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.

egreg · Accepted Answer

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).

Davislor · Answer

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.

newcommandparam[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.

newcommandparam[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{ttfamilyselectfontalpha} or textnormal{ttfamilyselectfonttextalpha} in text mode, the same command will work in math mode as well.

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

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