Change the textwidth in a graphic caption?

Question

Following a minimal code from somebody who asked why it produces a longer line for caption text of the figure, than a line in the main text.

\documentclass[12pt]{article}
\usepackage{array,latexsym,amsthm,amsfonts}
\usepackage[dvips,dvipdf]{graphicx,color}
\setlength{\textwidth}{7.0in} 
\setlength{\textheight}{9.0in}
\setlength{\oddsidemargin}{-.25in} 
\setlength{\topmargin}{0in}
\setlength{\tabcolsep}{0.09in}

\title{test}
\begin{document}

\maketitle

aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa 


\begin{figure}[h,t,b]
\includegraphics[scale=.25]{b.eps}
\caption{The triangular lattice with faces labelled as close-packed (C) and empty (O), the corresponding planar modification, and its generator.}
\end{figure}

\end{document}

I failed to reproduce the problem he has. But I think the solution may be to set up the textwidth for the figure caption, to match it with the textwidth in the main text.

So I wonder how to set the textwidth for the figure caption?

Answer 1

You can use the floatrow package and set wider margins for the floating environments:

\documentclass[12pt]{article}
\usepackage[demo]{graphicx}

\usepackage{floatrow}
\setfloatmargins{\hspace{-0.5in}}{\hspace{-0.5in}}

\title{test}
\begin{document}

\maketitle

aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa aaa
aaa aaa aaa


\begin{figure}[htb]
\centering
\includegraphics[scale=.25]{b.eps}

\caption{The triangular lattice with faces labelled as close-packed (C) and empty (O),
the corresponding planar modification, and its generator.}

\end{figure}

\end{document}

I've used the demo option just to provide a mock illustration, don't use it yourself. Note however that latexsym is obsolete and amssymb should be used instead (which loads amsfonts). Also the options dvips and dvipdf shouldn't be passed to graphicx or color.

The positioning specifier can be [htb], without commas.