Mike Rife
Ansys Employee

Hi greg2835

Ansys Inc has quite a few FEA programs, so it would help to know which you are asking about.  I will assume Mechanical APDL.  In the Ansys Help -> MAPDL there is a Theory Guide that should answer your questions.   Part of the difficulty in answering this is that it is assuming that there is only one FEA solver in MAPDL...there is not.