Questions about \fbox

Question

I would like to put a text and a math formula inside a \fbox, but I got an error:ERROR: LaTeX Error: Something's wrong--perhaps a missing \item. Also the\\ did not work, so the text and the formula are still in one line.

\begin{figure}[htbp]
\centering
\fbox{%
  text\\
  $\begin{cases}
    abcdefghijklmn\\
    cdefg
   \end{cases}$
\caption{a_caption}
\label{a_label}
\end{figure}

Another question is that it seems that the width of the frame is up to the width of what I put inside fbox, what to do if I want the width to be the width of the page?

Could anyone help? Thank you very much!

Few issues: You are using inline math with the $$ and yet trying to insert a newline \\. Also the underscores will need to be escaped as in a\_caption. — Peter Grill, Aug 11 '11 at 20:49
@Herbert: I get Missing $ inserted. if I don't escape the underscores. — Peter Grill, Aug 11 '11 at 21:08

score 4 · Answer 1 · answered Aug 11 '11 at 20:55

you have to use a parbox if you want a linebreak inside fbox. E.g. with package varwidth:

\fbox{\varwidth{\linewidth}%       
text\\       
$\begin{cases}         
   abcdefghijklmn\\         
   cdefg        
 \end{cases}$\endvarwidth}

enter image description here

score 4 · Accepted Answer · edited Jul 15 '17 at 14:27

Regarding \fbox, as Joseph said: there's a closing brace missing, determining the end of the argument.

For the whole text width you could use the framed package and its environment with the same name, such as

\usepackage{framed}
...
\begin{figure}[htbp]
\begin{framed}
  \centering
  text\\
  $\begin{cases}
    abcdefghijklmn\\
    cdefg
   \end{cases}$
\end{framed}
\caption{a caption}
\label{a_label}
\end{figure}

Another option is the improved version mdframed.
For framing math environments, there's the \boxed command of amsmath.

Questions about \fbox

2 Answers2

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