LuaLaTeX + libertine... the issue of math font

Question

Would it be possible to use Libertine otf font (using LuaLaTeX and, for example, package libertine for automatic settings) for everything but in math mode where I'd like to use newtxmath and its libertine option (which produces acceptable output with pdfLaTeX)?

Neither :

\usepackage[libertine]{newtxmath}
\usepackage[no-math]{fontspec}
\usepackage{libertine}

nor

\usepackage[libertine]{newtxmath}
\usepackage[no-math]{fontspec}
\setmainfont[Ligatures={TeX}]{Linux Libertine O}

are successful. I get CM font for maths using the following:

%!TEX program = lualatex

\documentclass[]{scrbook}

\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathtools}

\usepackage[libertine]{newtxmath}
\usepackage[no-math]{fontspec}
\usepackage{libertine}

\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}

\end{document}

Answer 1

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}

Answer 2

Another approach is as follows, using the Linux Libertine system fonts, e.g., under lualatex:

\documentclass[]{scrbook}

\usepackage{luacode,luatexbase}
\usepackage{mathtools}
\usepackage{amssymb}

\usepackage[T1]{fontenc}
\usepackage[scaled=.85]{beramono}% used \mathtt; could use Libertine Mono
\usepackage[type1,scaled=.9]{cabin}% used \mathsf; could use Biolinum

\usepackage[libertine]{newtxmath}%

\usepackage{bm}% access to bold math; 

\providecommand\mathbfit[1]{\bm{\mathit #1}}% since unicode-math not loaded here.

\usepackage[no-math]{fontspec}
\setmainfont{Linux Libertine O} 
\setmonofont{Linux Libertine Mono O}[Scale=0.89]
\setsansfont{Linux Biolinum O}[Scale=MatchUppercase]


\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}

$\mathbf{ABC}$

$\mathbfit{ABC}$

\end{document}