\documentclass[10pt,a4paper]{article} % Packages \usepackage{fancyhdr} % For header and footer \usepackage{multicol} % Allows multicols in tables \usepackage{tabularx} % Intelligent column widths \usepackage{tabulary} % Used in header and footer \usepackage{hhline} % Border under tables \usepackage{graphicx} % For images \usepackage{xcolor} % For hex colours %\usepackage[utf8x]{inputenc} % For unicode character support \usepackage[T1]{fontenc} % Without this we get weird character replacements \usepackage{colortbl} % For coloured tables \usepackage{setspace} % For line height \usepackage{lastpage} % Needed for total page number \usepackage{seqsplit} % Splits long words. %\usepackage{opensans} % Can't make this work so far. Shame. Would be lovely. \usepackage[normalem]{ulem} % For underlining links % Most of the following are not required for the majority % of cheat sheets but are needed for some symbol support. \usepackage{amsmath} % Symbols \usepackage{MnSymbol} % Symbols \usepackage{wasysym} % Symbols %\usepackage[english,german,french,spanish,italian]{babel} % Languages % Document Info \author{Trina Dey} \pdfinfo{ /Title (matrices.pdf) /Creator (Cheatography) /Author (Trina Dey) /Subject (Matrices Cheat Sheet) } % Lengths and widths \addtolength{\textwidth}{6cm} \addtolength{\textheight}{-1cm} \addtolength{\hoffset}{-3cm} \addtolength{\voffset}{-2cm} \setlength{\tabcolsep}{0.2cm} % Space between columns \setlength{\headsep}{-12pt} % Reduce space between header and content \setlength{\headheight}{85pt} % If less, LaTeX automatically increases it \renewcommand{\footrulewidth}{0pt} % Remove footer line \renewcommand{\headrulewidth}{0pt} % Remove header line \renewcommand{\seqinsert}{\ifmmode\allowbreak\else\-\fi} % Hyphens in seqsplit % This two commands together give roughly % the right line height in the tables \renewcommand{\arraystretch}{1.3} \onehalfspacing % Commands \newcommand{\SetRowColor}[1]{\noalign{\gdef\RowColorName{#1}}\rowcolor{\RowColorName}} % Shortcut for row colour \newcommand{\mymulticolumn}[3]{\multicolumn{#1}{>{\columncolor{\RowColorName}}#2}{#3}} % For coloured multi-cols \newcolumntype{x}[1]{>{\raggedright}p{#1}} % New column types for ragged-right paragraph columns \newcommand{\tn}{\tabularnewline} % Required as custom column type in use % Font and Colours \definecolor{HeadBackground}{HTML}{333333} \definecolor{FootBackground}{HTML}{666666} \definecolor{TextColor}{HTML}{333333} \definecolor{DarkBackground}{HTML}{B97A95} \definecolor{LightBackground}{HTML}{FAF6F8} \renewcommand{\familydefault}{\sfdefault} \color{TextColor} % Header and Footer \pagestyle{fancy} \fancyhead{} % Set header to blank \fancyfoot{} % Set footer to blank \fancyhead[L]{ \noindent \begin{multicols}{3} \begin{tabulary}{5.8cm}{C} \SetRowColor{DarkBackground} \vspace{-7pt} {\parbox{\dimexpr\textwidth-2\fboxsep\relax}{\noindent \hspace*{-6pt}\includegraphics[width=5.8cm]{/web/www.cheatography.com/public/images/cheatography_logo.pdf}} } \end{tabulary} \columnbreak \begin{tabulary}{11cm}{L} \vspace{-2pt}\large{\bf{\textcolor{DarkBackground}{\textrm{Matrices Cheat Sheet}}}} \\ \normalsize{by \textcolor{DarkBackground}{Trina Dey} via \textcolor{DarkBackground}{\uline{cheatography.com/136953/cs/28643/}}} \end{tabulary} \end{multicols}} \fancyfoot[L]{ \footnotesize \noindent \begin{multicols}{3} \begin{tabulary}{5.8cm}{LL} \SetRowColor{FootBackground} \mymulticolumn{2}{p{5.377cm}}{\bf\textcolor{white}{Cheatographer}} \\ \vspace{-2pt}Trina Dey \\ \uline{cheatography.com/trina-dey} \\ \end{tabulary} \vfill \columnbreak \begin{tabulary}{5.8cm}{L} \SetRowColor{FootBackground} \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Cheat Sheet}} \\ \vspace{-2pt}Published 3rd September, 2021.\\ Updated 3rd September, 2021.\\ Page {\thepage} of \pageref{LastPage}. \end{tabulary} \vfill \columnbreak \begin{tabulary}{5.8cm}{L} \SetRowColor{FootBackground} \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Sponsor}} \\ \SetRowColor{white} \vspace{-5pt} %\includegraphics[width=48px,height=48px]{dave.jpeg} Measure your website readability!