How can I tell if the ANSYS sparse solver has used the pivoting option?
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Pivoting is a technique in which the solution of singular equations is postponed until the other equations have been solved, at which time it is less likely to be singular. We automatically turn on pivoting for certain problems - generally the U/P formulation elements and 17x elements. If bcsopt,,,,,,-5 is added there will be a message with the solver output that tells when the pivoting option is in use. The effect on performance ranges from next to nothing to a LOT, depending on whether pivoting actually happens. Turning it on just means we test for small diags and pivot when the test threshold is reached. Pivoting generally increases memory and op count but it is only significant when a lot of pivoting happens. I avoid it if possible and in some cases it is good to override our default of turning it on by using eqsolve,sparse,-1 |
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