Toggle old alignment behavior for equations

[fredrik-johansson]

Previously, if you put two equations inside one math block

.. math ::

    A

    B

both would show up centered. Due to recent changes in sphinx (which puts them in an align environment), they now render right-aligned. I can get back to two centered equations using

.. math ::

    A

.. math ::

    B

but this is less convenient. Is there any way to restore the old behavior?

[fredrik-johansson]

BTW, the workaround to get two centered equations is not perfect. Although it gives similar output to the old behavior with HTML+MathJax, it creates an extra vertical space in latexpdf output.

[tk0miya]

Indeed. It comes from #2254. I reproduce this with following code:

Single equation in single math directive:

.. math ::

    A

Multiple equations in single math directive:

.. math ::

    A

    B

Multiple equations in multiple math directives:

.. math ::

    A

.. math ::

    B

Indeed, the equations are slightly misaligned.

[jfbu]

Perhaps there is some more up-to-date info but I have already found this : http://tex.stackexchange.com/a/8142/4686, which says

for some reason, a one-line "aligned" is not properly centered. this appears to be a bug, and i am entering it as such in the amsmath bugs list.

Anyway, things are produced like

\begin{align*}\begin{aligned}
\begin{split}A\end{split}\\
\begin{split}B\end{split}\end{aligned}\end{align*}

and I am not sure about split inside aligned inside align*. The split environment is designed for use in full-width environments align, gather, or equation. The amsmath documentation doesn't have a single example of split inside aligned. Where would the & and \\ which split uses come from ?

[jfbu]

I obtain centered results with

Single equation in single math directive:
\begin{align*}\!\begin{aligned}
\begin{split}\boxed{A}\end{split}\\\end{aligned}\end{align*}
Multiple equations in single math directive:
\begin{align*}\!\begin{aligned}
\begin{split}\boxed{A}\end{split}\\
\begin{split}\boxed{B}\end{split}\\\end{aligned}\end{align*}

\noindent\rule{.5\linewidth}{3pt}%
\kern-.2pt 
\smash{\rule[-5cm]{.4pt}{10cm}}%
\kern-.2pt 
\rule{.5\linewidth}{6pt}

Multiple equations in multiple math directives:
\begin{align*}\!\begin{aligned}
\begin{split}\boxed{A}\end{split}\\\end{aligned}\end{align*}\begin{align*}\begin{aligned}
\begin{split}\boxed{B}\end{split}\\\end{aligned}\end{align*}

The recipe appears to be to use \!\begin{aligned}.....\\\end{aligned}, hence an extra \! before \begin{aligned} and an extra \\ before \end{aligned}. Not tested apart from the above.

(and I still don't understand the reason for split)

[jfbu]

In my previous comment notice that the bottom boxed B is not centered but I forgot the \! before \begin{aligned} for the last one. If one adds it, the bottom boxed B is centered.

[tk0miya]

Thank you for comment. It looks very nice!

The aligned also comes from #2254 . It is used to wrap whole of equations and give only one equation-number label.
But I don't know why aligned and split is used at same time. I did not care that.
@xuhdev Do you remember the reason?

[xuhdev]

I think it's OK to remove split inside aligned. I don't remember the exact reason, but I feel like that I added split inside aligned for semantic purpose only: split splits single equations. If it causes any issues, we can remove it.

According to @jfbu 's comments, we should use different environments for single equations (split inside equation) and multiple equations (align).

[tk0miya]

I fixed this at 39396a4 and 3206ccb.

Finally I use equation and split for single equation and align and aligned for multiple equations.
If you find another problem, please let me know.

Thanks!