\\ www.readability-score.com \end{tabulary} \end{multicols}} \begin{document} \raggedright \raggedcolumns % Set font size to small. Switch to any value % from this page to resize cheat sheet text: % www.emerson.emory.edu/services/latex/latex_169.html \footnotesize % Small font. \begin{multicols*}{3} \begin{tabularx}{5.377cm}{x{1.69218 cm} x{3.28482 cm} } \SetRowColor{DarkBackground} \mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{Matrices}} \tn % Row 0 \SetRowColor{LightBackground} Addition & X + Y = {[}zij{]} = {[}xij + yij{]} \tn % Row Count 2 (+ 2) % Row 1 \SetRowColor{white} Subtraction & X - Y = {[}zij{]} = {[}xij - yij{]} \tn % Row Count 4 (+ 2) % Row 2 \SetRowColor{LightBackground} \seqsplit{Multiplication} & X * Y = {[}zij{]} = {[} xi * yj{]} \tn % Row Count 6 (+ 2) % Row 3 \SetRowColor{white} Constant & c * X = {[}zij{]} = {[}c * xij{]} \tn % Row Count 7 (+ 1) \hhline{>{\arrayrulecolor{DarkBackground}}--} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{x{2.58804 cm} x{2.38896 cm} } \SetRowColor{DarkBackground} \mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{Transpose \& Identity}} \tn % Row 0 \SetRowColor{LightBackground} Transpose & X\textasciicircum{}T\textasciicircum{} = {[}zij{]} = {[}xji{]} \tn % Row Count 2 (+ 2) % Row 1 \SetRowColor{white} Tr of Tr & (X\textasciicircum{}T\textasciicircum{})\textasciicircum{}T\textasciicircum{} = X \tn % Row Count 3 (+ 1) % Row 2 \SetRowColor{LightBackground} Tr of Mul & (XY)\textasciicircum{}T\textasciicircum{} = Y\textasciicircum{}T\textasciicircum{} {\emph{ X\textasciicircum{}T\textasciicircum{} != X\textasciicircum{}T\textasciicircum{} }} Y\textasciicircum{}T\textasciicircum{} \tn % Row Count 5 (+ 2) % Row 3 \SetRowColor{white} Sym Matrix & X\textasciicircum{}T\textasciicircum{} = X \tn % Row Count 6 (+ 1) % Row 4 \SetRowColor{LightBackground} Identity Matrix I \{\{nl\}\} {[}zii=1, zij=0{]} & X {\emph{ I = I }} X = X \tn % Row Count 8 (+ 2) \hhline{>{\arrayrulecolor{DarkBackground}}--} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{x{1.09494 cm} x{3.88206 cm} } \SetRowColor{DarkBackground} \mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{Inverse}} \tn % Row 0 \SetRowColor{LightBackground} Inverse & X X\textasciicircum{}-1\textasciicircum{} = I = X\textasciicircum{}-1\textasciicircum{}X \tn % Row Count 1 (+ 1) % Row 1 \SetRowColor{white} \mymulticolumn{2}{x{5.377cm}}{if X\textasciicircum{}-1\textasciicircum{} exists then X is non singular or invertible} \tn % Row Count 3 (+ 2) % Row 2 \SetRowColor{LightBackground} Inv of Inv & (X\textasciicircum{}-1\textasciicircum{})\textasciicircum{}-1\textasciicircum{} = X \tn % Row Count 5 (+ 2) % Row 3 \SetRowColor{white} Inv of Mul & (XY)\textasciicircum{}-1\textasciicircum{} = Y\textasciicircum{}-1\textasciicircum{}X\textasciicircum{}-1\textasciicircum{} != X\textasciicircum{}-1\textasciicircum{}Y\textasciicircum{}-1\textasciicircum{} \tn % Row Count 7 (+ 2) % Row 4 \SetRowColor{LightBackground} Inv of Tr & (X\textasciicircum{}T\textasciicircum{})\textasciicircum{}-1\textasciicircum{} = (X\textasciicircum{}-1\textasciicircum{})\textasciicircum{}T\textasciicircum{} \tn % Row Count 9 (+ 2) % Row 5 \SetRowColor{white} \seqsplit{Determinant} & |A| = \textasciicircum{}n\textasciicircum{}∑`i=1` a`i``j` x Det |a`i``j`| \tn % Row Count 11 (+ 2) % Row 6 \SetRowColor{LightBackground} \mymulticolumn{2}{x{5.377cm}}{Determinant is computed over first row of matrix where each element of first row is multiplied by its minor} \tn % Row Count 14 (+ 3) % Row 7 \SetRowColor{white} \mymulticolumn{2}{x{5.377cm}}{minor M`i``j` is a determinant obtained by deleting the i\textasciicircum{}th\textasciicircum{} row and j\textasciicircum{}th\textasciicircum{} column in which a`i``j` lies. Minor of a`i``j` is denoted by m`i``j`.