Re: [bug][ox-latex] Captions in equations

[Rasmus <rasmus@gmx.us>]

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Nicolas Goaziou <n.goaziou@gmail.com> writes:

> Hello,
>
> Rasmus <rasmus@gmx.us> writes:
>
>> This example produces invalid LaTeX code:
>>
>> #+CAPTION: test
>> #+ATTR_LATEX: :mode math :environment pmatrix
>> | \alpha | \beta | \gamma |
>>
>> Namely,
>>
>> \begin{equation}
>> \caption{test text}
>> \mathbf{H}=\begin{pmatrix}
>>  \vdots & 0 & \vdots \\
>>  \vdots & H & \vdots \\
>>  \vdots & 0 & \vdots \\
>> \end{pmatrix}.
>> \end{equation}
>>
>> But an equation cannot have a caption.
>>
>> I'm not sure what the desired behavior is.  (i) To silently drop the
>> caption, (ii) to wrap the equation in some sort of float and give it a
>> caption; or (iii) to print the text sans the \caption{·}.
>>
>> (iii) can be archived with math-prefix.  (ii) is a bit weird, but
>> could be archived relatively easy, but it's not really what one would
>> expect; it's consistent with how captions work for tables (turned into
>> a float when a caption is present).  (i) is also a bit weird, but
>> seems the most reasonable to me.
>>
>> Since I don't know what the correct behavior is, I don't have a patch
>> right now.
>
> As a short term solution, I think the (i) is the best. That's exactly
> what happens to LaTeX environments: in `org-latex-latex-environment',
> the caption is dropped and only the label, if any, is inserted in the
> environment.

OK.  I can prepare a patch.

> As a long term solution, it would be interesting to be able to do (ii),
> for both tables in math mode (but not in inline-math) and LaTeX
> environments: captioning an equation is a reasonable request.

Indeed this seems long-term.

I have only rarely seen math-floats.  It is, however, sometimes used
in elsarticle.cls from the Elsevier publishing house.  See this
example:

    http://bayimg.com/aAHDfAAFE

Here the caption can be seen as the text below the equation, ("Where
Λ(·) is...")  and (16) is the reference.  The attached file play
around with some preliminary LaTeX styles for this.

In LaTeX the floating would be kind of odd, I think.  At the very
least math floats shouldn't be Figure or Tables (IMO); unfortunately
the Internets seem to suggest that you usually create additional
floats via packages such as newfloat of "caption".  HTML should also
be considered...

–Rasmus

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\documentclass[11pt]{article}
\usepackage{amsmath}
\begin{document}
first equation
\begin{equation}
  x=1
\end{equation}

Second equation
\par\noindent\fbox{\parbox{\textwidth}{
  \begin{equation}
    x=2\Lambda(x)
  \end{equation}
  Here, $\Lambda(\cdot)$ is \dots}}

\begin{figure}
  \fbox{\parbox{\textwidth}{\[g=3\]}}\caption{Third caption}
\end{figure}

\end{document}