mathastext font shapes rendered in wrong encoding

Question

I am trying to use the mathastext package to replace alphabet letters in math with the default fonts in the document, and gfsdidot (udidot) for greek. I can either get everything relevant except greek working, or get greek working but break latin.

I use pdfLaTeX, and I think I have enough math alphabets, so that shouldn't be the issue. I also know that GFS Didot comes in all desired weights and shapes. How does an alphabet in mathastext know that it is only meant for greek and why does it not contain \mathrm? What is its relation to \mathnormal (which currently is equally broken)?

\Mathrm may seem like a syntax error but it is defined internally in mathastext.sty, though I am not sure how (or if) to properly use it.

If it's any help to convey what I am looking to do: something akin to what unicode-range does in CSS, to use one font for one range of characters, and another font for another range. For pdfLaTeX this seems to get harder because fonts are not in unicode, but it should indeed be possible, because mathastext does so properly for the default math alphabet. How?

\documentclass{article}
\usepackage[LGR,T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{ebgaramond}
\usepackage[LGRgreek,italic]{mathastext}

\DeclareSymbolFont{mycustom}{LGR}{udidot}{normal}{n}
\SetSymbolFont    {mycustom}{normal}{LGR}{udidot}{\rmdefault}{n}%
\DeclareSymbolFontAlphabet{\Mathrm}{mycustom}%%% disable this to break greek but fix latin

\MTgreekfont{udidot}
\MTitgreek
\MTitGreek
\Mathastext

\newcommand*{\GRALPH}{\alpha \beta \gamma \delta \epsilon
\zeta \eta \theta \iota \kappa \lambda \mu \nu \xi o \pi
\rho \sigma \tau \upsilon \phi \chi \psi \omega \varsigma}

\newcommand*{\gralph}{A B \Gamma \Delta E Z H \Theta I K
\Lambda M N \Xi O \Pi P \Sigma T \Upsilon \Phi X \Psi \Omega}

\begin{document}

\noindent
\( \GRALPH - \mathrm{\GRALPH} \)\\
\( \gralph - \mathrm{\gralph} \)\\
so far it looks good, but now also latin turns up as greek:\\
\( abcdefghijklmnopqrstuvwxyz - \mathrm{abcdefghijklmnopqrstuvwxyz} \)

\end{document}

Answer 1

I think you would like \mathrm to turn the Greek letters upright. The \Mathrm is a math alphabet defined by mathastext designed to use the text font (which is already used for the letters in math) in the default shape, which a priori is upright. (so this makes sense if the package received italic option). Then \mathrm is simply re-defined to be the macro with meaning \Mathrm (so option defaultmathalphabets is implemented by just not doing that definition).

In LaTeX NFSS, \mathrm means to use the text font in math. It doesn't mean to turn things upright. In particular it makes no sense, a priori, to expect it to turn Greek letters from italic to upright shape.

But you can define a math alphabet command \upgreek which will use a given font in LGR encoding having upright Greek letters. Indeed, mathastext makes sure the Greek letters obey math alphabet commands.

So, possibly, this achieves what you want:

\documentclass{article}
\usepackage[LGR,T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{ebgaramond}
\usepackage[LGRgreek,italic]{mathastext}
\MTitgreek
\MTgreekfont{udidot}
\Mathastext

\DeclareSymbolFont{mycustom}{LGR}{udidot}{m}{n}
\DeclareSymbolFontAlphabet{\upgreek}{mycustom}

\newcommand*{\GRALPH}{\alpha \beta \gamma \delta \epsilon
\zeta \eta \theta \iota \kappa \lambda \mu \nu \xi o \pi
\rho \sigma \tau \upsilon \phi \chi \psi \omega \varsigma}

\newcommand*{\gralph}{A B \Gamma \Delta E Z H \Theta I K
\Lambda M N \Xi O \Pi P \Sigma T \Upsilon \Phi X \Psi \Omega}

\begin{document}

\noindent
\( \GRALPH - \upgreek{\GRALPH} \)\\
\( \gralph - \upgreek{\gralph} \)\\
so far it looks good.\\
\( abcdefghijklmnopqrstuvwxyz - \mathrm{abcdefghijklmnopqrstuvwxyz} \)

\meaning\mathrm
\end{document}

Unfortunately \mathrm{\upgreek{\alpha\beta ab}} will not work, because the \upgreek will override the exterior \mathrm. LaTeX math alphabets just don't nest.

If you need a macro \uprightlatinandgreek then it might be possible, but if you don't I can rest a bit ;-).