[Tex/LaTex] Formatting a Block Matrix

matrices

I'm trying to typeset the matrix depicted in the diagram, I've considered many examples, and in particular easybmat. But nothing came closer than the approach I settled on given below. However it does not quite produce the accuracy I wanted. Is there a way to make the diagram closer to the required picture?

\documentclass{article}
\usepackage{amsmath}
\usepackage{multirow}
\usepackage{easybmat}

\newcommand\bigzero{\makebox(0,0){\text{\Huge0}}}
\begin{document} 

\[
\sbox0{$\begin{array}{c c c |}0&1&0\\0&0&1\\0&0&0\\ \hline\end{array}$}
\sbox1{$\begin{array}{| r|}\hline \\ 2\\ \hline\end{array}$}
\sbox2{$\begin{matrix}2&1&0\\0&2&1\\0&0&2\end{matrix}$}
\sbox3{$\begin{array}{c c c |}2&1&0\\0&2&1\\0&0&2\\ \hline\end{array}$}
%
A=\left[
\begin{array}{c c c c}
\usebox{0}&  & \bigzero & \\
& \usebox{1} &  & \\
\bigzero & & \usebox{3} & \\
& &  & 0 \\
\end{array}
\right]
\]

\end{document}

Required Picture
Gotten so far

Best Answer

For questions like this a matrix of math nodes is your friend. These are tikz matrix that allow you to draw lines connecting the matrix entries.

Here the output I get:

enter image description here

and here is the code:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{matrix}
\begin{document}

\[ A =
  \begin{tikzpicture}[baseline=(current bounding box.center),
                      large/.style={font=\large}]
    \matrix (M)[matrix of math nodes, nodes in empty cells,
                left delimiter={[}, right delimiter={]},
                column sep={1.2em,between origins},
                row sep={1.2em,between origins}
    ]{ 0 & 1 & 0 &   &              \\
       0 & 0 & 1 &   &   &   &   &  \\
       0 & 0 & 0 &   &   &          \\
         &   &   & 2 &   &          \\
         &   &   &   & 2 & 1 & 0 &  \\
         &   &   &   & 0 & 2 & 1 &  \\
         &   &   &   & 0 & 0 & 2 &  \\
         &   &   &   &   &   &   & 0\\
     };
    \draw(M-3-1.south west)--([xshift=2mm]M-3-4.south east);
    \draw(M-4-3.south)--(M-4-4.south east);
    \draw(M-7-5.south)--([xshift=2mm]M-7-7.south);
    \draw(M-1-3.north east)--(M-4-4.south west);
    \draw(M-4-4.north east)--(M-5-5.south west);
    \draw(M-5-7.north east)--(M-7-7.south east);
    \node[large] at (M-2-7){$0$};
    \node[large] at (M-7-2){$0$};
  \end{tikzpicture}
\]

\end{document}

Some words of explanation:

  • The (M) after \matrix means that the nodes have labels (M-1-1), (M-1-2) etc. You can change (M) to anything you like.
  • The node (M-3-1.south west) is the south west corner of the entry in row 3 and column 1. Simiarly, there are north, east, south, ...
  • I have used a matrix of math nodes but there is also a matrix of nodes. The difference, as you'd suspect, is that matrix of math nodes puts the matrix entries into math-mode.
  • the nodes in empty cells creates labels for empty cells.
  • I didn't put the large 0s into the matrix because this would have warped the row and column sizes
  • The lines column sep={1.2em,between origins} and row sep={1.2em,between origins} makes the distances between the center of the rows and columns the same, which you want if you are drawing vertical and horizontal lines between the matrix entries
  • you need to put braces around the delimiters in left delimiter={[} and right delimiter={]}
  • the baseline=(current bounding box.center) is there to center the matrix in the displayed equation
  • the large/.style={font=\large} sets the font size for the "large" zeros in the matrix (this is the meaning of the large in \node[large]).
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