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| author | Juan Marín Noguera <juan@mnpi.eu> | 2025-05-16 22:18:44 +0200 |
|---|---|---|
| committer | Juan Marín Noguera <juan@mnpi.eu> | 2025-05-16 22:18:44 +0200 |
| commit | 4f670b750af5c11e1eac16d9cd8556455f89f46a (patch) | |
| tree | e0f8d7b33df2727d89150f799ee8628821fda80a /1.2.9.lyx | |
| parent | 16ccda6c459c0fd7ca2081e9d541124c28b0c556 (diff) | |
Changed layout for more manageable volumes
Diffstat (limited to '1.2.9.lyx')
| -rw-r--r-- | 1.2.9.lyx | 846 |
1 files changed, 0 insertions, 846 deletions
diff --git a/1.2.9.lyx b/1.2.9.lyx deleted file mode 100644 index 6bc6c57..0000000 --- a/1.2.9.lyx +++ /dev/null @@ -1,846 +0,0 @@ -#LyX 2.4 created this file. For more info see https://www.lyx.org/ -\lyxformat 620 -\begin_document -\begin_header -\save_transient_properties true -\origin unavailable -\textclass book -\use_default_options true -\maintain_unincluded_children no -\language american -\language_package default -\inputencoding utf8 -\fontencoding auto -\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_roman_osf false -\font_sans_osf false -\font_typewriter_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 -\float_placement class -\float_alignment class -\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_formatted_ref 0 -\use_minted 0 -\use_lineno 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 english -\dynamic_quotes 0 -\papercolumns 1 -\papersides 1 -\paperpagestyle default -\tablestyle default -\tracking_changes false -\output_changes false -\change_bars false -\postpone_fragile_content true -\html_math_output 0 -\html_css_as_file 0 -\html_be_strict false -\docbook_table_output 0 -\docbook_mathml_prefix 1 -\end_header - -\begin_body - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -rexerc2[M13] -\end_layout - -\end_inset - -Prove Eq. - (11). -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -answer -\end_layout - -\end_inset - - -\begin_inset Formula -\[ -\left(\sum_{n\geq0}\frac{a_{n}}{n!}z^{n}\right)\left(\sum_{m\geq0}\frac{b_{m}}{m!}z^{m}\right)=\sum_{n\geq0}\left(\sum_{k}\frac{a_{k}b_{n-k}}{k!(n-k)!}\right)z^{n}=\sum_{n\geq0}\frac{1}{n!}\left(\sum_{k}\binom{n}{k}a_{k}b_{n-k}\right)z^{n}. -\] - -\end_inset - - -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -exerc4[M01] -\end_layout - -\end_inset - -Explain why Eq. - (19) is a special case of Eq. - (21). -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -answer -\end_layout - -\end_inset - -Just set -\begin_inset Formula $t=0$ -\end_inset - -, - then -\begin_inset Formula $x=1+z$ -\end_inset - -. -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -rexerc6[HM15] -\end_layout - -\end_inset - -Find the generating function for -\begin_inset Formula -\[ -\left\langle \sum_{0<k<n}\frac{1}{k(n-k)}\right\rangle ; -\] - -\end_inset - -differentiate it and express the coefficients in terms of harmonic numbers. -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -answer -\end_layout - -\end_inset - -The generating function is -\begin_inset Formula -\begin{align*} -G(z) & \coloneqq\sum_{n\geq0}\sum_{0<k<n}\frac{1}{k(n-k)}z^{n}=\sum_{n,m\geq1}\frac{z^{n+m}}{nm}=\left(\sum_{n\geq1}\frac{z^{n}}{n}\right)\left(\sum_{m\geq1}\frac{z^{m}}{m}\right)=\left(\sum_{n\geq1}\frac{z^{n}}{n}\right)^{2}\\ - & =\left(-\sum_{n\geq1}\frac{(-1)^{n+1}}{n}(-z)^{n}\right)^{2}=(-\ln(1+(-z)))^{2}=\ln(1-z)^{2}, -\end{align*} - -\end_inset - -by Eq. - (24). - Its derivative is -\begin_inset Formula -\[ -\dot{G}(z)=-\frac{2}{1-z}\ln(1-z)=\frac{2}{1-z}\ln\left(\frac{1}{1-z}\right), -\] - -\end_inset - -so by Eq. - (25) with -\begin_inset Formula $m=0$ -\end_inset - - the coefficients are -\begin_inset Formula $[z^{n}]\dot{G}(z)=2(H_{n}-H_{0})\binom{n}{n}=2H_{n}$ -\end_inset - -. -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -rexerc10[M25] -\end_layout - -\end_inset - -An -\emph on -elementary symmetric function -\emph default - is defined by the formula -\begin_inset Formula -\[ -e_{m}=\sum_{1\leq j_{1}<\dots<j_{m}\leq n}x_{j_{1}}\cdots x_{j_{m}}. -\] - -\end_inset - -(This is the same as -\begin_inset Formula $h_{m}$ -\end_inset - - of Eq. - (33), - except that equal subscripts are not allowed.) Find the generating function for -\begin_inset Formula $e_{m}$ -\end_inset - -, - and express -\begin_inset Formula $e_{m}$ -\end_inset - - in terms of the -\begin_inset Formula $S_{j}$ -\end_inset - - in Eq. - (34). - Write out the formulas for -\begin_inset Formula $e_{1}$ -\end_inset - -, - -\begin_inset Formula $e_{2}$ -\end_inset - -, - -\begin_inset Formula $e_{3}$ -\end_inset - -, - and -\begin_inset Formula $e_{4}$ -\end_inset - -. -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -answer -\end_layout - -\end_inset - -Here -\begin_inset Formula $m\leq n$ -\end_inset - - or otherwise we have no elements, - so -\begin_inset Formula -\begin{align*} -G(z) & \coloneqq\sum_{m\geq0}e_{m}z^{m}=\sum_{m=0}^{n}\sum_{1\leq j_{1}<\dots<j_{k}\leq n}x_{j_{1}}\cdots x_{j_{m}}z^{n}=\sum_{a_{1},\dots,a_{n}\in\{0,1\}}\prod_{i=1}^{n}(x_{i}z)^{a_{i}}\\ - & =\prod_{i=1}^{n}\sum_{a\in\{0,1\}}(x_{i}z)^{a}=\prod_{i=1}^{n}(x_{i}z+1), -\end{align*} - -\end_inset - -as we can regard the sum as taking the product of each subset of -\begin_inset Formula $\{x_{i}z\}_{i}$ -\end_inset - -. - From here, -\begin_inset Formula -\[ -\ln G(z)=\sum_{i=1}^{n}\ln(1+x_{i}z)=\sum_{i=1}^{n}\sum_{k\geq1}\frac{(-1)^{k+1}}{k}x_{i}^{k}z^{k}=\sum_{k\geq1}\frac{(-1)^{k+1}}{k}S_{k}z^{k}, -\] - -\end_inset - -so -\begin_inset Formula -\begin{align*} -G(z) & =\text{e}^{\ln G(z)}=\exp\left(\sum_{k\geq1}\frac{(-1)^{k+1}}{k}S_{k}z^{k}\right)=\prod_{k\geq1}\text{e}^{(-1)^{k+1}S_{k}z^{k}/k}\\ - & =\prod_{k\geq1}\sum_{j\geq0}\frac{1}{j!}\left(\frac{(-1)^{k+1}S_{k}}{k}\right)^{j}z^{jk}=\sum_{m\geq0}\left(\sum_{\begin{subarray}{c} -j_{1},\dots,j_{m}\geq0\\ -j_{1}+2j_{2}+\dots+mj_{m}=m -\end{subarray}}\prod_{k=1}^{m}\frac{1}{j_{k}!