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How can one make the math mode change its font according to the surrounding text?

I have to use (pdf)latex. xelatex, luatex etc. are not possible alternatives in this case.

\documentclass{scrartcl}

\usepackage{lmodern}
%\usepackage{sfmath}
%\usepackage{cmbright}

\newcommand{\test}{%
    \sqrt{(a_1+a_2+\gamma)^2}=\sum_{i=1}^2 a_i + \gamma
}

\begin{document}
Text in roman family and math too $\test$
\begin{equation}
    \sqrt{(a_1+a_2+\gamma)^2}=\sum_{i=1}^2 a_i + \gamma
\end{equation}

\sffamily
Text in sans family and math should be in sans too $\test$
\begin{equation}
    \sqrt{(a_1+a_2+\gamma)^2}=\sum_{i=1}^2 a_i + \gamma
\end{equation}

\normalfont
Back to roman $\test$
\end{document}

I found sfmath but it only changes the latin letters and numbers and it works only as a global setting. cmbright contains a more or less matching (and working) math font but it changes the text font also and it works only globally too.

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1  
You should be aware that in math the font family can cary a meaning: a "A" in roman can be a different mathematical object than a "A" in typewriter. So you should be really careful when switching the math setup. In general adapting math "to the surroundig" text is not a good idea. –  Ulrike Fischer Oct 31 '11 at 10:45
    
@Ulrike: Hi, thanks for this advice. I’m familiar with this convention and support it in most cases. In this special case the formulas (mostly only one variable) are part of figures and graphics. The font inside all graphics has to be sans and it looks not good if the math text is in roman. I’ sure that there’ll be no confusion since the book deals only with simple math so that there is no differentiation between roman and serif necessary. I’ll ad an example to my question later this day. –  Tobi Oct 31 '11 at 14:35

2 Answers 2

If you use the Latin Modern or Computer Modern fonts, you can switch to CMBright:

\DeclareMathVersion{sans}
\SetSymbolFont{operators}{sans}{OT1}{cmbr}{m}{n}
\SetSymbolFont{letters}{sans}{OML}{cmbrm}{m}{it}
\SetSymbolFont{symbols}{sans}{OMS}{cmbrs}{m}{n}
\SetMathAlphabet{\mathit}{sans}{OT1}{cmbr}{m}{sl}
\SetMathAlphabet{\mathbf}{sans}{OT1}{cmbr}{bx}{n}
\SetMathAlphabet{\mathtt}{sans}{OT1}{cmtl}{m}{n}
\SetSymbolFont{largesymbols}{sans}{OMX}{iwona}{m}{n}

(and Iwona for the large symbols); then a declaration such as

\sffamily\mathversion{sans}

will do; it respects grouping, but also \normalfont\mathversion{normal} will get back to normal.

enter image description here

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Thank you very much! It seems to work perfectly :-) Could you explain how \DeclareMathVersion knows which of the settings belong to the serif version? –  Tobi Oct 31 '11 at 17:19
    
\DeclareMathVersion just sets up things so that it's possible to add math fonts to it with \Set... commands. It's a feature used normally for \mathversion{bold}. –  egreg Oct 31 '11 at 17:22
    
So every following \Set.. macros belong to the latest \DeclareMathVersion command? –  Tobi Oct 31 '11 at 17:32
    
@Tobi The math version is specified among the arguments of the \Set... commands. –  egreg Oct 31 '11 at 17:35
    
A moment ago I found it out my self … Thanks again! –  Tobi Oct 31 '11 at 17:48
up vote 7 down vote accepted

This is what I compiled form my own ideas and egreg’s answer to make the mathfont automatically change to sans and/or bold font.

\documentclass[parskip=half]{scrartcl}

\usepackage[T1]{fontenc}
\usepackage{lmodern}

\DeclareMathVersion{sans}
\SetSymbolFont{operators}{sans}{OT1}{cmbr}{m}{n}
\SetSymbolFont{letters}{sans}{OML}{cmbrm}{m}{it}
\SetSymbolFont{symbols}{sans}{OMS}{cmbrs}{m}{n}
\SetMathAlphabet{\mathit}{sans}{OT1}{cmbr}{m}{sl}
\SetMathAlphabet{\mathbf}{sans}{OT1}{cmbr}{bx}{n}
\SetMathAlphabet{\mathtt}{sans}{OT1}{cmtl}{m}{n}
\SetSymbolFont{largesymbols}{sans}{OMX}{iwona}{m}{n}

\DeclareMathVersion{boldsans}
\SetSymbolFont{operators}{boldsans}{OT1}{cmbr}{b}{n}
\SetSymbolFont{letters}{boldsans}{OML}{cmbrm}{b}{it}
\SetSymbolFont{symbols}{boldsans}{OMS}{cmbrs}{b}{n}
\SetMathAlphabet{\mathit}{boldsans}{OT1}{cmbr}{b}{sl}
\SetMathAlphabet{\mathbf}{boldsans}{OT1}{cmbr}{bx}{n}
\SetMathAlphabet{\mathtt}{boldsans}{OT1}{cmtl}{b}{n}
\SetSymbolFont{largesymbols}{boldsans}{OMX}{iwona}{bx}{n}

\newif\IfInSansMode
\let\oldsf\sffamily
\renewcommand*{\sffamily}{\oldsf\mathversion{sans}\InSansModetrue}
\let\oldmd\mdseries
\renewcommand*{\mdseries}{\oldmd\IfInSansMode\mathversion{sans}\fi\relax}
\let\oldbf\bfseries
\renewcommand*{\bfseries}{\oldbf\IfInSansMode\mathversion{boldsans}\else%
   \mathversion{bold}\fi\relax}
\let\oldnorm\normalfont
\renewcommand*{\normalfont}{\oldnorm\InSansModefalse\mathversion{normal}}
\let\oldrm\rmfamily
\renewcommand*{\rmfamily}{\oldrm\InSansModefalse\mathversion{normal}}

\usepackage[textwidth=9cm]{geometry}

\begin{document}
\section{Inline-$m\alpha \tau h$}
Normal: A $Ax\alpha+\chi b$

\sffamily Sans: A $Ax\alpha+\chi b$

\bfseries Bold-Sans: A $ Ax\alpha+\chi b$

\normalfont Normal: A $ Ax\alpha+\chi b$

\bfseries  Bold: A $ Ax\alpha+\chi b$

\normalfont Normal: A $ Ax\alpha+\chi b$

\section{Display-$\mu\alpha\tau\eta$}
Text in roman family
\begin{equation}
     \sqrt{(a_1+a_2+\gamma)^2}=\sum_{i=1}^2 a_i + \gamma
\end{equation}

\sffamily
Text in sans family
\begin{equation}
    \sqrt{(a_1+a_2+\gamma)^2}=\sum_{i=1}^2 a_i + \gamma
\end{equation}

\sffamily\bfseries
Text in sans family, bold version
\begin{equation}
    \sqrt{(a_1+a_2+\gamma)^2}=\sum_{i=1}^2 a_i + \gamma
\end{equation}

\rmfamily\bfseries
Text in roman family, bold version
\begin{equation}
    \sqrt{(a_1+a_2+\gamma)^2}=\sum_{i=1}^2 a_i + \gamma
\end{equation}
\end{document}

result

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