Getting sans-serif math only in sans-serif mode

Question

I know how to get sans-serif math for the whole document—that is easy. My question is how do I get sans-serif math only when I am in a sans-serif mode? I would like the math font to be serif normally, but change to sans serif when I use sans-serif mode, such as using \textsf or something else.

In my case, I am using tufte-latex's sfsidenotes option, which puts all the typesets all the side notes in the document in the sans-serif style.

Consider this MWE:

\documentclass[nobib, sfsidenotes]{tufte-handout}
\renewcommand{\sfdefault}{cmbr}

\begin{document}

Let \(f\) be a continuous\sidenote{Moreover, this can be true when \(f\) is bounded on \(R\), \(f\) is discontinuous on only finitely many smooth curves, and the iterated integrals exist.} function on the rectangular region \(R = \{ (x, y) \mid a \leq x \leq b, c \leq y \leq d\}\). Then \[ \iint_R dA f(x, y) = \int_a^b dx \int_c^d dy f(x, y) = \int_c^d dy \int_a^b dx f(x, y).\]

The side notes that results is:

Notice that the f and the R are in the default serif font, which I find ugly.

Answer 1

You want to declare a sans-serif math version, similar to \mathversion{bold} and \boldmath. Here is a MWE declaring sans (and bold sans) math versions in LuaLaTeX/XeLaTeX:

\documentclass{article}
\usepackage[paperwidth=10cm]{geometry} % Formatting for a MWE on TeX.SX
\usepackage{unicode-math}
\usepackage{microtype}

\defaultfontfeatures{Ligatures=TeX, Scale=MatchLowercase}
\setmainfont{KpRoman}
\setsansfont{KpSans}
\setmonofont{KpMono}
\setmathfont{KpMath-Regular.otf}
\setmathfont{KpMath-Bold.otf}[version=bold]
\setmathfont{KpMath-Sans.otf}[version=sans]
\setmathfont{KpMath-Sansbold.otf}[version=boldsans]

\newcommand\sansmath{\mathversion{sans}}
\newcommand\boldsansmath{\mathversion{boldsans}}

\begin{document}

\section*{\sffamily\bfseries\boldsansmath Integration on Rectangular Regions of 
\(\mathbb{R}^2\)}


Let \(f\) be a continuous function on the rectangular region \(R = \{ (x, y) \mid a \leq x \leq b, c \leq y \leq d\}\). Then
\begin{align*}
&\iint_R dA f(x, y) \\
= &\int_a^b dx \int_c^d dy f(x, y) \\
= &\int_c^d dy \int_a^b dx f(x, y)
\end{align*}

\sffamily\sansmath
Moreover, this can be true when \(f\) is bounded on \(R\), \(f\) is discontinuous on only finitely many smooth curves, and the iterated integrals exist.

\end{document}

You could substitute any other OpenType Math fonts,. If you intend to use this often, you probably want to define an environment that sets \sffamily\sansmath, or add these to the definitions of high-level commands such as \sidenote.

For PDFLaTeX, the exact commands would depend on which legacy sans-serif math font you use, but here is a MWE to set up the fonts from sansmathfonts in \mathversion{sans}:

\documentclass{article}
\usepackage{amsmath}
\usepackage[paperwidth=10cm]{geometry} % Formatting for a MWE on TeX.SX

\DeclareMathVersion{sans}
\SetSymbolFont{operators}{sans}{OT1}{xcmss}{m}{n}
\SetSymbolFont{letters}{sans}{OML}{cmssm}{m}{it}
\SetSymbolFont{symbols}{sans}{OMS}{cmsssy}{m}{n}
\SetSymbolFont{largesymbols}{sans}{OMX}{cmssex}{m}{n}

\DeclareMathVersion{sansbold}
\SetSymbolFont{operators}{sansbold}{OT1}{xcmss}{bx}{n}
\SetSymbolFont{letters}{sansbold}{OML}{cmssm}{bx}{it}
\SetSymbolFont{symbols}{sansbold}{OMS}{cmsssy}{m}{n} % No bold symbols for this font.
\SetSymbolFont{largesymbols}{sansbold}{OMX}{cmssex}{m}{n} % No bold symbols for this font.

\newcommand\sansmath{\mathversion{sans}}
\newcommand\sansboldmath{\mathversion{sansbold}}

\begin{document}

\section*{\sffamily\bfseries\sansboldmath Integration on a Rectangular Region \(R\)}


Let \(f\) be a continuous function on the rectangular region \(R = \{ (x, y) \mid a \leq x \leq b, c \leq y \leq d\}\). Then
\begin{align*}
&\iint_R dA f(x, y) \\
= &\int_a^b dx \int_c^d dy f(x, y) \\
= &\int_c^d dy \int_a^b dx f(x, y)
\end{align*}

\sffamily\sansmath
Moreover, this can be true when \(f\) is bounded on \(R\), \(f\) is discontinuous on only finitely many smooth curves, and the iterated integrals exist.

\end{document}