Conflict between eqnarray and tabstackengine

Question

I seem to be getting conflict between the eqnarray environment and the tabstackengine package (which is very useful for matrices, column vectors, etc.).

\documentclass{report}
\usepackage{tabstackengine}

\begin{document}

\begin{eqnarray*}
  v &=& \bracketMatrixstack{1 & 2 \\ 3 & 3} \bracketVectorstack{-3 \\ 2} \\
  a &=& b 
\end{eqnarray*}

\end{document}

I get about a million errors if I try to compile this!

Answer 1

The error has nothing to do with eqnarray (which should not be used anyway) apart from it being an alignment environment.

The problem is that tabstackengine doesn't protect the internal & from a possible outer alignment.

Just brace the matrix:

\documentclass{report}
\usepackage{amsmath}
\usepackage{tabstackengine}

\begin{document}

\begin{align*}
  v &= {\bracketMatrixstack{1 & 2 \\ 3 & 3}} \bracketVectorstack{-3 \\ 2} \\
  a &= b
\end{align*}

\end{document}

I'm not sure how this is better than

\documentclass{report}
\usepackage{amsmath}

\begin{document}

\begin{align*}
  v &= \begin{bmatrix} 1 & 2 \\ 3 & 3 \end{bmatrix} 
       \begin{bmatrix} -3 \\ 2 \end{bmatrix} \\
  a &= b
\end{align*}

\end{document}

You can fix tabstackengine:

\documentclass{report}
\usepackage{amsmath}
\usepackage{tabstackengine}

\makeatletter
\renewcommand\ensureTABstackMath[1]{%
  {\ifnum`}=\z@\fi
  \let\sv@TABmode\TAB@delim\TABstackMath#1\let\TAB@delim\sv@TABmode
  \ifnum`{=\z@\fi}%
}
\makeatother

\begin{document}

\begin{align*}
  v &= \bracketMatrixstack{1 & 2 \\ 3 & 3} \bracketVectorstack{-3 \\ 2} \\
  v &= \begin{bmatrix} 1 & 2 \\ 3 & 3 \end{bmatrix}
       \begin{bmatrix} -3 \\ 2 \end{bmatrix} \\
  a &= b
\end{align*}

\end{document}

but I still can't see any improvement.