}\left(\frac{(-1)^{k+1}S_{k}}{k}\right)^{j_{k}}\right)z^{m}. -\end{align*} - -\end_inset - -This gives us an explicit formulation for -\begin_inset Formula $e_{m}$ -\end_inset - -. - Note that -\begin_inset Formula -\[ -\prod_{k=1}^{m}(-1)^{(k+1)j_{k}}=(-1)^{\sum_{k=1}^{m}kj_{k}+\sum_{k=1}^{m}j_{k}}=(-1)^{m+\sum_{k}j_{k}}, -\] - -\end_inset - -so -\begin_inset Formula -\[ -e_{m}=\sum_{\begin{subarray}{c} -j_{1},\dots,j_{m}\geq0\\ -j_{1}+2j_{2}+\dots+mj_{m}=m -\end{subarray}}(-1)^{m+j_{1}+\dots+j_{m}}\prod_{k=1}^{m}\frac{S_{k}^{j_{k}}}{k^{j_{k}}j_{k}!}. -\] - -\end_inset - - -\end_layout - -\begin_layout Standard -For example, - if we call -\begin_inset Formula $p_{kj_{k}}$ -\end_inset - - to each of the factors of the product in this latest formula, - using that each -\begin_inset Formula $p_{k0}=1$ -\end_inset - - and can therefore be ignored, -\begin_inset Formula -\begin{align*} -e_{1} & =p_{11}=S_{1},\\ -e_{2} & =p_{12}+p_{21}=\frac{S_{1}^{2}}{2}-\frac{S_{2}}{2}=\frac{1}{2}(S_{1}^{2}-S_{2}),\\ -e_{3} & =p_{13}-p_{11}p_{21}+p_{31}=\frac{S_{1}^{3}}{6}-S_{1}\frac{S_{2}}{2}+\frac{S_{3}}{3}=\frac{1}{6}(S_{1}^{3}+2S_{3}-3S_{1}S_{2}),\\ -e_{4} & =p_{14}-p_{12}p_{21}+p_{11}p_{31}+p_{22}-p_{41}=\frac{S_{1}^{4}}{24}-\frac{S_{1}^{2}}{2}\frac{S_{2}}{2}+S_{1}\frac{S_{3}}{3}+\frac{S_{2}^{2}}{8}-\frac{S_{4}}{4}\\ - & =\frac{1}{24}(S_{1}^{4}-6S_{1}^{2}S_{2}+8S_{1}S_{3}+3S_{2}^{2}-6S_{4}). -\end{align*} - -\end_inset - - -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -rexerc11[M25] -\end_layout - -\end_inset - -Equation (39) can also be used to express the -\begin_inset Formula $S$ -\end_inset - -'s in terms of the -\begin_inset Formula $h$ -\end_inset - -'s: - We find -\begin_inset Formula $S_{1}=h_{1}$ -\end_inset - -, - -\begin_inset Formula $S_{2}=2h_{2}-h_{1}^{2}$ -\end_inset - -, - -\begin_inset Formula $S_{3}=3h_{3}-3h_{1}h_{2}+h_{1}^{3}$ -\end_inset - -, - etc. - What is the coefficient of -\begin_inset Formula $h_{1}^{k_{1}}h_{2}^{k_{2}}\cdots h_{m}^{k_{m}}$ -\end_inset - - in this representation of -\begin_inset Formula $S_{m}$ -\end_inset - -, - when -\begin_inset Formula $k_{1}+2k_{2}+\dots+mk_{m}=m$ -\end_inset - -? -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -answer -\end_layout - -\end_inset - - -\begin_inset Note Greyedout -status open - -\begin_layout Plain Layout -(I had to look up the solution.) -\end_layout - -\end_inset - - We ignore Eq. - (39) and focus on Eqs. - (37) and (24). - There, -\begin_inset Formula -\begin{align*} -\sum_{k\geq1}\frac{S_{k}z^{k}}{k!} & =\ln G(z)=\ln\left(1+\sum_{j\geq1}h_{j}z^{j}\right)=\sum_{k\geq1}\frac{(-1)^{k+1}}{k}\left(\sum_{j\geq1}h_{j}z^{j}\right)^{k}\\ - & =\sum_{k\geq1}\frac{(-1)^{k+1}}{k}\sum_{j_{1},\dots,j_{k}\geq1}h_{j_{1}}\cdots h_{j_{k}}z^{j_{1}+\dots+j_{k}}\\ - & =\sum_{m\geq1}\sum_{\begin{subarray}{c} -i_{1},\dots,i_{m}\geq0\\ -i_{1}+2i_{2}+\dots+mi_{m}=m -\end{subarray}}\frac{(-1)^{i_{1}+\dots+i_{m}+1}}{i_{1}+\dots+i_{m}}\binom{i_{1}+\dots+i_{m}}{i_{1},\dots,i_{m}}h_{1}^{i_{1}}\cdots h_{m}^{i_{m}}z^{m}, -\end{align*} - -\end_inset - -so the coefficient is -\begin_inset Formula -\[ -\frac{(-1)^{k_{1}+\dots+k_{m}+1}(k_{1}+\dots+k_{m})!