LuaLaTeX + libertine... the issue of math font
Since you give the no-math
option, you have to help fontspec
:
\documentclass[]{scrbook}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathtools}
\usepackage[libertine]{newtxmath}
\usepackage[no-math]{fontspec}
\usepackage{libertine}
\DeclareSymbolFont{operators}{\encodingdefault}{\familydefault}{\mddefault}{n}
\DeclareMathAlphabet{\mathit}{\encodingdefault}{\familydefault}{\mddefault}{it}
\DeclareMathAlphabet{\mathbf}{\encodingdefault}{\familydefault}{\bfdefault}{n}
\begin{document}
\begin{equation}
\mathit{TRUC} = \frac{1}{10} \times \sum _{d=0.2}^{12.8} \frac{\pi \times d \times A_{d}}{E_{d}}
\end{equation}
$\mathbf{ABC}$
\end{document}
Otherwise you need to restore the standard math codes for the digits.
\documentclass[]{scrbook}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathtools}
\usepackage[libertine]{newtxmath}
\usepackage{fontspec}
\usepackage{libertine}
\AtBeginDocument{%
\DeclareMathSymbol{0}{\mathalpha}{operators}{`0}%
\DeclareMathSymbol{1}{\mathalpha}{operators}{`1}%
\DeclareMathSymbol{2}{\mathalpha}{operators}{`2}%
\DeclareMathSymbol{3}{\mathalpha}{operators}{`3}%
\DeclareMathSymbol{4}{\mathalpha}{operators}{`4}%
\DeclareMathSymbol{5}{\mathalpha}{operators}{`5}%
\DeclareMathSymbol{6}{\mathalpha}{operators}{`6}%
\DeclareMathSymbol{7}{\mathalpha}{operators}{`7}%
\DeclareMathSymbol{8}{\mathalpha}{operators}{`8}%
\DeclareMathSymbol{9}{\mathalpha}{operators}{`9}%
}
\begin{document}
\showthe\mathcode`1
\begin{equation}
\mathit{TRUC} = \frac{1}{10} \times \sum _{d=0.2}^{12.8} \frac{\pi \times d \times A_{d}}{E_{d}}
\end{equation}
$\mathbf{ABC}$
\end{document}