Why can't I use my font with unicode-math?

Question

\documentclass{article}
\usepackage{unicode-math}

\setmathfont{Latin Modern Sans}

\usepackage{mwe}
\blindmathtrue

\begin{document}
\Blinddocument
\end{document}

The above fails with the error

ERROR: Internal error: bad native font flag in `map_char_to_glyph'

--- TeX said ---
--- HELP ---
No help available

What is causing this error and how can I pick fonts to avoid this in the future?

Answer 1

You have two options to overcome this issue.

1. Use an OpenType Math Font

For unicode-math to work you have to use an OpenType font which provides the math table, such as Latin Modern Math. This unfortunately defeats the implicit purpose of your MWE to use a sans serif font for maths.

\documentclass{article}
\pagestyle{empty}
\usepackage{unicode-math}
\setmathfont{Latin Modern Math}
\begin{document}
Lorem ipsum
\[ \sum_{k=0}^\infty a_0q^k = \lim_{n\to\infty}\sum_{k=0}^n a_0q^k =
            \lim_{n\to\infty} a_0\frac{1-q^{n+1}}{1-q} = \frac{a_0}{1-q} \]
dolor sit amet
\end{document}

2. Use the mathspec Package

The mathspec allows to use any OpenType font for mathmode (at the cost of bad spacing).

\documentclass{article}
\usepackage{mathspec}
\setmathfont(Latin,Digits,Greek){Latin Modern Sans}
\setmathrm{Latin Modern Sans}
\begin{document}
Lorem ipsum
\[ \sum_{k=0}^\infty a_0q^k = \lim_{n\to\infty}\sum_{k=0}^n a_0q^k =
            \lim_{n\to\infty} a_0\frac{1-q^{n+1}}{1-q} = \frac{a_0}{1-q} \]
dolor sit amet
\end{document}