Expanded the derivatives case to calculate Q (second invariant of grad(u,v,w)) and R (third invariant/determinant of grad(u,v,w)). These quantities are useful for detecting coherent structures in turbulent flows. To implement these changes the following files were created:
Additionally, the following files were modified (details in the commits):
I updated the version number to 2.1.6 (incrementing by 1 minor version), although this may be on the order of a patch ¯_(ツ)_/¯.