Write math and make a box with alltt environment

Question

I tried looking up for this, but I have not found a way to do both at the same time.

I would like to write math symbols in a verbatim like environment, for which I use alltt. But I would also like to have my code in a box, for which I used to use \usepackage{fancyvrb} and Verbatim environment.

Is there a way to combine both?

Answer 1

Yes, you can do that, as explained on page 16 of the fancyvrb documentation:

\documentclass{article}
\usepackage{fancyvrb}

\begin{document}

\begin{Verbatim}[commandchars=\\\{\},
codes={\catcode`$=3\catcode`^=7\catcode`_=8},frame=single]
some code test
$\sum a_i$
\end{Verbatim}

\end{document}

I'd suggest you to switch to listings and use its mathescape=true feature:

\documentclass{article}
\usepackage{listings}

\lstset{
  basicstyle=\ttfamily,
  columns=fullflexible,
  mathescape=true,
  frame=single
}

\begin{document}

\begin{lstlisting}
some code test
$\sum a_i$
\end{lstlisting}

\end{document}

If you want fancier boxes, then you could use tcolorbox and its interaction with listings.

Answer 2

The following example derived from the documentation of fancyvrb, section "4.1.6 Catcode characters".

\documentclass[a5paper]{article}
\usepackage{fancyvrb}
\begin{document}
\begin{Verbatim}[
  frame=single,
  commandchars=\\\{\},
  codes={%
    \catcode`$=3\relax
    \catcode`^=7\relax
    \catcode`_=8\relax
  },
]
x\string_0=1/sqrt(z\string^2) ! $x_0=\frac{1}{\sqrt{z^2}}$
\end{Verbatim}
\begin{Verbatim}[
  frame=single,
  commandchars=\\\{\},
  codes={%
    \catcode`$=3\relax
  },
]
x_0=1/sqrt(z^2) ! $x\sb{0}=\frac{1}{\sqrt{z\sp{2}}}$
\end{Verbatim}
\end{document}

When _ and ^ have the normal category codes, then they needed to be prefixed by \string, if they should be set in verbatim mode.

Alternatively, _ and ^ are kept unchanged and \sb and \sp are used in math mode instead.