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The term $\chi_{{}^{*}P}({}^{*}r)$ can display properly in the question, but when I paste it in a comment, it become something like: enter image description here

which is the same as \chi_{{}^{}P}({}^{}r), when $$ eliminated.

The code is:

enter image description here

I've tried it on Firefox, and Chrome, and there's no difference. What is wrong?

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  • $\begingroup$ $\chi_{{}^{*}P}({}^{*}r)$ $\endgroup$ – Metta World Peace May 10 '13 at 10:52
  • $\begingroup$ Needs a space: $\chi_{{}^{}P} ({}^{}r)$ $\endgroup$ – J. M. isn't a mathematician May 10 '13 at 11:02
  • $\begingroup$ @J.M. I'm not sure. There's no problem in displaying $\chi_P(r)$. But when I want to add a star to $P$ and $r$, it's kind of different. $\endgroup$ – Metta World Peace May 10 '13 at 11:12
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    $\begingroup$ Use \ast. $P\ast q$ $\endgroup$ – J. M. isn't a mathematician May 10 '13 at 11:15
  • $\begingroup$ @J.M. Ah,yes!! That works. Thank you. $\endgroup$ – Metta World Peace May 10 '13 at 11:17
  • $\begingroup$ @J.M.: I think this is useful information. Why don't you promote your comment to an answer? $\endgroup$ – robjohn♦ May 10 '13 at 12:59
  • $\begingroup$ @rob, I was hoping Metta can answer his own question now. Oh well... $\endgroup$ – J. M. isn't a mathematician May 10 '13 at 13:00
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Using \ast seems to work nicely, as \chi_{{}^{\ast}P}({}^{\ast}r) gives $\chi_{{}^{\ast}P}({}^{\ast}r)$

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It looks like the interaction of Markdown being performed before MathJax runs, so the two stars end up being turned into marks for italics, and MathJax doesn't process the equation because it contains internal HTML. J.M.'s solution gets you around that. You could also use \* since that will prevent Markdown from processing the star (and also remove the \ so that it is just a * when MathJax sees it).

Note that you don't need to do this in the question or answer (just comments), because the comments use a different processor than questions and answers. The Q&A processor has a much more sophisticated understanding of the interaction between MathJax and Markdown, and protects math from Markdown processing.

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