<div class="gmail_quote">On Fri, Jan 13, 2012 at 08:22, TAMAIN Patrick 207314 <span dir="ltr"><<a href="mailto:Patrick.TAMAIN@cea.fr">Patrick.TAMAIN@cea.fr</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<p class="MsoNormal"><font face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial">I somehow can’t figure out how to do this in practise with PETSC. I tried to configure the KSP like this<u></u><u></u></span></font></p>
<p class="MsoNormal"><font face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial">call KSPSetOperators(myKSP,A,B,SAME_PRECONDITIONER,ierr)
<u></u><u></u></span></font></p>
<p class="MsoNormal"><font face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial">and then run PETSC with the following options:<u></u><u></u></span></font></p>
<p class="MsoNormal"><font face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial">-pc_type asm -sub_pc_type lu -ksp_type bcgsl<u></u><u></u></span></font></p>
<p class="MsoNormal"><font face="Arial"><span lang="EN-GB" style="font-size:10.0pt;font-family:Arial">but the computation time becomes awful, far more than if I try to do separately the LU decomposition of the blocks of B with MUMPS.</span></font></p>
</blockquote></div><br><div>Make sure the subdomains are chosen to align with the direction you want to couple strongly (and perhaps span the domain if that is the method you want). There are APIs to set parallel subdomains that would couple on a subcommunicator.</div>
<div><br></div><div>I might consider using the original operator and just setting up the domain with this structure. The fill will be reasonably low if you have long, skinny domains.</div>