peccavi_2006 wrote:
Checking my preamble, I've got
\usepackage{graphicx,amssymb,amstext,amsmath}
(sorry if that doesnt answer your question - I'm not really sure how it works, I'm using the standard set-up the uni gives me)
Maybe you should consider \usepackage{amscd} (\begin{CD}...\end{CD}, only support squares (horizontal & vertical arrows)) or \usepackage[all]{xy} (\xymatrix{...}, more programmer friendly) or \usepackage{tikz}\usetikzlibrary{matrix,arrows} (or the tikz-cd package which makes it a little easier, very user-friendly (e.g. "bend left" as oppose to ^/1em/ or something in xymatrix)). You might need to download the package(s) from CTAN. There are official documentation on CTAN, and unofficial guides in many places if you google --- for example, J.S. Milne has got a
guide to commutative diagrams.
Doing commutative diagrams bare-hand with array/picture environment is painful. Don't do it unless you absolutely have to.