Shrinking the size of a labeled matrix using a block array

Question

I have created a matrix that I would like to label. However, I would like to have the labels on the smallmatrix environment rather than using an array as I have done in order to get labels into the matrix. Below I show both the labeled matrix and the size difference relative to the smallmatrix environment.

\documentclass[12pt]{article}%
\usepackage{amsmath}
\usepackage{blkarray}

\begin{document}

\[
\begin{blockarray}{ccccccc}
      & A     & B     & C     & D     & E     & F \\
\begin{block}{c[cccccc]}
A     & 0     & 1     & 1     & 1     & 1     & 1 \\
B     & 1     & 0     & 1     & 1     & 1     & 1 \\
C     & 1     & 1     & 0     & 1     & 1     & 1 \\
D     & 1     & 1     & 1     & 0     & 1     & 1 \\
E     & 1     & 1     & 1     & 1     & 0     & 1 \\
F     & 1     & 1     & 1     & 1     & 1     & 0 \\
\end{block}%
\end{blockarray}%
\]


\[
\left[
\begin{smallmatrix}
0     & 1     & 1     & 1     & 1     & 1 \\
1     & 0     & 1     & 1     & 1     & 1 \\
1     & 1     & 0     & 1     & 1     & 1 \\
1     & 1     & 1     & 0     & 1     & 1 \\
1     & 1     & 1     & 1     & 0     & 1 \\
1     & 1     & 1     & 1     & 1     & 0 \\
\end{smallmatrix}%
\right]
\]

\end{document}

Answer 1

This relies on the requirement that all columns in the matrix are of equal width. In addition, the value of \? (here a kern of 1.1pt) and the global kern to the header (here 9mu) might need adjustment based on the case.

This answer is based on my result here: braces over matrix

The fact that the natural width of cap letters is different than the natural width of digits allows two approaches:

1. stretch the column gap between digits

2. compress the column gap between letters

Here is approach 1:

\documentclass[12pt]{article}%
\usepackage{amsmath}
\usepackage{blkarray}
\usepackage{amsmath}
\usepackage{stackengine}
\begin{document}
\[
\begin{blockarray}{ccccccc}
      & A     & B     & C     & D     & E     & F \\
\begin{block}{c[cccccc]}
A     & 0     & 1     & 1     & 1     & 1     & 1 \\
B     & 1     & 0     & 1     & 1     & 1     & 1 \\
C     & 1     & 1     & 0     & 1     & 1     & 1 \\
D     & 1     & 1     & 1     & 0     & 1     & 1 \\
E     & 1     & 1     & 1     & 1     & 0     & 1 \\
F     & 1     & 1     & 1     & 1     & 1     & 0 \\
\end{block}%
\end{blockarray}%
\]
\def\tmp{%
  \def\?{\kern1.1pt}
  \begin{smallmatrix}
\?0     \?&\? 1     \?&\? 1     \?&\? 1     \?&\? 1     \?&\? 1 \?\\
1     & 0     & 1     & 1     & 1     & 1 \\
1     & 1     & 0     & 1     & 1     & 1 \\
1     & 1     & 1     & 0     & 1     & 1 \\
1     & 1     & 1     & 1     & 0     & 1 \\
1     & 1     & 1     & 1     & 1     & 0 \\
 \end{smallmatrix}
}%
\[
\stackMath\def\stackalignment{r}%
  \stackon%
    {\begin{smallmatrix}A\\B\\C\\D\\E\\F\end{smallmatrix}\!\left[\tmp\right]}%
    {\stackon[1pt]{\phantom{\smash{\tmp\mkern -36mu}}}{%
    \begin{smallmatrix}A&B&C&D&E&F\end{smallmatrix}}\mkern 9mu}%
\]
\end{document}

and here is approach 2:

\documentclass[12pt]{article}%
\usepackage{amsmath}
\usepackage{blkarray}
\usepackage{amsmath}
\usepackage{stackengine}
\begin{document}
\[
\begin{blockarray}{ccccccc}
      & A     & B     & C     & D     & E     & F \\
\begin{block}{c[cccccc]}
A     & 0     & 1     & 1     & 1     & 1     & 1 \\
B     & 1     & 0     & 1     & 1     & 1     & 1 \\
C     & 1     & 1     & 0     & 1     & 1     & 1 \\
D     & 1     & 1     & 1     & 0     & 1     & 1 \\
E     & 1     & 1     & 1     & 1     & 0     & 1 \\
F     & 1     & 1     & 1     & 1     & 1     & 0 \\
\end{block}%
\end{blockarray}%
\]
\def\tmp{%
  \begin{smallmatrix}
0     & 1     & 1     & 1     & 1     & 1 \\
1     & 0     & 1     & 1     & 1     & 1 \\
1     & 1     & 0     & 1     & 1     & 1 \\
1     & 1     & 1     & 0     & 1     & 1 \\
1     & 1     & 1     & 1     & 0     & 1 \\
1     & 1     & 1     & 1     & 1     & 0 \\
 \end{smallmatrix}
}%
\[
\stackMath\def\stackalignment{r}%
{\def\?{\kern-1.2pt}
  \stackon%
    {\begin{smallmatrix}A\\B\\C\\D\\E\\F\end{smallmatrix}\!\left[\tmp\right]}%
    {\stackon[1pt]{\phantom{\smash{\tmp\mkern -36mu}}}{%
    \begin{smallmatrix}A\?&\?B\?&\?C\?&\?D\?&\?E\?&\?F\end{smallmatrix}}\mkern 9mu}}%
\]
\end{document}