pmatrix not rendering correctly -- possibly a wileySix problem

Question

Original post below A couple of people asked for a whole document:

\documentclass{wileySix}
\usepackage{amsmath}   
\usepackage{amsfonts}
\usepackage{amssymb}

\begin{document}
 \[
 \mathbf{y}=
 \begin{pmatrix}
y_1 \\
y_2
\end{pmatrix}\mbox{ and }
\boldsymbol{\mu}=\begin{pmatrix}
\mu_1 \\
\mu_2
\end{pmatrix}
\]

\end{document}

This problem goes away when the documentclass is changed from wileySix to article. I will investigate.

Original post Hi I would like to write the following expression in LaTeX using pmatrix

I can do this with standard older TeX:

\mathbf{y}=\left(\begin{array}{c} y_1 \\ y_2
\end{array} \right)  \mbox{ and }  \boldsymbol{\mu}=
\left(\begin{array}{c} \mu_1\\ \mu_2
\end{array} \right)

However, I think I should be able to do this much more neatly with using pmatrix from the amsmath package:

\mathbf{y}=
\begin{pmatrix}
y_1 \\ y_2
\end{pmatrix}\mbox{ and }
\boldsymbol{\mu}=\begin{pmatrix}
\mu_1 \\ \mu_2
\end{pmatrix}

What I end up with in the rendered document is this

which clearly has problems. I'm running on MacTeX, but that has never caused me problems elsewhere. Any advice would be appreciated

Answer 1

The wileysix class redefines \@array in a small but decisive detail:

LaTeX kernel definition

\def\@array[#1]#2{%
  \if #1t\vtop \else \if#1b\vbox \else \vcenter \fi\fi
  \bgroup
  \setbox\@arstrutbox\hbox{%
    \vrule \@height\arraystretch\ht\strutbox
           \@depth\arraystretch \dp\strutbox
           \@width\z@}%
  \@mkpream{#2}%
  \edef\@preamble{%
    \ialign \noexpand\@halignto
      \bgroup \@arstrut \@preamble \tabskip\z@skip \cr}%
  \let\@startpbox\@@startpbox \let\@endpbox\@@endpbox
  \let\tabularnewline\\%
    \let\par\@empty
    \let\@sharp##%
    \set@typeset@protect
    \lineskip\z@skip\baselineskip\z@skip
    \ifhmode \@preamerr\z@ \@@par\fi
    \@preamble}

wileysix.cls definition

\def\@array[#1]#2{%
  \if #1t\vtop \else \if#1b\vbox \else \vcenter \fi\fi
  \bgroup
  \setbox\@arstrutbox\hbox{%
    \vrule \@height\arraystretch\ht\strutbox
           \@depth\arraystretch \dp\strutbox
           \@width\z@}%
  \@mkpream{@{}#2@{}}%
  \edef\@preamble{%
    \ialign \noexpand\@halignto
      \bgroup \@arstrut \@preamble \tabskip\z@skip \cr}%
  \let\@startpbox\@@startpbox \let\@endpbox\@@endpbox
  \let\tabularnewline\\%
    \let\par\@empty
    \let\@sharp##%
    \set@typeset@protect
    \lineskip\z@skip\baselineskip\z@skip
    \ifhmode \@preamerr\z@ \@@par\fi
    \@preamble}

The difference is in the line

  \@mkpream{#2}%

that becomes

  \@mkpream{@{}#2@{}}%

so that no padding is added at the left and right of an array. On the other hand, amsmath manually fixes the padding in matrices, by adding a negative space between the fences and the matrix:

\renewenvironment{matrix}{%
  \matrix@check\matrix\env@matrix
}{%
  \endarray \hskip -\arraycolsep
}
\def\env@matrix{\hskip -\arraycolsep
  \let\@ifnextchar\new@ifnextchar
  \array{*\c@MaxMatrixCols c}}
\renewenvironment{pmatrix}{%
  \left(%
  \matrix@check\pmatrix\env@matrix
}{
  \endmatrix\right)%
}

The \hskip -\arraycolsep are exactly the negative spaces I was talking about. The one on the right has its effect, because the standard preamble of a matrix is specified and the last column is not reached until the matrix has \MaxMatrixCols columns.

I find the redefinition in the class very silly: it is done exactly for the same purpose of amsmath, that is, not having a gap between the fences and the coefficients of the matrix. But the cure is worse than the disease.

I see no real problem in fixing the meaning of \@array to be the kernel one. Just remember to manually add @{} at either side of an array column specification in cases you use the environment for special matrices with non standard center alignment.

\documentclass{wileysix}
\usepackage{amsmath}   
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{etoolbox}

\makeatletter
\patchcmd{\@array}{\@mkpream{@{}#2@{}}}{\@mkpream{#2}}{}{}
\makeatother

\begin{document}
 \[
 \mathbf{y}=
 \begin{pmatrix}
y_1 \\
y_2
\end{pmatrix}\mbox{ and }
\boldsymbol{\mu}=\begin{pmatrix}
\mu_1 \\
\mu_2
\end{pmatrix}
\]
\end{document}