Matrices with alignment

The entries of matrix columns are centered by default. Let’s see an example:

\[
  \begin{pmatrix}
    1 &  2 &  1 \\
    0 & -2 & -3 \\
    0 & 3 &  -2
  \end{pmatrix}
\]

Output:

Matrix with centered columns

For right alignment you could use an array environment instead of pmatrix. I will show a possibility to get left, right or centered alignment by redefining the internal amsmath macro \env@matrix. Its original definition in version 2.13 is:

\def\env@matrix{\hskip -\arraycolsep
  \let\@ifnextchar\new@ifnextchar
  \array{*\c@MaxMatrixCols c}}

I introduce an optional parameter, its default value is c:

\makeatletter
\renewcommand*\env@matrix[1][c]{\hskip -\arraycolsep
  \let\@ifnextchar\new@ifnextchar
  \array{*\c@MaxMatrixCols #1}}
\makeatother

Now, if you write \begin{pmatrix}[r] … above you will get:

Matrix with right aligned columns

See complete source code example.

This topic was discussed in the Matheplanet Forum.

05. May 2008 by stefan
Categories: Uncategorized | 2 comments

Comments (2)

  1. Thanks for this — I wish that it were in amslatex already!

  2. You can also use the pmatrix* environment provided by the mathtools package like this:
    begin{pmatrix*}[r]…

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