https://blender.stackexchange.com/questions/44637/how-can-i-manually-calculate-bpy-types-posebone-matrix-using-blenders-python-ap/44975
The Quest to become a Stallmanite
https://blender.stackexchange.com/questions/44637/how-can-i-manually-calculate-bpy-types-posebone-matrix-using-blenders-python-ap/44975