vert-\Vert y\Vert|<\varepsilon$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Como +\series bold +teorema +\series default +, en +\begin_inset Formula $\mathbb{R}^{n}$ +\end_inset + +, todas las normas son equivalentes. +\end_layout + +\begin_layout Labeling +\labelwidthstring 00.00.0000 +\begin_inset Formula $\Vert x\Vert\leq C\Vert x\Vert_{1}]$ +\end_inset + + +\begin_inset Formula $\Vert x\Vert=\Vert\sum x_{i}\vec{e}_{i}\Vert\leq\sum|x_{i}|\Vert\vec{e}_{i}\Vert\leq\max\{\Vert\vec{e}_{i}\Vert\}\sum|x_{i}|=\max\{\Vert\vec{e}_{i}\Vert\}\Vert x\Vert_{1}$ +\end_inset + +. +\end_layout + +\begin_layout Labeling +\labelwidthstring 00.00.0000 +\begin_inset Formula $\Vert x\Vert_{1}\leq D\Vert x\Vert]$ +\end_inset + + Tomamos +\begin_inset Formula $(\mathbb{R}^{n},\Vert\cdot\Vert_{1})\overset{id}{\rightarrow}(\mathbb{R}^{n},\Vert\cdot\Vert)\overset{\Vert\cdot\Vert}{\rightarrow}\mathbb{R}$ +\end_inset + +, que es continua por ser composición de dos funciones continuas (la identidad + es continua por la otra cota y la demostración del teorema anterior), entonces + +\begin_inset Formula $S:=\{x\in\mathbb{R}^{n}:\Vert x\Vert_{1}=1\}$ +\end_inset + + es cerrado dentro del compacto +\begin_inset Formula $\overline{B}(0,1)$ +\end_inset + +, luego es compacto y como la función dada es continua, +\begin_inset Formula $\Vert\cdot\Vert(S)$ +\end_inset + + es compacto y alcanza su máximo y su mínimo. + Sea ahora +\begin_inset Formula $\mu:=\min\{\Vert x\Vert\}_{x\in S}>0$ +\end_inset + + (pues +\begin_inset Formula $0\notin S$ +\end_inset + +), si +\begin_inset Formula $\Vert x\Vert_{1}=1$ +\end_inset + + para un cierto +\begin_inset Formula $x\in\mathbb{R}^{n}$ +\end_inset + +, entonces +\begin_inset Formula $\Vert x\Vert\geq\mu$ +\end_inset + +, luego +\begin_inset Formula $x\neq0$ +\end_inset + + y +\begin_inset Formula $\left\Vert \frac{x}{\Vert x\Vert_{1}}\right\Vert =1$ +\end_inset + +, con lo que +\begin_inset Formula $\left\Vert \frac{x}{\Vert x\Vert_{1}}\right\Vert \geq\mu$ +\end_inset + + y +\begin_inset Formula $\Vert x\Vert\geq\mu\Vert x\Vert_{1}$ +\end_inset + +, y entonces +\begin_inset Formula $\Vert x\Vert_{1}\leq\frac{1}{\mu}\Vert x\Vert$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Tenemos pues que toda +\begin_inset Formula $T:(\mathbb{R}^{m},\Vert\cdot\Vert)\rightarrow(\mathbb{R}^{n},\Vert\cdot\Vert')$ +\end_inset + + lineal es continua +\begin_inset Note Comment +status open + +\begin_layout Plain Layout +, pues equivale a una multiplicación por una matriz en +\begin_inset Formula $M_{n\times m}(\mathbb{R})$ +\end_inset + +, que es continua con la norma euclídea y por tanto en todas las demás +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Section +Convergencia +\end_layout + +\begin_layout Standard +Sea +\begin_inset Formula $(X,{\cal T})$ +\end_inset + + un espacio topológico e +\begin_inset Formula $(Y,d)$ +\end_inset + + un espacio métrico, una sucesión de funciones +\begin_inset Formula $(f_{n}:(X,{\cal T})\rightarrow(Y,d))_{n}$ +\end_inset + + +\series bold +converge puntualmente +\series default + a +\begin_inset Formula $f:(X,{\cal T})\rightarrow(Y,d)$ +\end_inset + + si para todo +\begin_inset Formula $x\in X$ +\end_inset + +, +\begin_inset Formula $f_{n}(x)\rightarrow f(x)$ +\end_inset + +, y converge +\series bold +uniformemente +\series default + a +\begin_inset Formula $f$ +\end_inset + + si +\begin_inset Formula $d_{\infty}(f_{n},f)\rightarrow0$ +\end_inset + +. + Sea +\begin_inset Formula $x_{0}\in(X,{\cal T})$ +\end_inset + + y +\begin_inset Formula $(f_{n}:X\rightarrow\mathbb{R})_{n}$ +\end_inset + + una sucesión de funciones continuas en +\begin_inset Formula $x_{0}$ +\end_inset + + que converge uniformemente a +\begin_inset Formula $f$ +\end_inset + +, entonces +\begin_inset Formula $f$ +\end_inset + + es continua en +\begin_inset Formula $x_{0}$ +\end_inset + +. + +\series bold +Demostración: +\series default + Fijado un +\begin_inset Formula $\varepsilon>0$ +\end_inset + +, existe un +\begin_inset Formula $n_{0}\in\mathbb{N}$ +\end_inset + + tal que para +\begin_inset Formula $n\geq n_{0}$ +\end_inset + + y +\begin_inset Formula $x\in X$ +\end_inset + + se tiene +\begin_inset Formula $|f_{n}(x)-f(x)|<\frac{\varepsilon}{3}$ +\end_inset + +. + Como +\begin_inset Formula $f_{n}$ +\end_inset + + es continua, existe +\begin_inset Formula ${\cal V}\in{\cal E}(x_{0})$ +\end_inset + + tal que si +\begin_inset Formula $x\in{\cal V}$ +\end_inset + + entonces +\begin_inset Formula $|f_{n}(x)-f_{n}(x_{0})|<\frac{\varepsilon}{3}$ +\end_inset + +, con lo que +\begin_inset Formula $|f(x)-f(x_{0})|\leq|f(x)-f_{n}(x)|+|f_{n}(x)-f_{n}(x_{0})|+|f_{n}(x_{0})-f(x_{0})|<\frac{\varepsilon}{3}+\frac{\varepsilon}{3}+\frac{\varepsilon}{3}=\varepsilon$ +\end_inset + +. +\end_layout + +\begin_layout Standard +\begin_inset Note Comment +status open + +\begin_layout Plain Layout +El límite puntual de funciones continuas no es necesariamente continua, + ni siquera en funciones de +\begin_inset Formula $(a,b)$ +\end_inset + + a +\begin_inset Formula $\mathbb{R}$ +\end_inset + +, y como contraejemplo tenemos +\begin_inset Formula $(f_{n}:(-1,1)\rightarrow\mathbb{R})_{n}$ +\end_inset + + dada por +\begin_inset Formula $f_{n}(x)=\begin{cases} +0 & \text{si }x\leq0\\ +nx & \text{si }0<x<\frac{1}{n}\\ +1 & \text{si }x\geq\frac{1}{n} +\end{cases}$ +\end_inset + +, que converge a +\begin_inset Formula $f(x)=\begin{cases} +0 & \text{si }x\leq0\\ +1 & \text{si }x>0 +\end{cases}$ +\end_inset + +. + Asimismo, el límite uniforme de funciones derivables no es necesariamente + derivable, y como contraejemplo tenemos +\begin_inset Formula $f_{n}(x)=\sqrt{x^{2}+\frac{1}{n}}$ +\end_inset + +, que converge a +\begin_inset Formula $f(x)=|x|$ +\end_inset + +. +\end_layout + +\begin_layout Plain Layout +La función +\begin_inset Formula $\sum_{n}\frac{\cos(7^{n}\pi x)}{2^{n}}$ +\end_inset + + es continua en todos los puntos ( +\begin_inset Formula $\Vert\frac{\cos(7^{n}\pi