I am looking to produce a matrix multiplication where one of the matrices consists of coloured blocks. Much like: 
Is there any way to produce something like this in Latex?
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3 Answers
I did this with stacks. Unfortunately, there is some tailoring that one must do, depending on the arrangement of boxes, so each particular image must be thought through. The \colblock[color]{rows}{content} is the basic unit. \belowbaseline[length]{} is used in \colblock to align boxes at their top. That and \belowbaseline[length]{} can be used in the code to shift/align boxes. Passing either of them a multiple of \baselineskip would allow some staggering in the vertical box placement.
If the \colblocks are allowed to be rectangular (I assumed square), let me know so that I may correct the answer.
\documentclass{article} \usepackage{stackengine} \usepackage{xcolor} \usepackage{calc} \newlength\mytemp \newlength\myoffset \myoffset=.5\ht\strutbox \newcommand\colblock[3][blue!20]{% \setlength\mytemp{#2\baselineskip}% \setlength\mytemp{.5\mytemp-\myoffset}% \belowbaseline[0pt]{% \fboxsep=-\fboxrule\fbox{\colorbox{#1}{\rule[-\mytemp]{0ex}{#2\baselineskip}% \makebox[#2\baselineskip]{$#3$}}}% }} \begin{document} \[ \parenVectorstack{b_1 b_2 . . . . . b_n} = \left( \raisebox{4\baselineskip+.5\myoffset}{% \def\stackalignment{l}\stackunder[0pt]{\colblock{2}{-2}\colblock{2}{-2}}% {\colblock{6}{-1}\colblock[red!15]{4}{1}}% }% \right) \parenVectorstack{a_1 a_2 . . . . . a_n} \] \end{document} 
answered Feb 21, 2014 at 14:05
Steven B. Segletes
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A solution that uses tikz, but hides it in markup:
\begin{blockmatrix} \block[blue](0,0)text(2,2) \end{blockmatrix} Draws a block with color blue at position (0,0) with size (2,2) and "text" in the middle. Thus different colors and rectangles are supported.
\documentclass{article} \usepackage{amsmath} \usepackage{xcolor} \usepackage{tikz} \usetikzlibrary{calc} \definecolor{block}{RGB}{0,162,232} \newenvironment{blockmatrix}{% \left(% \vcenter\bgroup\hbox\bgroup \tikzpicture[ x=1.5\baselineskip, y=1.5\baselineskip, ]% }{% \endtikzpicture \egroup \egroup \right)% } % \block[#1](#2,#3)#4(#5,#6) % #1: fill color % (#2,#3): lower left corner % #4: text in the middle % (#5,#6): size of the block \newcommand*{\block}[1][block]{% \blockaux{#1}% } \def\blockaux#1(#2,#3)#4(#5,#6){% \draw[fill={#1}] let \p1=(#2,#3), \p2=(#5,#6), \p3=(#2+#5,#3+#6), \p4=(#2+#5/2,#3+#6/2) in (\p1) rectangle (\p3) (\p4) node {$#4$} ;% } \begin{document} \[ \begin{pmatrix}b_1\\b_2\\\vdots\\b_n\end{pmatrix} = \begin{blockmatrix} \block(0,0)-1(3,3) \block(3,1)1(2,2) \block[yellow](0,3)-2(1,1) \block[green](1,3)2(1,1) \end{blockmatrix} \begin{pmatrix}a_1\\a2\\\vdots\\a_n\end{pmatrix} \] \end{document} 
With {pNiceMatrix} of nicematrix.
\documentclass{article} \usepackage{nicematrix} \begin{document} $ \renewcommand{\arraystretch}{1.6} \begin{pmatrix} b_1 \\ b_2 \\ \vdots \\ b_n \end{pmatrix} = \begin{pNiceMatrix}[margin,columns-width=auto] \Block[fill=red!15,draw]{1-1}{-2} & \Block[fill=green!20,draw]{1-1}{2} & & & \\ \Block[fill=blue!15,draw]{3-3}{-1} & & & \Block[fill=blue!15,draw]{2-2}{1} & \\ & & & & \\ & & & & \\ \end{pNiceMatrix} \begin{pmatrix} a_1 \\ a_2 \\ \vdots \\ a_n \end{pmatrix} $ \end{document} You need several compilations (because nicematrix uses PGF/Tikz nodes under the hood).