} \tn % Row Count 17 (+ 3) % Row 8 \SetRowColor{LightBackground} \seqsplit{Cofactor} & A`i``j` = (-1)\textasciicircum{}i+j\textasciicircum{} m`i``j` \tn % Row Count 18 (+ 1) % Row 9 \SetRowColor{white} Adjoint & adj(A) = (Cofactor)\textasciicircum{}T\textasciicircum{} = (A`i``j`)\textasciicircum{}T\textasciicircum{} \tn % Row Count 20 (+ 2) % Row 10 \SetRowColor{LightBackground} Inverse & A\textasciicircum{}-1\textasciicircum{} = adj(A) / |A| \tn % Row Count 21 (+ 1) \hhline{>{\arrayrulecolor{DarkBackground}}--} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{X} \SetRowColor{DarkBackground} \mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Orthogonal}} \tn % Row 0 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{Two n x 1 vectors are orthogonal if X\textasciicircum{}T\textasciicircum{} Y = 0} \tn % Row Count 1 (+ 1) % Row 1 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{A vector is orthonormal if X\textasciicircum{}T\textasciicircum{}X = ||X\textasciicircum{}2\textasciicircum{}||} \tn % Row Count 2 (+ 1) % Row 2 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{Sq root of ||X|| is length or norm of vector} \tn % Row Count 3 (+ 1) % Row 3 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{\{X`1`, X`2`, X`3`.... X`n`) are said to be orthonormal if, each pair is orthogonal and have unit length} \tn % Row Count 6 (+ 3) % Row 4 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{A sq matrix is orthogonal if X\textasciicircum{}T\textasciicircum{}X= I or X\textasciicircum{}T\textasciicircum{}=X\textasciicircum{}-1\textasciicircum{}} \tn % Row Count 8 (+ 2) \hhline{>{\arrayrulecolor{DarkBackground}}-} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{X} \SetRowColor{DarkBackground} \mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Eigen Values \& Eigen Vectors}} \tn % Row 0 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{A is nxn matrix, X is nx1 matrix, λ is a scalar, then} \tn % Row Count 2 (+ 2) % Row 1 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{AX = λX or (A-λI)X = 0 or X = (A-λI)\textasciicircum{}-1\textasciicircum{}} \tn % Row Count 3 (+ 1) % Row 2 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{λ is the eigen value and X is the eigen vector (non zero)} \tn % Row Count 5 (+ 2) % Row 3 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{Since X is non zero, |A-λI| should be 0} \tn % Row Count 6 (+ 1) % Row 4 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{Determinant for {[}a b{]} = ad - bc \{\{nl\}\}~~~~~~~~~~~~~~~~~~~~~~~~~{[}c d{]}} \tn % Row Count 10 (+ 4) % Row 5 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{If A =\textgreater{} symmetric, then eigenvalues =\textgreater{} real \& \{\{nl\}\} eigenvectors =\textgreater{} orthogonal} \tn % Row Count 12 (+ 2) % Row 6 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{Diagonalization: P =\textgreater{} orthogonal matrix, then Z = P\textasciicircum{}T\textasciicircum{}AP, Z is diagonal matrix with eigen values of A} \tn % Row Count 15 (+ 3) \hhline{>{\arrayrulecolor{DarkBackground}}-} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{X} \SetRowColor{DarkBackground} \mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Linear Independence}} \tn % Row 0 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{Given a`1`x`1` + a`2`x`2` + ...a`n`x`n` = 0, if a vector {[}a`1`, a`2`, ...a`n`{]} exists such that} \tn % Row Count 2 (+ 2) % Row 1 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{a. all a`i` are 0, then x`i` are linearly independent.} \tn % Row Count 4 (+ 2) % Row 2 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{b. if some a`i`!=0 then x`i` are linearly dependent.} \tn % Row Count 6 (+ 2) % Row 3 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{If a set of vectors are linearly dependent, then one of them can be written as some combination of others} \tn % Row Count 9 (+ 3) % Row 4 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{A set of two vectors is linearly dependent if and only if one of the vectors is a constant multiple of the other.