# Matplotlib compatibility patch for Pyodide
import matplotlib
if not hasattr(matplotlib.RcParams, "_get"):
    matplotlib.RcParams._get = dict.get

… for torsion in circular cross-sections and thin-walled tubes

The kinematic relation for torsion is defined by:

\[\chi = \frac{{{d}\varphi_x}}{{{d}x}}\]

This is treated in chapter 6.2.1 of the book Engineering Mechanics Volume 2 (Hartsuijker and Welleman, 2007).