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UPDATE: Mathjax 2.2 final has been released.

We have deployed the latest Mathjax 2.2 beta on Math.SE. As with any beta release please post an answer to this question if you find any issues. We will be monitoring this thread closely along with the authors of Mathjax to ensure this release goes smoothly.

This release includes a number of new features and increased stability with over 40 bug fixes. For a list of resolved issues included in this release please check here.

There are a number of new features included as well. One feature we will be using is the Safe-mode extension. This will provide additional sanitation to protect our users from malicious javascript injections. For a list of other additional features included in this release check here.

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    $\begingroup$ Have you enabled the AMScd support? :-) $\endgroup$
    – Asaf Karagila Mod
    May 6, 2013 at 17:54
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    $\begingroup$ Not at the moment - first things first @Asaf $\endgroup$
    – Geoff Dalgas
    May 6, 2013 at 17:57
  • $\begingroup$ You should allow \arctanh \arcsinh \arccosh, etc. $\endgroup$
    – Justin
    May 15, 2013 at 3:24
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    $\begingroup$ @gangqinlaohu: But they are really \arsinh, \artanh et cetera :-) $\endgroup$
    – Jyrki Lahtonen
    May 15, 2013 at 6:36
  • $\begingroup$ @JyrkiLahtonen Thank you; didn't realize that. $\endgroup$
    – Justin
    May 15, 2013 at 23:51
  • $\begingroup$ Is the final version deployed or are we still on beta? $\endgroup$
    – Asaf Karagila Mod
    May 21, 2013 at 21:54
  • $\begingroup$ One last thing, since the official release is out an deployed, is it possible to enable the AMScd support? It has been tested on a few pages (across the meta and the main site) and seems to work well. $\endgroup$
    – Asaf Karagila Mod
    May 24, 2013 at 19:07
  • $\begingroup$ Geoff, I thought that the AMScd package was automatically loaded, but apparently not anymore? $\endgroup$
    – Asaf Karagila Mod
    Jan 15, 2014 at 20:22

1 Answer 1

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You can experiment with the CD environment by including $\require{AMScd}$ in your post, and then using \begin{CD}...\end{CD}, as below.

Here is an example using CD:$\require{AMScd}$

\begin{CD} A @>a>> B\\@VVbV @VVcV\\ C @>d>> D \end{CD}

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    $\begingroup$ Sweet!$\vphantom{}$ $\endgroup$
    – Asaf Karagila Mod
    May 6, 2013 at 22:27
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    $\begingroup$ Also, I have to ask, why AMScd and not some other diagram drawing package? (E.g. one that allows diagonal arrows.) $\endgroup$
    – Asaf Karagila Mod
    May 6, 2013 at 22:40
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    $\begingroup$ The AMS is one of the MathJax sponsors and they asked for it, so I implemented it. Also, its syntax is limited, so is readily handled, and it can be represented naturally in MathML, the format that underlies MathJax. Something like xypic has a much more extensive syntax, and does not fit naturally into the MathML language, so is much harder to implement in MathJax (there is an XyJax project that does implement it through SVG, and it is impressive). Arbitrary diagonal and arc arrows are not easily represented in MathML, and so need an implementation outside of MathML. $\endgroup$
    – Davide Cervone
    May 6, 2013 at 23:36
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    $\begingroup$ Interesting, I figured it might be related to implementability. What are the odds of the AMS adding support for diagonal arrows? :-) $\endgroup$
    – Asaf Karagila Mod
    May 6, 2013 at 23:40
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    $\begingroup$ Not very likely, I would expect. It is not easy to do diagonal or arc arrows in TeX, either, and I think xypic uses postscript tricks to handle these things. MathJax would need to use something like SVG to do the same. While possible, it is not straight forward, and there is no MathML support for it, so it would have to be through internal extensions to MathML. I've kept that to a minimum (only one extra node type internally). $\endgroup$
    – Davide Cervone
    May 6, 2013 at 23:53
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    $\begingroup$ I'm not sure if this is the proper place to report this: If you remove the label $b$ of the first vertical arrow, i.e., if you replace @VbVV by @VVV there is extra white space added between the first row of the diagram and the start of the vertical arrows: screen shot without label $b$ and with label $b$. I'm using Safari 5.1.9 (6534.59.8) if it matters. $\endgroup$
    – Martin
    May 15, 2013 at 19:39
  • $\begingroup$ Thanks, I'll look into it. FWI, you can report bugs like that at the MathJax issue tracker. $\endgroup$
    – Davide Cervone
    May 15, 2013 at 21:11
  • $\begingroup$ It looks like this may be a problem with the code that handles isolated stretchy characters in table cells (they are supposed to stretch to the height of the row). I'll investigate further, but it probably won't make it into the v2.2 release, which is scheduled for Friday. On the other hand, using @V{}VV is sufficient to avoid the extra space, while still not showing anything as a label, so that can be used as a work-around for now. $\endgroup$
    – Davide Cervone
    May 16, 2013 at 0:18
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    $\begingroup$ We have pushed a fix for the problem to the CDN, so the arrows should work properly now, with or without labels. $\endgroup$
    – Davide Cervone
    May 24, 2013 at 22:59
  • $\begingroup$ Isn't it a bug that I have to manually insert spaces to get decent formatting in the overbraced expressions here? Also any advice on how to more cleanly do the other things there would be much appreciated (vs. the kludgey \!\!\! for right-shifting and phantom subscript for raising). $\endgroup$
    – Bill Dubuque
    Jul 13, 2019 at 15:38
  • $\begingroup$ @BillDubuque, no it is not a bug. The expressions above the overbraces and overset are treated as superscripts, which are typeset in \scriptstyle, where the spacing around operators (and most spacing) is removed or reduced. If you want the font size and spacing to be like the inline math of the rest of the expression, use \textstyle to force the superscript into the normal text typesetting rules. You can use \raise and \lower to move sub-expressions vertically, and \llap{} and \rlap{} to have them take up no horizontal space. See my next comment for an example. $\endgroup$
    – Davide Cervone
    Jul 14, 2019 at 18:25
  • $\begingroup$ @BillDubuque, For example: $$\!\!\bmod \color{#90f}{84}\colon\ 33 \equiv\overbrace{117 \equiv 165n}^{\textstyle 117 = 165n\rlap{{} + \color{#90f}{84m}}} \equiv -3n \!\overset{\raise 1pt{\textstyle {}\div\color{#c00}3}}\iff \bmod 28\colon\ \overbrace{n \equiv 33/(-3) = -11}^{\textstyle\color{#0a0}{n = -11 + 28k}}$$ $\endgroup$
    – Davide Cervone
    Jul 14, 2019 at 18:25

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