}{k_{1}!\cdots k_{m}!}. -\] - -\end_inset - -For the last identity, - we have regrouped all the terms by the value of -\begin_inset Formula $m\coloneqq j_{1}+\dots+j_{k}$ -\end_inset - - and then by -\begin_inset Formula $\{i_{j}\coloneqq|\{t\mid j_{t}=j\}|\}_{j=1}^{m}$ -\end_inset - -, - that is, - the number of times that each -\begin_inset Formula $h_{j}$ -\end_inset - - appears rather than the indexes of those that do. - When doing this, - we note that -\begin_inset Formula $k=i_{1}+\dots+i_{m}$ -\end_inset - - and that -\begin_inset Formula $h_{j_{1}}\cdots h_{j_{k}}=h_{1}^{i_{1}}\cdots h_{m}^{i_{m}}$ -\end_inset - -, - so all the addends in a given group are the same, - and the number of addends is the number of orderings of the -\begin_inset Formula $k$ -\end_inset - - indexes without considering the order of indexes that are equal, - of which there are -\begin_inset Formula $i_{1}$ -\end_inset - - indexes equal to 1, - -\begin_inset Formula $i_{2}$ -\end_inset - - equal to 2, - etc., - and this is a multinomial coefficient. -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -rexerc12[M20] -\end_layout - -\end_inset - -Suppose we have a doubly subscripted sequence -\begin_inset Formula $\langle a_{mn}\rangle$ -\end_inset - - for -\begin_inset Formula $m,n=0,1,\dots$ -\end_inset - -; - show how this double sequence can be represented by a -\emph on -single -\emph default - generating function of two variables, - and determine the generating function for -\begin_inset Formula $\langle\binom{n}{m}\rangle$ -\end_inset - -. -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -answer -\end_layout - -\end_inset - -A generating function in this case could be something like -\begin_inset Formula -\[ -G(y,z)\coloneqq\sum_{m,n\geq0}a_{mn}y^{m}z^{n}=\sum_{n\geq0}\left(\sum_{m\geq0}a_{mn}y^{m}\right)z^{n}=\sum_{m\geq0}\left(\sum_{n\geq0}a_{mn}z^{n}\right)y^{m}. -\] - -\end_inset - -In our case, - by the binomial theorem, -\begin_inset Formula -\[ -(1+y)^{n}=\sum_{m\geq0}\binom{n}{m}y^{m}, -\] - -\end_inset - -so -\begin_inset Formula -\[ -G(y,z)=\sum_{n\geq0}(1+y)^{n}z^{n}=\frac{1}{1-(1+y)z}. -\] - -\end_inset - - -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -rexerc18[M25] -\end_layout - -\end_inset - -Given positive integers -\begin_inset Formula $n$ -\end_inset - - and -\begin_inset Formula $r$ -\end_inset - -, - find a simple formula for the value of the following sums: -\end_layout - -\begin_layout Enumerate -\begin_inset Formula $\sum_{1\leq k_{1}<k_{2}<\dots<k_{r}\leq n}k_{1}k_{2}\cdots k_{r}$ -\end_inset - -; -\end_layout - -\begin_layout Enumerate -\begin_inset Formula $\sum_{1\leq k_{1}\leq k_{2}\leq\dots\leq k_{r}\leq n}k_{1}k_{2}\cdots k_{r}$ -\end_inset - -. -\end_layout - -\begin_layout Standard -(For example, - when -\begin_inset Formula $n=3$ -\end_inset - - and -\begin_inset Formula $r=2$ -\end_inset - - the sums are, - respectively, - -\begin_inset