A more robust solution than judiciously adding extra backslashes is to protect the equation with <p> and </p>. Markdown, the offending software in question, does not process anything between those tags. This means you won't have *s and _s for emphasizing words. If you need them, <i>...</i> and <b>...</b> are still honored by most web browsers, although I think they are no longer part of modern html.

(Finally, note that this meta forum also runs Markdown, but does other sanitization first, so to test things, use faketestsite, not meta.)]]>

If it weren't against MathOverflow policy, I would post a question like "What sample TEX\Markdown has been useful to you on MathOverflow that you would like to share?" Many of the common questions as well as many of the less common questions might get resolved by a post and then later turned into a handy if somehwat limited reference. Or someone could assemble the answers provided on meta into something useful.

Gerhard "If Wishes Were Action Items" Paseman, 2011.11.25

]]>This is because one of the many programs that chew up MO posts interprets the first backslash as a command and swallows it.

To minimize frustration, why not first try a 2 by 2 identity matrix in your post and confirm that this works. Or some other post about which you don't care...

For Example,

$$ A_2 \; = \;

\left( \begin{array}{rr}

1 & 1 \\\

0 & 1

\end{array}

\right) ,

$$

$$ A_3 \; = \;

\left( \begin{array}{rrr}

1 & 1 & 0 \\\

0 & 1 & 1 \\\

0 & 0 & 1

\end{array}

\right) ,

$$

$$ A_4 \; = \;

\left( \begin{array}{cccc}

0 & -1 & 1 & 0 \\\

1 & 0 & 0 & 1 \\\

0 & 0 & 0 & -1 \\\

0 & 0 & 1 & 0

\end{array}

\right).

$$]]>

this is a stupid post, but I am quite stupid using technology in general. Already here http://mathoverflow.net/questions/80777/what-is-a-continuous-path I had some problem to include a matrix in MO: I copied-pasted from by Tex file, but it didn't work.

How can I include a matrix?

Thanks in advance.

Valerio]]>