How do I left-align entries in a matrix with \begin{matrix}?

Question

I'd like to left align -1 entry in the following matrix so that the 1s line up. Is there a way to get matrices to ignore signs in that way?

\begin{matrix}
    1 & 1  \\
    1 & -1 \\
\end{matrix}

Using \flushright{-1} doesn't seem to work.

Answer 1

A quick way to do this is by adding phantom characters:

\begin{matrix}
    1 & \phantom{-}1  \\
    1 & -1 \\
\end{matrix}

Although for simple arrays like this it's probably simpler just to use a standard array environment

\begin{array}{rr}
    1 & 1  \\
    1 & -1 \\
\end{array}

for the same result. Note that if you need control over alignment, then array is the preferred way to typeset matrices (you can simply wrap in \left( ... \right) etc. for brackets and lines).

Answer 2

If you using LaTeX2e out of the box, you can use the array environment, which is similar to a tabular:

\documentclass{article}
\begin{document}
\[
\begin{array}{rr}
    1 &  1  \\
    1 & -1 \\
\end{array}
\]
\end{document}