Alternativ bietet Paket `physics` ein paar Annehmlichkeiten.
![vagueCreatureReynoldEquation][1]
\documentclass[border=10pt]{standalone}
\documentclass[math,border=10pt]{standalone}
\usepackage{mathtools}
\usepackage{physics}
\begin{document}
$\displaystyle
\[
\pderivative{\theta}(PH^{3} \pdv{P}{\theta})
+
+ \pdv{z}(PH^{3} \pdv{P}{z}) =
\lambda \pdv{\theta}(PH)
+ 2\lambda \cdot \nu \cdot \pdv{\tau}(PH)
$
\]
\end{document}
[1]: http://texwelt.de/wissen/upfiles/vagueCreatureReynoldEquation.png
