A note on tex4ht conversion of displayed math using AMSMATH environment align and flalign

Nasser M. Abbasi

November 10, 2009

The following zip file contains a very small example which shows this problem. It includes the command used (in the .bat file), the tex4ht.env file on my computer, and the html output and the .lg file and the commands displayed on the DOS window. May be this will allow someone to more easily find a solution to this problem. short_example.zip

Using MikTex 8.2 on windows XP with tex4ht included in this installation, I noticed the following problem: When converting displayed math using the \begin{align*}...} environment, then part of the generated mathematics will be converted bit-mapped images and part will be left in text. This causes the equations to not look as good as they should be.

To start with, when using inline math with tex4ht, this problem allready has a known solution (see Dr Philip A. Viton page in the reference below). Assume the tex4ht configuration file is called foo.cfg, then in order to force tex4ht to convert the equation to bit-mapped image for inline math one needs to add the following 2 lines to this file:

  \Preamble{html}
  \begin{document}
  \Configure{$}{\PicMath}{\EndPicMath}{}
  \Configure{PicMath}{}{}{}{ class="math" align="absmiddle"}
  \EndPreamble

In addition, to make the displayed math images larger so that they will be easier to see, I found that I need to change the following 3 lines in tex4ht.env file to increase the magnification to 1.4 from what it would be otherwise. This has no effect on this problem. This only allows the bit-mapped images to become larger that is all.

  Gdvips  -E -q -Ppdf -f %%1 -pp %%2 > zz%%4.ps
  Gdvips  -Ppdf -mode ibmvga -D 110 -f %%1 -pp %%2 > zz%%4.eps
  Gdvips  -E -Ppdf -mode ibmvga -D 110 -f %%1 -pp %%2 > zz%%4.ps

  Gdvips -x 1400  -E -q -Ppdf -f %%1 -pp %%2 > zz%%4.ps
  Gdvips -x 1400  -Ppdf -mode ibmvga -D 110 -f %%1 -pp %%2 > zz%%4.eps
  Gdvips -x 1400  -E -Ppdf -mode ibmvga -D 110 -f %%1 -pp %%2 > zz%%4.ps

htlatex foo.tex "foo.cfg,htm"

Then the result of something as $v=l\dot{\theta}$}will be to show as $˙ v = lθ$ . This equation is all in one bitmapped image.

The problem comes when using multiline display math. When using the environment \begin{align*}...\end{align*}}then tex4ht will not convert all the equations to one bit-mapped image. This can cause a problem as can be seen in this example.

  \begin{align*}
  v^{2}   & =\left(  \dot{x}+v_{x}\right)  ^{2}+v_{y}^{2}\\
             &  =\dot{x}^{2}+l^{2}\dot{\theta}^{2}+2\dot{x}l\dot{\theta}\cos\theta
  \end{align*}

  \begin{flalign*}
  v^{2}    &=\left(  \dot{x}+v_{x}\right)  ^{2}+v_{y}^{2}\\
              &=\dot{x}^{2}+l^{2}\dot{\theta}^{2}+2\dot{x}l\dot{\theta}\cos\theta
  \end{flalign*}

There is no solution that I know of at the time writing this. Tex4ht simply does not like the amsmath align environment for some reason. A tex4ht expert is needed to solve this problem.

But I have found a work around. Instead of using the above environments, use \begin{eqnarray*}...\end{eqnarray*}}.For some reason, in this case tex4ht will use bit-mapped image for all of the multiline display as can be see in the following output

  \begin{eqnarray*}
  v^{2}  &=& \left(  \dot{x}+v_{x}\right)  ^{2}+v_{y}^{2}\\
            &=& \dot{x}^{2}+l^{2}\dot{\theta}^{2}+2\dot{x}l\dot{\theta}\cos\theta
  \end{eqnarray*}

2 2 2 v = (˙x+ vx) + vy = ˙x2 + l2˙θ2 + 2˙xlθ˙cosθ

  \begin{equation*}
  \begin{split}
  v^{2}  &  =\left(  \dot{x}+v_{x}\right)  ^{2}+v_{y}^{2}\\
            &  =\dot{x}^{2}+l^{2}\dot{\theta}^{2}+2\dot{x}l\dot{\theta}\cos\theta
  \end{split}
  \end{equation*}

v²	= ² + v_y²
	= ẋ² + l²² + 2ẋlcosθ

v²	= ² + v_y²
	= ẋ² + l²² + 2ẋlcosθ