How can I use \texttt{some text} for the names of greek letters?

Question

I want to write coefficients names as alpha_0, beta_1 and phi_1 using \texttt{...} to make it look like a function arguments.

I tried \texttt{alpha_0} but I got an error ! Missing $ inserted.<inserted text>$ \item \texttt{alpha_0}. Based on https://www.tutorialspoint.com/tex_commands/texttt.htm I have tried also \texttt{\alpha_0}, \texttt{$\alpha_0$} or even similar name \texttt{alfa_0} but nothing worked for me.

Answer 1

If you want the names and the underscore

\documentclass{article}
\usepackage{amsmath}

\begin{document}

$\mathtt{alpha\_1}$

\end{document}

If you want the Greek letters

\documentclass{article}
\usepackage[LGR,T1]{fontenc}
\usepackage{amsmath}

\DeclareMathAlphabet{\mathgtt}{LGR}{cmtt}{m}{n}

\begin{document}

$\mathgtt{a_1}$
$\mathgtt{b_1}$
$\mathgtt{f_1}$

\end{document}

The picture also shows the conversion table (some characters are not easily predictable).

Answer 2

If you want an underscore, you must write it in text mode as \_. You also need to select a text font that supports Greek letters, such as New Computer Modern Mono or CMU Typewriter Text.

To use \alpha in text mode, you can load \usepackage{alphabeta}. You can also get \textalpha from \usepackage{alphabeta} or \usepackage{textgreek}.

\documentclass{article}
\tracinglostchars=2
\usepackage[default]{fontsetup} % Sets the text and math fonts to New Computer Modern Book.
\usepackage{alphabeta} % Allows \alpha, etc. in text mode.

\newcommand\param[1]{\textnormal{\ttfamily #1}}

\begin{document}
\( \param{\alpha\_0} \, \param{\beta\_1} \, \param{\phi\_1}
\)
\end{document}

An alternative is to use the \mathtt alphabet.

If you want the underscores to be subscripts, you can do this:

\documentclass{article}
\tracinglostchars=2
\usepackage[default]{fontsetup} % Sets the text and math fonts to New Computer Modern Book.

\newcommand\param[1]{\mathtt{#1}}

\begin{document}
\( \param{\mupalpha_0} \, \param{\mupbeta_1} \, \param{\mupvarphi_1}
\)
\end{document}

The correct symbol names to use are from this manual, but loading \usepackage{textgreek} and using \textalpha, etc. in math mode will work too.

For \mathtt to work in 8-bit legacy PDFTeX, you would need to find (or create) a typewriter font in OML encoding and load it with isomath. That is the only legacy TeX encoding that supports both the Greek and Latin alphabets. If you’ve loaded an 8-bit LGR font and can write \textnormal{\ttfamily\selectfont\alpha} or \textnormal{\ttfamily\selectfont\textalpha} in text mode, the same command will work in math mode as well.