Erroneous results have been reported when using SpinDynamica v3.6.x with Mathematica version 13. This is very surprising behaviour since Mathematica should be backwards compatible. This has been pinned down to a surprising inconsistency in the handling of SparseArray objects between Mathematica versions 12 and 13. A bug report has been submitted to wolfram.com. SpinDynamica v3.7 …