} \tn % Row Count 12 (+ 3) \hhline{>{\arrayrulecolor{DarkBackground}}-} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{X} \SetRowColor{DarkBackground} \mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Idempotence}} \tn % Row 0 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{a nxn matrix A is idempotent iff A\textasciicircum{}2\textasciicircum{} = A} \tn % Row Count 1 (+ 1) % Row 1 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{The identity matrix I is idempotent.} \tn % Row Count 2 (+ 1) % Row 2 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{Let X be an n×k matrix of full rank ,n≥k then H exists as H=X(X\textasciicircum{}T\textasciicircum{}X)\textasciicircum{}−1\textasciicircum{}X\textasciicircum{}T\textasciicircum{} and is idempotent.} \tn % Row Count 4 (+ 2) \hhline{>{\arrayrulecolor{DarkBackground}}-} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{X} \SetRowColor{DarkBackground} \mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{ColBreak2}} \tn % Row 0 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{} \tn % Row Count 0 (+ 0) \hhline{>{\arrayrulecolor{DarkBackground}}-} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{X} \SetRowColor{DarkBackground} \mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Rank}} \tn % Row 0 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{For a nxk matrix say X, the column vectors are {[}x`1`, x`2`, ...x`k`{]} and {\bf{{\emph{rank}}}} is given by max num of linearly independent vectors.} \tn % Row Count 3 (+ 3) % Row 1 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{If X is a nxk matrix and r(X) = k, then X is of full rank for n≥k.} \tn % Row Count 5 (+ 2) % Row 2 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{r(X) = r(X\textasciicircum{}T\textasciicircum{}) = r(X\textasciicircum{}T\textasciicircum{}X)} \tn % Row Count 6 (+ 1) % Row 3 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{If X is kxk, then X is non singular iff r(X) = k.} \tn % Row Count 7 (+ 1) % Row 4 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{If X is n×k, P is n×n and non-singular, and Q is k×k and nonsingular, then r(X) =r(PX) =r(XQ).} \tn % Row Count 9 (+ 2) % Row 5 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{The rank of a diagonal matrix is equal to the number of non zero diagonal entries in the matrix.} \tn % Row Count 11 (+ 2) % Row 6 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{r(XY) ≤ r(X) r(Y)} \tn % Row Count 12 (+ 1) \hhline{>{\arrayrulecolor{DarkBackground}}-} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{X} \SetRowColor{DarkBackground} \mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Trace}} \tn % Row 0 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{The trace of a square k×k matrix X is sum of its diagonal entries - \{\{nl\}\} tr(X) = ∑ xii} \tn % Row Count 2 (+ 2) % Row 1 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{If c is a scalar, tr(cX) =c * tr(X)} \tn % Row Count 3 (+ 1) % Row 2 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{tr(X±Y) =tr(X) ± tr(Y).} \tn % Row Count 4 (+ 1) % Row 3 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{If XY and YX both exist, tr(XY) =tr(YX).} \tn % Row Count 5 (+ 1) \hhline{>{\arrayrulecolor{DarkBackground}}-} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{X} \SetRowColor{DarkBackground} \mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Quadratic Forms}} \tn % Row 0 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{A be a k × k, y be k × 1 vector containing variables q = y\textasciicircum{}T\textasciicircum{} Ay is called a quadratic form in y, A is called the matrix of the quadratic form} \tn % Row Count 3 (+ 3) % Row 1 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{q = ∑ ∑ a`ij`y`i`y`j`} \tn % Row Count 4 (+ 1) % Row 2 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{If y\textasciicircum{}T\textasciicircum{}Ay \textgreater{} 0 for all y != 