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    this is a stupid post, but I am quite stupid using technology in general. Already here 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.

    • CommentAuthorWill Jagy
    • CommentTimeNov 25th 2011 edited
    If it is in Tex, the only change needed is to change the double backslashes \\ at the end of rows to triple backslashes, \\\

    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
    \right) ,

    $$ A_3 \; = \;
    \left( \begin{array}{rrr}
    1 & 1 & 0 \\\
    0 & 1 & 1 \\\
    0 & 0 & 1
    \right) ,

    $$ A_4 \; = \;
    \left( \begin{array}{cccc}
    0 & -1 & 1 & 0 \\\
    1 & 0 & 0 & 1 \\\
    0 & 0 & 0 & -1 \\\
    0 & 0 & 1 & 0
    Oh thank you very much. I'll try right away. In case of problems I will write again.
    it works!! thank you very much again!
    • CommentAuthorgrp
    • CommentTimeNov 25th 2011
  is a place where you can create a user and test out posts for MathOverflow and work out the bugs. You can also view source in posts that you like and copy (hopefully) fragments and modify them. For posts that are edited, you can click on the time of last edit to get to (links to) the source.

    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


    I believe that MathJax supports the {matrix} environment actually.

    • CommentAuthortheojf
    • CommentTimeNov 26th 2011
    Be careful with \; — the backslash there might also get swallowed. (I know that backslashes often get swallowed before commas.)

    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.)