Formula $1\cdot2+1\cdot3+2\cdot3$ -\end_inset - - and -\begin_inset Formula $1\cdot1+1\cdot2+1\cdot3+2\cdot2+2\cdot3+3\cdot3$ -\end_inset - -.) -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -answer -\end_layout - -\end_inset - - -\end_layout - -\begin_layout Enumerate -Following Exercise 10 and then applying Equation (27), -\begin_inset Formula -\begin{align*} -G(z) & \coloneqq\sum_{r\geq0}\sum_{1\leq k_{1}<\dots<k_{r}\leq n}k_{1}\cdots k_{r}=\prod_{k=1}^{n}(1+kz)=z^{n}\prod_{k=1}^{n}\left(\frac{1}{z}+k\right)\\ - & =z^{n+1}\prod_{k=0}^{n}\left(\frac{1}{z}+k\right)=z^{n+1}\sum_{k\geq0}\stirla{n+1}{k}z^{-k}\\ - & =\sum_{k=0}^{n+1}\stirla{n+1}{k}z^{n+1-k}=\sum_{k=0}^{n+1}\stirla{n+1}{n+1-k}z^{k}, -\end{align*} - -\end_inset - -so the sum is -\begin_inset Formula $\stirla{n+1}{n+1-r}$ -\end_inset - -. -\end_layout - -\begin_layout Enumerate -Doing something similar with Equations (36) and (28), -\begin_inset Formula -\begin{align*} -G(z) & \coloneqq\sum_{r\geq0}\sum_{1\leq k_{1}\leq\dots\leq k_{r}\leq n}k_{1}\cdots k_{r}=\prod_{k=1}^{n}\frac{1}{1-kz}=\frac{1}{z^{n}}\sum_{k\geq n}\stirlb{k}{n}z^{k}\\ - & =\sum_{k}\stirlb{k+n}{n}z^{k}, -\end{align*} - -\end_inset - -so the sum is -\begin_inset Formula $\stirlb{n+r}{n}$ -\end_inset - -. -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -rexerc25[M23] -\end_layout - -\end_inset - -Evaluate the sum -\begin_inset Formula $\sum_{k}\binom{n}{k}\binom{2n-2k}{n-k}(-2)^{k}$ -\end_inset - - by simplifying the equivalent formula -\begin_inset Formula $\sum_{k}[w^{k}](1-2w)^{n}[z^{n-k}](1+z)^{2n-2k}$ -\end_inset - -. -\end_layout - -\begin_layout Standard -\begin_inset ERT -status open - -\begin_layout Plain Layout - - -\backslash -answer -\end_layout - -\end_inset - -By the binomial theorem, -\begin_inset Formula -\begin{align*} -(1-2w)^{n} & =\sum_{k\geq0}\binom{n}{k}(-2)^{k}w^{k}, & (1+z)^{2n-2k} & =\sum_{j\geq0}\binom{2n-2k}{j}z^{j}, -\end{align*} - -\end_inset - -so the second formula is indeed equivalent to the first, - assuming of course that -\begin_inset Formula $n\in\mathbb{N}$ -\end_inset - - and therefore terms with negative -\begin_inset Formula $k$ -\end_inset - - or -\begin_inset Formula $k>n$ -\end_inset - - are null. - Now, - -\begin_inset Formula $[z^{n-k}](1+z)^{2n-2k}=[z^{n}](z^{k}(1+z)^{2n-2k})$ -\end_inset - -, - so this is -\begin_inset Formula -\[ -S\coloneqq[z^{n}](1+z)^{2n}\sum_{k}[w^{k}](1-2w)^{n}\left(\frac{z}{(1+z)^{2}}\right)^{k}=[z^{n}](1+z)^{2n}\left(1-\frac{2z}{(1+z)^{2}}\right)^{n}, -\] - -\end_inset - -where we evaluating the sum by taking -\begin_inset Formula $\frac{z}{(1+z)^{2}}$ -\end_inset - - as the argument of the generating function in -\begin_inset Formula $w$ -\end_inset - -. - Then, - we simplify to get -\begin_inset Formula -\[ -S=[z^{n}]\left(\left((1+z)^{2}(1-\nicefrac{2z}{(1+z)^{2}})\right)^{n}\right)=[z^{n}]\left((1+z^{2})^{n}\right)=\binom{n}{\nicefrac{n}{2}}[n\text{ even}]. -\] - -\end_inset - - -\end_layout - -\end_body -\end_document |