0, y\textasciicircum{}T\textasciicircum{}Ay \& A are +ve definite} \tn % Row Count 6 (+ 2) % Row 3 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{If y\textasciicircum{}T\textasciicircum{}Ay \textgreater{}= 0 for all y != 0, y\textasciicircum{}T\textasciicircum{}Ay \& A are +ve semidefinite} \tn % Row Count 8 (+ 2) \hhline{>{\arrayrulecolor{DarkBackground}}-} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{X} \SetRowColor{DarkBackground} \mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Matrix Differentiation}} \tn % Row 0 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{y = (y1, y2, . . . , yk)\textasciicircum{}T\textasciicircum{}, z = f(y) then ∂z/∂y = {[}∂z/∂y`1` ∂z/∂y`2` ∂z/∂y`3`{]}\textasciicircum{}T\textasciicircum{}} \tn % Row Count 2 (+ 2) % Row 1 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{z=a\textasciicircum{}T\textasciicircum{}y, ∂z/∂y = a} \tn % Row Count 3 (+ 1) % Row 2 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{z=y\textasciicircum{}T\textasciicircum{}y, ∂z/∂y = 2y} \tn % Row Count 4 (+ 1) % Row 3 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{z=y\textasciicircum{}T\textasciicircum{}Ay, ∂z/∂y = Ay+A\textasciicircum{}T\textasciicircum{}y , if A is symmetrix then ∂z/∂y = 2Ay} \tn % Row Count 6 (+ 2) \hhline{>{\arrayrulecolor{DarkBackground}}-} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{X} \SetRowColor{DarkBackground} \mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Page Break1}} \tn % Row 0 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{} \tn % Row Count 0 (+ 0) \hhline{>{\arrayrulecolor{DarkBackground}}-} \end{tabularx} \par\addvspace{1.3em} \begin{tabularx}{5.377cm}{X} \SetRowColor{DarkBackground} \mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Theorems}} \tn % Row 0 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{Theorem 1\{\{nl\}\} Let A be a symmetric k×k matrix. Then an orthogonal matrix P exists such that P\textasciicircum{}T\textasciicircum{}AP = λ x I, where λ = {[}λ`1`, λ`2`, .... λ`n` {]} are the eigen values of A as nx1 vector} \tn % Row Count 4 (+ 4) % Row 1 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{Theorem 2\{\{nl\}\} The eigenvalues of idempotent matrices are always either 0 or 1.} \tn % Row Count 6 (+ 2) % Row 2 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{Theorem 3\{\{nl\}\} If A is a symmetric and idempotent matrix, r(A) =tr(A)} \tn % Row Count 8 (+ 2) % Row 3 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{Theorem 4\{\{nl\}\} Let A`1`,A`2`,...,A`m` be a collection of symmetric k×k matrices. Then the following are equivalent: \{\{nl\}\}a. There exists an orthogonal matrix P such that P\textasciicircum{}T\textasciicircum{}A`i`P is diagonal for all i= 1,2,...,m; \{\{nl\}\} b. A`i`A`j`=A`j`A`i` for every pair i,j= 1,2,...,m.} \tn % Row Count 14 (+ 6) % Row 4 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{Theorem 5\{\{nl\}\} Let A`1`,A`2`,...,A`m` be a collection of symmetric k×k matrices. Then any two of the following conditions implies the third: \{\{nl\}\} a. All Ai, i= 1,2,...,m are idempotent; \{\{nl\}\} b. ∑ Ai is idempotent; \{\{nl\}\} c. AiAj= 0for i6=j} \tn % Row Count 19 (+ 5) % Row 5 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{Theorem 6 \{\{nl\}\} Let A`1`,A`2`,...,A`m` be a collection of symmetric k×k matrices. If the conditions in Theorem 5 are true, then \{\{nl\}\} r(∑A`i`) = ∑r(A`i`)} \tn % Row Count 23 (+ 4) % Row 6 \SetRowColor{LightBackground} \mymulticolumn{1}{x{5.377cm}}{Theroem 7 \{\{nl\}\} A symmetric matrix A is positive definite if and only if its eigen values are all (strictly) positive} \tn % Row Count 26 (+ 3) % Row 7 \SetRowColor{white} \mymulticolumn{1}{x{5.377cm}}{Theorem 8 \{\{nl\}\} A symmetric matrix A is positive semi-definite if and only if its eigenvalues are all non-negative.} \tn % Row Count 29 (+ 3) \hhline{>{\arrayrulecolor{DarkBackground}}-} \end{tabularx} \par\addvspace{1.3em} % That's all folks \end{multicols*} \end{document}