Can you use the debugger to get a stack trace?<br><br> Matt<br><br><div class="gmail_quote">On Tue, Nov 24, 2009 at 10:46 AM, francois pacull <span dir="ltr"><<a href="mailto:fpacull@fluorem.com">fpacull@fluorem.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Dear PETSc team,<br>
<br>
I am having a little bit of trouble with the Schur option of PCFieldSplit: I would like to apply some special treatments respectively to the five first and the two last equations over seven for each grid node of a CFD linear system...<br>
<br>
In the present case, the KSP is "gmres" (or "fgmres" if the PC is changing), the PC is "asm" (the subdomain IS is defined with PCASMSetLocalSubdomains in order to always include all the fields associated to the grid points of the overlap), the SUBKSP is "preonly" and the SUBPC is "fieldsplit".<br>
<br>
So far the FieldSplit options PC_COMPOSITE_ADDITIVE and PC_COMPOSITE_MULTIPLICATIVE work well with fieldsplit_0 and fieldsplit_1 set to KSPPREONLY and PCILU in the following way:<br>
<br>
PCFieldSplitGetSubKSP(SubPC,number_of_split,&FieldSplitKSP);<br>
... [for the fields 0,1,2,3,4 (fieldsplit_0)]<br>
KSPSetType(FieldSplitKSP[0],KSPPREONLY);<br>
KSPGetPC(FieldSplitKSP[0],&FieldSplitPC0);<br>
PCSetType(FieldSplitPC0,PCILU);<br>
... [for the fields 5 and 6 (fieldsplit_1)]<br>
KSPSetType(FieldSplitKSP[1],KSPPREONLY);<br>
KSPGetPC(FieldSplitKSP[1],&FieldSplitPC1);<br>
PCSetType(FieldSplitPC1,PCILU);<br>
...<br>
<br>
They also work well when I set the FieldSplitKSP[0] and/or FieldSplitKSP[1] to KSPGMRES. However, I always get a segmentation violation when I try to use the FieldSplit option PC_COMPOSITE_SCHUR... I guess that I am missing something: is there more options to set in this Schur case?<br>
So far I did not turn on the Schur complement preconditioner option: PCFieldSplitSchurPrecondition(subpc,PETSC_FALSE);<br>
Is there a book or article describing the methods implemented in this FieldSplit option?<br>
<br>
The version is petsc-3.0.0-p7...<br>
<br>
Thank you for your help,<br>
Regards,<br><font color="#888888">
francois pacull.<br>
<br>
</font></blockquote></div><br><br clear="all"><br>-- <br>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>-- Norbert Wiener<br>