4

Here is my attempt:

\[
E_{ij} =
\begin{blockarray}{ccccccc}
 &  & \text{$j$-th column} &  &  \\
 &  & \downarrow &  &  \\
\begin{block}{(ccccc)cc}
    &   &   \vdots& \\
    &   &   0& \\
 \cdots &0  &   1& 0 & \cdots &\leftarrow&\text{$i$-th row}\\
    &   &   0& \\
    &   &   \vdots& \\
\end{block}
\end{blockarray}
\]

enter image description here I see two problems:

  1. the text "j-th column" makes the column too wide.

  2. The $E_ij$ is not centered relative to the parenthesis.

How can I solve these problems?

2 Answers 2

1

The hard way. ;-)

\documentclass{article}
\usepackage{amsmath}
\usepackage{xparse}

\NewDocumentCommand{\canonicalmatrix}{mO{th}mO{th}}{%
  \begin{array}{@{}c@{}}
  \vphantom{
    \begin{array}{@{}c@{}}\text{$#3$-#4 column}\\\downarrow\end{array}
  }
  \\
  \hphantom{E_{#1#3}={}\enspace}
  \begin{pmatrix}
  & & \smash[t]{
        \begin{array}[b]{@{}c@{}}
        \makebox[0pt]{$#3$-#4 column}\\
        \downarrow\\[-.5ex]
        \vdots
        \end{array}
      }
  \\
  & & 0
  \\
  \llap{$E_{#1#3}={}$\quad}
  \cdots & 0 & 1 & 0 & \cdots\rlap{\quad$\leftarrow$ $#1$-#2 row}
  \\
  & & 0
  \\
  & & \vdots
  \end{pmatrix}
  \end{array}%\hphantom{\text{\enspace$\leftarrow$ $#1$-#2 row}}
}

\begin{document}

\[
\canonicalmatrix{i}{j}
\]
\[
\canonicalmatrix{2}[nd]{3}[rd]
\]

\end{document}

enter image description here

5

Here it is using a TABstack.

\documentclass{article}
\usepackage{tabstackengine,amsmath}
\stackMath
\def\Vdots{\smash{\protect\raisebox{-1.5pt}{$\vdots$}}}
\begin{document}
\[
\setstacktabbedgap{1.5ex}
E_{ij} =
\stackon{\parenMatrixstack{
    &   &   \Vdots& &\\
    &   &   0& \\
 \cdots & 0  & 1& 0 & \cdots\\
    &   &   0& \\
    &   &   \Vdots& 
}}{\stackunder{\text{$j$-th column}}{\downarrow}}\leftarrow\text{$i$-th row}
\]
\end{document}

enter image description here

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