Limits set with \mathclap are invisible in final pdf

Question

I have a strange problem when typesetting sums, integrals etc. with long limits. Using the \mathclap command from mathtools, I want to type something like this

$ A = \int\limits_{\text{a very long limit that would look prettier with mathclap}}^\infty \mathrm{d} x x^2 $

(unfortunately mathclap isn't supported here it seems). However, anytime I try to use {\mathclap{...}}, like in this example

\documentclass[a4paper,10pt]{scrartcl} 

\usepackage{amssymb,amsmath}  
\usepackage[utf8]{inputenc}
\usepackage{mathtools}
\begin{document}

\[
\Delta \varphi = 2 \int_{\mathclap{0(\frac{b}{r} \to 0 as r \to \infty)}}^{w_1} d w \left( 1 - w^2 \left( 1 - \frac{2M}{b} w \right) \right)^{-\frac{1}{2}}
\]

\end{document}

all I get is something like this

No error codes or warnings are shown, it just doesn't render the lower limit, and I have no idea why. I'm using MiKTeX and TeXMaker on a Windows 10 machine. Normally I use pdfLaTeX to compile my .tex-files, but I've also tried XeLaTeX, to no avail.

Answer 1

this is more a comment than an answer, but it's too complicated for a comment.

i don't know why your lower limit is disappearing; i don't get that result. however, if you're going to use \mathclap, you almost certainly want to use \limits on this integral so that the lower limit doesn't overprint the integral sign. and the "as" is almost certainly text, not two variables multiplied with the "r".

finally, mathtools loads amsmath, so there's no reason to load both.

here's the result after those changes:

\documentclass[a4paper,10pt]{scrartcl} 

\usepackage{amssymb,mathtools}  
\usepackage[utf8]{inputenc}
\begin{document}

\[
\Delta \varphi =
 2 \int\limits_{\mathclap{0(\frac{b}{r} \to 0 \text{ as } r \to \infty)}}^{w_1} d w
 \left( 1 - w^2 \left( 1 - \frac{2M}{b} w \right) \right)^{-\frac{1}{2}}
\]

\end{document}