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.  

Mike