<p>It just means that both matrix arguments A and B are the same.</p>
<p>What happens if you use this direct solver as a preconditioner?</p>
<div class="gmail_quote">On May 17, 2012 2:23 PM, "Colin McAuliffe" <<a href="mailto:cjm2176@columbia.edu">cjm2176@columbia.edu</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hello!<br>
<br>
I am solving a coupled multiphysics problem which has several different units, which leads to a poorly conditioned jacobian. I am using the following ksp options:<br>
<br>
-ksp_type preonly -pc_type lu -pc_factor_mat_solver_package umfpack<br>
<br>
The results I am getting are not right and I suspect that the conditioning of the jacobian may be playing a part in that. I would like to improve the conditioning by using -ksp_diagonal_scale, but adding it does not seem to help. The documentation for this option says 'this routine is only used if the matrix and preconditioner matrix are the same thing'.<br>
<br>
Does that mean the command can only be used with no preconditioner?<br>
<br>
<a href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetDiagonalScale.html" target="_blank">http://www.mcs.anl.gov/petsc/<u></u>petsc-current/docs/<u></u>manualpages/KSP/<u></u>KSPSetDiagonalScale.html</a><br>
<br>
All the best,<br>
<br>
-- <br>
Colin McAuliffe<br>
PhD Candidate<br>
Columbia University<br>
Department of Civil Engineering and Engineering Mechanics<br>
</blockquote></div>