# Matrices display in preview but not after posting

If you look at my answer to

How to quickly estimate a lower bound on correlation for a large number of stocks?

you will see that I tried posting a 3x3 matrix using \begin{matrix}...\end{matrix}. It showed up fine in the preview, but scrunched into a single line after I posted it. As a quick hack I edited the post to insert some semicolons,