Consider the following code:
\font\rm=ecrm1000\rm
\font\bf=ecbx1000
R{\bf R} $R{\bf R}$
\bye
The result I get is RR RR.
However I was expecting RR RR
Why the second R in the math formula not rendered in bold?
Define a math bold font in Plain TeX
boldfontsplain-tex
Related Solutions
Separating out the font setting for math and text seems to work
\documentclass{article}
\usepackage{mathspec}
\setmainfont{Times New Roman}
\setmathfont{Times New Roman}
\begin{document}
\textbf{This line should all be bold: {\boldmath $17^2 = 289$}.}
\textbf{This line should all be bold except the
math: {$17^2 = 289$}.}
\end{document}
I don't get the error you claim, but some things go wrong, I believe because of how libertine interacts with mathspec.
One has to specify the classes for which Libertine is wanted, though, and this triggers the error about insufficient mathgroups. This can be cured with the method outlined in http://tex.stackexchange.com/a/100428/4427
This version works, by directly calling the fonts by name.
\documentclass{article}
\usepackage{etoolbox}
\makeatletter
%% http://tex.stackexchange.com/questions/100426/
%% http://tex.stackexchange.com/a/100428/
\def\new@mathgroup{\alloc@8\mathgroup\mathchardef\@cclvi}
\patchcmd{\document@select@group}{\sixt@@n}{\@cclvi}{}{}
\patchcmd{\select@group}{\sixt@@n}{\@cclvi}{}{}
\makeatother
\usepackage{amsthm}
\usepackage[libertine]{newtxmath}
\usepackage{mathspec,lipsum}
\setmainfont{Linux Libertine O}
\setmathsfont(Digits,Latin,Greek){Linux Libertine O}
\setmathrm{Linux Libertine O}
\setboldmathrm{Linux Libertine O}
\setmathsf{Linux Biolinum O}
\begin{document}
\lipsum[2]
\begin{gather}
\hat{Q}_i=\int_0^\infty \mathcal{G}^2(\mathbf{x})
\mathbf{\Sigma}^{-1}(x^2) f_i(x)\,dx=\mathsf{X} \\
\hat{Q}_i=\int_0^\infty \mathcal{G}^2(\mathbf{x})
\mathbf{\Sigma}^{-1}("x^2) f_i(x)\,dx=\mathsf{X}
\end{gather}
\end{document}
I added a line to your formula, showing how " is necessary as explained in the mathspec manual.
Best Answer
The selecting of text font has no effect in math typesetting. You defined
\bfas selecting text font only, you cannot expect anything in math.The plain TeX original
\bfmacro does two actions in parallel. See plain.tex file:First, it selects text font
\tenbfand second, it selects math alphabet collected in the\bffammath family by\fam\bffam.You can declare:
and keep the plain TeX macro
\bfunchanged. Now,\bfwill select your font in text mode and it keeps the selecting of math alphabet\fam\bffamin math mode.