mathabx integral sign in newtxmath style

Question

I discovered that the Libertine font can be implemented in math mode using the newtxmath package. However, I prefer the integral sign from the mathabx package rather than the one contained in newtxmath. Is there any way to substitute only this one symbol? I'm using pdfLaTeX from TeX Live Manager on Windows 10.

P.S.: I'm not too much into the mechanics of TeX... so please try to keep your answer as simple as possible!

Answer 1

Copy some of the declarations from mathabx:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{libertine}
\usepackage[libertine]{newtxmath}
\usepackage{amsmath}

\DeclareFontFamily{U}{mathx}{\hyphenchar\font45}
\DeclareFontShape{U}{mathx}{m}{n}{<->mathx10}{}
\DeclareFontSubstitution{U}{mathx}{m}{n}
\DeclareSymbolFont{mathx}{U}{mathx}{m}{n}

\DeclareMathSymbol{\intop}  {\mathop}{mathx}{"B3}
\DeclareMathSymbol{\iintop} {\mathop}{mathx}{"B4}
\DeclareMathSymbol{\iiintop}{\mathop}{mathx}{"B5}
\DeclareMathSymbol{\ointop} {\mathop}{mathx}{"B6}
\DeclareMathSymbol{\oiintop}{\mathop}{mathx}{"B7}


\begin{document}

This is almost trivial to prove:
\begin{equation*}
\int_{-\infty}^{\infty}e^{-x^{2}}\,dx=\sqrt{\pi}
\end{equation*}
And here are the other integral symbols:
\begin{equation*}
\int\quad\iint\quad\iiint\quad\oint\quad\oiint
\end{equation*}

\end{document}

You may also want to try esint:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{libertine}
\usepackage[libertine]{newtxmath}
\usepackage{amsmath}
\usepackage{esint}

\begin{document}

This is almost trivial to prove:
\begin{equation*}
\int_{-\infty}^{\infty}e^{-x^{2}}\,dx=\sqrt{\pi}
\end{equation*}
And here are the other integral symbols:
\begin{equation*}
\int\quad\iint\quad\iiint\quad\oint\quad\oiint
\end{equation*}

\end{document}

A third possibility is to use the cmintegrals option:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{libertine}
\usepackage[libertine,cmintegrals]{newtxmath}
\usepackage{amsmath}

\begin{document}

This is almost trivial to prove:
\begin{equation*}
\int_{-\infty}^{\infty}e^{-x^{2}}\,dx=\sqrt{\pi}
\end{equation*}
And here are the other integral symbols:
\begin{equation*}
\int\quad\iint\quad\iiint\quad\oint
\end{equation*}

\end{document}