# Positive and Negative power in matrices and fixed size

I'd like to create a matrix that has some positive power and negative power. I'd like to have an alignment to right, so for example:

\begin{array}{rr}
3 \times 10^3 & 2 \times 10^3 \\
3 \times 10^{-3} & 2 \times 10{-3}
\end{array}


In this case, the column alignment isn't good, because the negative sign at the exponent takes a little space, so the numbers aren't aligned. How can I fix this? (I think I should add a little space at the positive power too)

Then...is want to create 3 matrices in the page that should result aligned, indipendently from the values they have. For example if I write the previous matrix and then this:

  \begin{array}{rr}
0 & 0 \\
0 & 1
\end{array}


they won't be aligned because the second is smaller than the first. Is there a way to set a fixed size to both matrices?

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Besides the problem in the question, the given code example is not correct. The column formatting specifiers have to be within a mandatory argument instead of an optional one: \begin{array}{rr}. – Stefan Kottwitz Jan 8 '11 at 17:09
Yes, you are right. I made a mistake reporting the code.. – user2835 Jan 8 '11 at 17:13

\documentclass{article}
\usepackage{siunitx}
\begin{document}

\begin{tabular}{S[table-format=2e-1]S[table-format=2e-1]}
3e3  &  2e3 \\
3e-3 & 12e-3
\end{tabular}

\end{document}


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For matrices you could use one of the matrix environments of amsmath.

With array, you could use more columns for finer alignment. For example:

\documentclass{article}
\begin{document}
$\begin{array}{r@{}rr@{}r} 3 \times {} & 10^3 & 2 \times {} & 10^3 \\ 3 \times {} & 10^{-3} & 12 \times {} & 10^{-3} \end{array}$
\end{document}


You could even put \times into @{} to be aligned between columns.

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