Automatic switching of math font based on current text font

Question

I'm writing a document using xelatex and have set up my document fonts using fontspec as follows:

\usepackage{fontspec}
\setmainfont[Mapping=tex-text,Numbers=OldStyle]{Linux Libertine O}
\setsansfont[Mapping=tex-text,Numbers=OldStyle,Scale=MatchLowercase,SmallCapsFont={Linux Biolinum Capitals O}]{Linux Biolinum O}
\setmonofont[Mapping=tex-text,Scale=MatchLowercase]{DejaVu Sans Mono}

In my document, I'd like the math font to use either Linux Libertine or Linux Biolinum based on whether the surrounding text font is serif or sans serif. For example:

\normalfont This text is Linux Libertine as is the following math: $a^2 + b^2 = c^2$.
\sffamily This text is Linux Biolinum as is the following math: $a^2 + b^2 = c^2$.

Here's what I've tried so far and the components of the problem I'd like to solve:

1. The normal math text should be set in Linux Libertine, not Computer Modern. CM can serve as a fallback provide any glyphs that LL doesn't provide, however (e.g., large symbols and operators, but not Greek letters). The mathspec package handles this requirement fairly well.

2. If the surrounding body text is set in sans serif (this is used for tables, figures, and captions), then the math should be set in sans serif. I'd prefer this be done automatically, but I don't mind adding a \sfmath command (or the like) if necessary. Unfortunately, I couldn't figure out how to coerce mathspec into handling this part.

A few things to note:

1. Neither Linux Libertine nor Linux Biolinum have much if anything in the Unicode range for math glyphs. Therefore, the Greek letters should be pulled from the Greek alphabet block and not the math Greek block, for instance.

2. I'm not using \mathsf or the math sans alphabet to indicate anything special in this document so there won't be any confusion when the math is set in sans serif solely to match the surrounding text.

The similar questions I've found on TeX.sx appear to be for pdflatex or to make use of the \mathsf command.

Answer 1

How about using mathastext? The following uses newtx which loads libertine and all the math symbols.

\documentclass{article}

\usepackage[no-math]{fontspec}
\usepackage[libertine,osf]{newtx}
\setmonofont{DejaVu Sans Mono}[
Scale=MatchLowercase]
\usepackage[italic]{mathastext}
\Mathastext[roman]
\MTfamily{\sfdefault}
\Mathastext[sans]
\MTfamily{\ttdefault}
\Mathastext[mono]
\newcommand{\swf}[1]{\MTversion{#1}}
\newcommand{\swm}[1]{\MTversion*{#1}}
\begin{document}
\swf{sans} Sans test 123 $\sum f(x)\cdot\frac{x}{yz}+\alpha\beta$

\swf{mono} Mono test 123 $\sum f(x)\cdot\frac{x}{yz}+\alpha\beta$

\swf{roman} Roman test 123 $\sum f(x)\cdot\frac{x}{yz}+\alpha\beta$

Switch only math, but not text:

\swm{sans} Sans math test 123 $\sum f(x)\cdot\frac{x}{yz}+\alpha\beta$

\swm{mono} Mono math test 123 $\sum f(x)\cdot\frac{x}{yz}+\alpha\beta$

\swm{roman} Roman math test 123 $\sum f(x)\cdot\frac{x}{yz}+\alpha\beta$

\end{document}

Compiling with Lualatex the output looks better (better spacing)

Answer 2

The following isn't sophisticated, but it is clean:

• Create two virtual fonts that are amalgams of the maths sans and serif fonts you want, so that all the characters are in them. See topskip's explnation of how to create virtual fonts, How to create a virtual font?

With these fonts, defining \mathsf is easy. It is possible to define the maths font from outside the maths environment, for instance as described by Andrew Stacey, Change math font only in some parts of a document?.