x)}{2^{n}}\Vert_{\infty}=\frac{1}{2^{n}}\implies\Vert\sum_{n}\frac{\cos(7^{n}\pi x)}{2^{n}}\Vert<+\infty$ +\end_inset + +, con lo que la función es continua por ser la suma de una sucesión convergente + de funciones continuas) pero no es derivable en ninguno. +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +sremember{FUVR1} +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $\lim_{n}x_{n}=\pm\infty$ +\end_inset + + entonces +\begin_inset Formula $\lim_{n}\left(1+\frac{1}{x_{n}}\right)^{x_{n}}=e$ +\end_inset + + y +\begin_inset Formula $\lim_{n}\left(1-\frac{1}{x_{n}}\right)^{x_{n}}=e^{-1}$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +Si existe +\begin_inset Formula $\lim_{n}\frac{z_{n+1}}{z_{n}}=w\in\mathbb{R}$ +\end_inset + + con +\begin_inset Formula $|w|<1$ +\end_inset + +, entonces +\begin_inset Formula $\lim_{n}z_{n}=0$ +\end_inset + +. + [...] +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $b>0$ +\end_inset + +, +\begin_inset Formula $c>1$ +\end_inset + + y +\begin_inset Formula $d>0$ +\end_inset + +, entonces +\begin_inset Formula +\[ +\log n\ll n^{b}\ll c^{n}\ll n^{dn} +\] + +\end_inset + +Si además +\begin_inset Formula $d\geq1$ +\end_inset + +, entonces +\begin_inset Formula $c^{n}\ll n!\ll n^{dn}$ +\end_inset + +. + [...] +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $\lim_{n}x_{n}=0$ +\end_inset + + con +\begin_inset Formula $0<|x_{n}|<1$ +\end_inset + +, entonces: +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $\log(1+x_{n})\sim x_{n}$ +\end_inset + +. +\end_layout + +\begin_layout Enumerate +\begin_inset Formula $e^{x_{n}}-1\sim x_{n}$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $\lim_{n}x_{n}=1$ +\end_inset + + con +\begin_inset Formula $x_{n}\neq1$ +\end_inset + + y +\begin_inset Formula $\lim_{n}y_{n}=\pm\infty$ +\end_inset + +, entonces +\begin_inset Formula +\[ +\lim_{n}x_{n}^{y_{n}}=e^{\lim_{n}y_{n}(x_{n}-1)} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Si +\begin_inset Formula $\lim_{n}x_{n}=0$ +\end_inset + + y +\begin_inset Formula $x_{n}\neq0$ +\end_inset + +, entonces +\begin_inset Formula $\sin x_{n}\sim x_{n}$ +\end_inset + +. +\end_layout + +\begin_layout Standard + +\series bold +Criterios de Stolz: +\series default + Si +\begin_inset Formula $(a_{n})_{n}$ +\end_inset + + y +\begin_inset Formula $(b_{n})_{n}$ +\end_inset + + son sucesiones de reales tales que +\begin_inset Formula $(b_{n})_{n}$ +\end_inset + + es estrictamente creciente o decreciente y bien +\begin_inset Formula $\lim_{n}a_{n}=\lim_{n}b_{n}=0$ +\end_inset + +, bien +\begin_inset Formula $\lim_{n}b_{n}=\infty$ +\end_inset + +, si existe +\begin_inset Formula $\lim_{n}\frac{a_{n+1}-a_{n}}{b_{n+1}-b_{n}}=L\in\overline{\mathbb{R}}$ +\end_inset + +, entonces +\begin_inset Formula $\lim_{n}\frac{a_{n}}{b_{n}}=L$ +\end_inset + +. +\end_layout + +\begin_layout Standard +Como consecuencia: +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $(a_{n})_{n}$ +\end_inset + + converge, entonces +\begin_inset Formula +\[ +\lim_{n}\frac{a_{1}+\dots+a_{n}}{n}=\lim_{n}a_{n} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $(a_{n})_{n}$ +\end_inset + + converge y +\begin_inset Formula $a_{n}>0$ +\end_inset + +, entonces +\begin_inset Formula +\[ +\lim_{n}\sqrt[n]{a_{1}\cdots a_{n}}=\lim_{n}a_{n} +\] + +\end_inset + + +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $a_{n}>0$ +\end_inset + + y existe +\begin_inset Formula $\lim_{n}\frac{a_{n}}{a_{n-1}}$ +\end_inset + +, entonces +\begin_inset Formula +\[ +\lim_{n}\sqrt[n]{a_{n}}=\lim_{n}\frac{a_{n}}{a_{n-1}} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +eremember +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +sremember{FUVR1} +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +La +\series bold +condición de Cauchy +\series default + nos dice que +\begin_inset Formula $\sum_{n}a_{n}$ +\end_inset + + es convergente si y sólo si +\begin_inset Formula $\forall\varepsilon>0,\exists n_{0}\in\mathbb{N}:\forall p,q\in\mathbb{N},(n_{0}\leq p\leq q\implies|a_{p+1}+\dots+a_{q}|<\varepsilon)$ +\end_inset + +. +\end_layout + +\begin_layout Standard +[...] Si +\begin_inset Formula $S_{n}$ +\end_inset + + converge, entonces +\begin_inset Formula $\lim_{n}a_{n}=0$ +\end_inset + +. + [...] La convergencia de una serie no se altera modificando un número finito + de términos de esta. + [...] +\end_layout + +\begin_layout Standard +Dada una serie +\begin_inset Formula $\sum_{n=1}^{\infty}a_{n}$ +\end_inset + + de términos +\begin_inset Formula $a_{n}\geq0$ +\end_inset + +, esta es convergente si y sólo si la sucesión de sumas parciales es acotada + [...]. +\end_layout + +\begin_layout Standard + +\series bold +Criterios de comparación: +\end_layout + +\begin_layout Enumerate +Dadas +\begin_inset Formula $\sum_{n}a_{n}$ +\end_inset + + y +\begin_inset Formula $\sum_{n}b_{n}$ +\end_inset + + con +\begin_inset Formula $a_{n},b_{n}\geq0$ +\end_inset + +, si existe +\begin_inset Formula $M>0$ +\end_inset + + tal que +\begin_inset Formula $a_{n}\leq Mb_{n}\forall n$ +\end_inset + +, entonces la convergencia de +\begin_inset Formula $\sum_{n=1}^{\infty}b_{n}$ +\end_inset + + implica la de +\begin_inset Formula $\sum_{n=1}^{\infty}a_{n}$ +\end_inset + + [...]. +\end_layout + +\begin_layout Enumerate +Dadas +\begin_inset Formula $\sum_{n}a_{n}$ +\end_inset + + y +\begin_inset Formula $\sum_{n}b_{n}$ +\end_inset + + con +\begin_inset Formula $a_{n},b_{n}>0$ +\end_inset + + y existe +\begin_inset Formula $l:=\lim_{n}\frac{a_{n}}{b_{n}}\in\mathbb{R}\cup\{+\infty\}$ +\end_inset + +: +\end_layout + +\begin_deeper +\begin_layout Enumerate +Si +\begin_inset Formula $0<l<\infty$ +\end_inset + +, ambas series tienen el mismo carácter. + [...] +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $l=0$ +\end_inset + + entonces la convergencia de +\begin_inset Formula $\sum_{n}b_{n}$ +\end_inset + + implica la de +\begin_inset Formula $\sum_{n}a_{n}$ +\end_inset + +. + [...] +\end_layout + +\begin_layout Enumerate +Si +\begin_inset Formula $l=+\infty$ +\end_inset + + entonces la convergencia de +\begin_inset Formula $\sum_{n}a_{n}$ +\end_inset + + implica la de +\begin_inset Formula $\sum_{n}b_{n}$ +\end_inset + +. + [...] +\end_layout + +\end_deeper +\begin_layout Standard + +\series bold +Criterio de la raíz: +\series default + Dada +\begin_inset Formula $\sum_{n}a_{n}$ +\end_inset + + con +\begin_inset Formula $a_{n}>0$ +\end_inset + + y +\begin_inset Formula $a:=\lim_{n}\sqrt[n]{a_{n}}\in\mathbb{R}$ +\end_inset + +: +\end_layout + +\begin_layout Itemize +Si +\begin_inset Formula $a<1$ +\end_inset + +, la serie converge. + [...] +\end_layout + +\begin_layout Itemize +Si +\begin_inset Formula $a>1$ +\end_inset + +, la serie diverge. + [...] +\end_layout + +\begin_layout Itemize +Si +\begin_inset Formula $a=1$ +\end_inset + + no se puede afirmar nada. +\end_layout + +\begin_layout Standard + +\series bold +Criterio del cociente: +\series default + Sea +\begin_inset Formula $\sum_{n}a_{n}$ +\end_inset + + con +\begin_inset Formula $a_{n}>0$ +\end_inset + + y +\begin_inset Formula $a:=\lim_{n}\frac{a_{n+1}}{a_{n}}\in\mathbb{R}$ +\end_inset + +. + [...] +\end_layout + +\begin_layout Itemize +Si +\begin_inset Formula $a<1$ +\end_inset + +, la serie converge. +\end_layout + +\begin_layout Itemize +Si +\begin_inset Formula $a>1$ +\end_inset + +, la serie diverge. +\end_layout + +\begin_layout Standard + +\series bold +Criterio de condensación: +\series default + Dada una sucesión +\begin_inset Formula $(a_{n})_{n}$ +\end_inset + + monótona decreciente con +\begin_inset Formula $a_{n}>0$ +\end_inset + +. + Entonces +\begin_inset Formula +\[ +\sum_{n=1}^{\infty}a_{n}\in\mathbb{R}\iff\sum_{n=1}^{\infty}2^{n}a_{2^{n}}\in\mathbb{R} +\] + +\end_inset + + +\end_layout + +\begin_layout Standard +Una serie +\begin_inset Formula $\sum_{n}a_{n}$ +\end_inset + + con +\begin_inset Formula $a_{n}\in\mathbb{R}$ +\end_inset + + es +\series bold +absolutamente convergente +\series default + si +\begin_inset Formula $\sum_{n}|a_{n}|$ +\end_inset + + es convergente. + Toda serie absolutamente convergente es convergente. + [...] +\end_layout + +\begin_layout Standard +La +\series bold +serie geométrica +\series default + +\begin_inset Formula $\sum_{n=0}^{\infty}r^{n}$ +\end_inset + + es convergente si +\begin_inset Formula $|r|<1$ +\end_inset + + con suma +\begin_inset Formula $\frac{1}{1-r}$ +\end_inset + + y divergente si +\begin_inset Formula $|r|\geq1$ +\end_inset + +. + La +\series bold +serie armónica +\series default + +\begin_inset Formula $\sum_{n=1}^{\infty}\frac{1}{n^{k}}$ +\end_inset + + es convergente si +\begin_inset Formula $k>1$ +\end_inset + + y divergente si +\begin_inset Formula $k\leq1$ +\end_inset + +. +\end_layout + +\begin_layout Standard +\begin_inset ERT +status open + +\begin_layout Plain Layout + + +\backslash +eremember +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Section +Completitud +\end_layout + +\begin_layout Standard +Una sucesión +\begin_inset Formula $(x_{n})$ +\end_inset + + en un espacio métrico +\begin_inset Formula $(E,d)$ +\end_inset + + es +\series bold +de Cauchy +\series default + si +\begin_inset Formula $\forall\varepsilon>0,\exists n_{\varepsilon}\in\mathbb{N}:\forall n,m\geq n_{\varepsilon},d(x_{n},x_{m})<\varepsilon$ +\end_inset + +. + Un espacio métrico es +\series bold +completo +\series default + si toda sucesión de Cauchy es convergente. + Un +\series bold +espacio de Banach +\series default + es un espacio normado completo. + Dadas dos normas +\begin_inset Formula $\Vert\cdot\Vert$ +\end_inset + + y +\begin_inset Formula $\Vert\cdot\Vert'$ +\end_inset + + equivalentes sobre +\begin_inset Formula $E$ +\end_inset + +, +\begin_inset Formula $(E,\Vert\cdot\Vert)$ +\end_inset + + es completo si y sólo si lo es +\begin_inset Formula $(E,\Vert\cdot\Vert')$ +\end_inset + +. +\begin_inset Note Comment +status open + +\begin_layout Plain Layout + +\series bold +Demostración: +\series default + Existen +\begin_inset Formula $\alpha,\beta>0$ +\end_inset + + tales que +\begin_inset Formula $\alpha\Vert x\Vert\leq\Vert x\Vert'\leq\beta\Vert x\Vert$ +\end_inset + +, luego si +\begin_inset Formula $(x_{n})$ +\end_inset + + es de Cauchy en +\begin_inset Formula $(E,\Vert\cdot\Vert)$ +\end_inset + + también lo es en +\begin_inset Formula $(E,\Vert\cdot\Vert')$ +\end_inset + + sin más que tomar +\begin_inset Formula $n_{\frac{\varepsilon}{\beta}}$ +\end_inset + +, y viceversa, y como +\begin_inset Formula $(x_{n})$ +\end_inset + + converge a +\begin_inset Formula $x$ +\end_inset + + en +\begin_inset Formula $(E,\Vert\cdot\Vert)$ +\end_inset + + si y sólo si converge en +\begin_inset Formula $(E,\Vert\cdot\Vert')$ +\end_inset + +, la completitud de uno implica la del otro. +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard +Como +\series bold +teorema +\series default +, +\begin_inset Formula $\mathbb{R}^{n}$ +\end_inset + + es un espacio de Banach con cualquier norma. + +\series bold +Demostración: +\series default + Basta probar que +\begin_inset Formula $(\mathbb{R}^{n},\Vert\cdot\Vert_{\infty})$ +\end_inset + + es completo. + Si +\begin_inset Formula $(x_{m})$ +\end_inset + + es de Cauchy en +\begin_inset Formula $(\mathbb{R}^{n},\Vert\cdot\Vert_{\infty})$ +\end_inset + +, como +\begin_inset Formula $|x_{mi}-x_{ki}|\leq\Vert x_{m}-x_{k}\Vert_{\infty}$ +\end_inset + + para todo +\begin_inset Formula $i\in\{1,\dots,n\}$ +\end_inset + +, entonces +\begin_inset Formula $(x_{mi})_{m}$ +\end_inset + + es de Cauchy en +\begin_inset Formula $\mathbb{R}$ +\end_inset + + y por tanto convergente a un +\begin_inset Formula $x_{0i}$ +\end_inset + +, con lo que +\begin_inset Formula $(x_{m})_{m}$ +\end_inset + + converge a +\begin_inset Formula $(x_{01},\dots,x_{0n})$ +\end_inset + +, y se tiene que +\begin_inset Formula $(\mathbb{R}^{n},\Vert\cdot\Vert)$ +\end_inset + + es completo. +\end_layout + +\begin_layout Standard +Como +\series bold +teorema +\series default +, +\begin_inset Formula $({\cal