Matrices inside a matrix, with only text in the inner matrices

Question

I want to draw a big matrix as an 8 by 8 to represent the combination of two HMMs. How do I go about it?

First, see https://tex.stackexchange.com/questions/59517/label-rows-of-a-matrix-by-characters . I would use tikzmarks and insert the "submatrixes" using tikz (see https://tex.stackexchange.com/questions/291843/highlight-matrix-cell-and-have-arrows-pointing-from-cell-with-text for example). — John Kormylo, Sep 16 '23 at 01:05
You should look into the nicematrix package, which is exactly designed for these kinds of things. — Willie Wong, Sep 16 '23 at 03:15

score 5 · Answer 1 · answered Sep 16 '23 at 05:34

Because you didn't specify what TeX format you want to use, I show you, what to do in plainTeX. There are macros \bordermatrix, \pmatrix and \multispan. The rest are almost TeX primitives.

$$
   \def\mf #1 #2/#3 {\multispan4\kern#1pt\vtop to0pt{\null\vskip-.8\baselineskip 
       \hbox{$\displaystyle \pmatrix{\cr\hbox to5.5em{\hss#2\hss}\cr
                                 \rm\hfil#3\cr\cr}$}\vss}}
   \delcode`(=\delcode`[  \delcode`)=\delcode`]
   \bordermatrix{ &s_1&s_2&s_3&s_4&s_5&s_6&s_7&s_8\cr
              s_1 & \mf0 HMM/Data & 0 & 0 & 0 & 0  \cr
              s_1 &   &   &   &   & 0 & 0 & 0 & 0  \cr
              s_1 &   &   &   &   & 0 & 0 & 0 & 0  \cr
              s_1 &   &   &   &   & 0 & 0 & 0 & 0  \cr
              s_1 & 0 & 0 & 0 & 0 & \mf7 HMM/Noise \cr
              s_1 & 0 & 0 & 0 & 0 \cr
              s_1 & 0 & 0 & 0 & 0 \cr
              s_1 & 0 & 0 & 0 & 0 \cr
   }
$$
\bye

score 5 · Accepted Answer · answered Sep 16 '23 at 07:41

With {bNiceMatrix} of nicematrix.

\documentclass{article}
\usepackage{nicematrix}
\begin{document}
$\begin{bNiceMatrix}%
 [
  margin ,
  first-row , code-for-first-row = s_{\arabic{jCol}} , 
  first-col , code-for-first-col = s_{\arabic{iRow}} 
 ]
&&&&&&&& \
& \Block{4-4}{\text{HMM}{\text{Deta}}} 
  &&&  &0&0&0&0\
& &&&  &0&0&0&0\
& &&&  &0&0&0&0\
& &&&  &0&0&0&0\
&   0&0&0&0 & \Block{4-4}{\text{HMM}{\text{Noise}}} \
&   0&0&0&0 \
&   0&0&0&0 \
&   0&0&0&0 \
\CodeAfter
  \SubMatrix[{1-1}{4-4}][extra-height=-1mm]
  \SubMatrix[{5-5}{8-8}][extra-height=-1mm]
\end{bNiceMatrix}$
\end{document}

You need several compilations (because nicematrix uses PGF/TikZ nodes under the hood.

Matrices inside a matrix, with only text in the inner matrices

2 Answers2