How can I typeset non-square matrices?

I'd like to typeset a non-square matrix in the manner of $\begin{array}$, but I don't know how. How can I typeset a 4 x 3 matrix, for example?

• Welcome to TeX.SX! If you know array I don't understand the problem. Just specify three columns, and add four rows ... – Torbjørn T. Apr 2 '16 at 22:30
• Thank you! I tried doing this but got a "! Paragraph ended before \partialderivative was complete." error when I tried to compile (it's a matrix of partial derivatives). – Mathmank Apr 2 '16 at 22:36
• Could you post a minimal (non-)working example? – Bernard Apr 2 '16 at 22:42
• So I tried 'array' with just simple letters for entries and it worked, so the error must be elsewhere. I'll make this a separate question I guess. Thanks for the help! – Mathmank Apr 2 '16 at 22:43

Load amsmath and type, say:
$\begin{bmatrix} a&b&c\\ d&e&f\\ g&h&i\\ k&l&m \end{bmatrix}$

if you want a bracketed matrix, pmatrix for a matrix with parentheses, vmatrix for a determinant or Vmatrix for a matrix with double rules.
Loading mathtools (needless to load amsmath in this case), you may use the \b-p-v-Vmatrix* environments, which allows you to specify the alignment of columns: [r], [l] or [c] (default).