[petsc-users] KSP changes for successive solver

Barry Smith bsmith at mcs.anl.gov
Thu Jul 16 17:30:04 CDT 2015


    This is a very annoying feature that has been fixed in master http://www.mcs.anl.gov/petsc/developers/index.html  I would like to have changed it in maint but Jed would have a shit-fit :-) since it changes behavior.


> On Jul 16, 2015, at 4:53 PM, Michele Rosso <mrosso at uci.edu> wrote:
> Hi,
> I am performing a series of solves inside a loop. The matrix for each solve changes but not enough to justify a rebuilt of the PC at each solve.
> Therefore I am using  KSPSetReusePreconditioner to avoid rebuilding unless necessary. The solver is CG + MG with a custom  PC at the coarse level.
> If KSP is not updated each time, everything works as it is supposed to. 
> When instead I allow the default PETSc  behavior, i.e. updating PC every time the matrix changes, the coarse level KSP , initially set to PREONLY, is changed into GMRES 
> after the first solve. I am not sure where the problem lies (my PC or PETSc), so I would like to have your opinion on this.
> I attached the ksp_view for the 2 successive solve and the options stack.
> Thanks for your help,
> Michel
> <ksp_view.txt><petsc_options.txt>

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