Math & Science ⇒ how to use eqnarray in savenewbox

[matthewwang]

Hi, I am trying to use \savenewbox to get the baseline when I use latex to generate png images from latex equation, but I always get failure when the equation are wrapped with \begin{eqnarray} and \end{eqnarray}, the follow is content one of the failed sample tex file:

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\documentclass[10pt]{article}
\usepackage{geometry}
\usepackage{empheq}
\usepackage{amssymb,amsmath,bm,color} 
\usepackage[latin1]{inputenc} 
\pagestyle{empty}
				
\newsavebox{\mybox}
\newlength{\mywidth}
\newlength{\myheight}
\newlength{\mydepth}
				
\setlength{\topskip}{0pt}
\setlength{\parindent}{0pt}
\setlength{\abovedisplayskip}{0pt}
\setlength{\belowdisplayskip}{0pt}
				
\begin{lrbox}{\mybox}
$\displaystyle
\begin{eqnarray}
5 + 0 &=& 5\\4 + 1 &=& 5\\3 + 2 &=& 5\\2 + 3 &=& 5\\1 + 4 &=& 5\\5 + 0 &=& 5
\end{eqnarray}
$
\end{lrbox}
				
\settowidth {\mywidth}  {\usebox{\mybox}}
\settoheight{\myheight} {\usebox{\mybox}}
\settodepth {\mydepth}  {\usebox{\mybox}}
				
\newwrite\foo
\immediate\openout\foo=\jobname.sizes
\immediate\write\foo{Depth=\the\mydepth}
\immediate\write\foo{Height=\the\myheight}
\addtolength{\myheight} {\mydepth}
\immediate\write\foo{TotalHeight=\the\myheight}
\immediate\write\foo{Width=\the\mywidth}
\closeout\foo
				
% set the paper-size and do everything in one pdflatex run
\geometry{paperwidth=\mywidth,
paperheight=\myheight,margin=0pt}
				    
\begin{document}
\usebox{\mybox}
\end{document}

my method of getting png image is using latex generate .dvi and .sizes file, then use dvipng command to generate png from .dvi file.
first step command :

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/usr/texbin/latex -output-directory=/Users/matthew/Desktop/latex/dvi -jobname=mytex mytex.tex

second step command :

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/usr/texbin/dvipng -o /Users/matthew/Desktop/latex/png/mytex.png -T tight -D 300 mytex.dvi

this approach is working well on most latex equations but always failed when the equation wrapped with \begin{eqnarray} and \end{eqnarray}, the error message is :

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Missing \endgroup inserted.
<inserted text> 
                \endgroup 
l.21 				\begin{eqnarray}

does anyone have the idea or solution to get rid of this error and make it working? My LaTex version is MacTeX-2011.

Thanks
matthew

[josephwright]

The eqnarray structure is no 'left-right' material (it's display math), and so it cannot go inside a lrbox. You should look at the standalone class to do what you want. (Side note: do not use eqnarray at all! It is defective in many ways, and is only really there for backward-compatibility.)

[matthewwang]

Hi, Joseph

Thanks for you relay, in my use case, I do really need the box to get some parameters like baseline offset, so is there any alternative to replace the eqnarray or lrbox and generate the png as expect?

cheers
Matthew