C}[a,b],\Vert\cdot\Vert_{\infty})$ +\end_inset + + es un espacio de Banach. + +\series bold +Demostración: +\series default + Sea +\begin_inset Formula $(f_{n})_{n}$ +\end_inset + + una sucesión de Cauchy en +\begin_inset Formula $({\cal C}[a,b],\Vert\cdot\Vert_{\infty})$ +\end_inset + +, fijado un +\begin_inset Formula $\varepsilon>0$ +\end_inset + + existe un +\begin_inset Formula $n_{0}$ +\end_inset + + tal que para +\begin_inset Formula $n,m\geq n_{0}$ +\end_inset + + y +\begin_inset Formula $x\in[a,b]$ +\end_inset + +, +\begin_inset Formula $|f_{n}(x)-f_{m}(x)|<\frac{\varepsilon}{2}$ +\end_inset + +. + Por tanto para cada +\begin_inset Formula $x\in[a,b]$ +\end_inset + +, +\begin_inset Formula $(f_{n}(x))_{n}$ +\end_inset + + es de Cauchy en +\begin_inset Formula $\mathbb{R}$ +\end_inset + + y converge pues a un valor +\begin_inset Formula $f(x)$ +\end_inset + +. + Ahora bien, dado un +\begin_inset Formula $x\in[a,b]$ +\end_inset + +, por la convergencia puntual que acabamos de probar existe +\begin_inset Formula $n_{x}\in\mathbb{N}$ +\end_inset + + tal que para +\begin_inset Formula $n\geq n_{x}$ +\end_inset + + se tiene +\begin_inset Formula $|f_{n}(x)-f(x)|<\frac{\varepsilon}{2}$ +\end_inset + +. + Si +\begin_inset Formula $n>n_{0}$ +\end_inset + +, +\begin_inset Formula $|f_{n}(x)-f(x)|\leq|f_{n}(x)-f_{\max\{n_{0},n_{x}\}}(x)|+|f_{\max\{n_{0},n_{x}\}}(x)-f(x)|<\frac{\varepsilon}{2}+\frac{\varepsilon}{2}=\varepsilon$ +\end_inset + +, y como +\begin_inset Formula $n_{0}$ +\end_inset + + no depende de +\begin_inset Formula $x$ +\end_inset + + (sólo de +\begin_inset Formula $\varepsilon$ +\end_inset + +), queda probada la convergencia uniforme. +\end_layout + +\begin_layout Standard +Sea +\begin_inset Formula $(x_{n})_{n}$ +\end_inset + + una sucesión en el espacio de Banach +\begin_inset Formula $(E,\Vert\cdot\Vert)$ +\end_inset + + con +\begin_inset Formula $\sum_{n}\Vert x_{n}\Vert<+\infty$ +\end_inset + +, entonces +\begin_inset Formula $\sum_{n}x_{n}$ +\end_inset + + converge. +\begin_inset Note Comment +status open + +\begin_layout Plain Layout + +\series bold +Demostración: +\series default + Tenemos que +\begin_inset Formula $\sum_{n}\Vert x_{n}\Vert$ +\end_inset + +, por ser convergente, es de Cachy, por lo que dado +\begin_inset Formula $\varepsilon>0$ +\end_inset + + existe +\begin_inset Formula $n_{\varepsilon}$ +\end_inset + + tal que si +\begin_inset Formula $n,m>n_{\varepsilon}$ +\end_inset + + se tiene +\begin_inset Formula $|\sum_{k=1}^{n}\Vert x_{k}\Vert-\sum_{k=1}^{m}\Vert x_{k}\Vert|<\varepsilon$ +\end_inset + +. + Pero por la desigualdad triangular +\begin_inset Formula $\Vert\sum_{k=1}^{n}x_{k}-\sum_{k=1}^{m}x_{k}\Vert\leq|\sum_{k=1}^{n}\Vert x_{k}\Vert-\sum_{k=1}^{m}\Vert x_{k}\Vert|<\varepsilon$ +\end_inset + +, luego +\begin_inset Formula $\sum_{n}x_{n}$ +\end_inset + + también es de Cauchy y por tanto convergente por estar en un espacio completo. +\end_layout + +\end_inset + + +\end_layout + +\end_body +\end_document |
