KSPSolveTranspose and PCFieldSplit

[Randall Mackie]

Barry,

Okay, I assume this means it will be done at some point in the near future?

I tried taking the transpose in my code, and then using KSPSolve, but then
I was getting error messages about zero pivots. I then added
-pc_shift_positive_definite and it ran, but it didn't seem to do any better
than KSPSolveTranspose, although I haven't been able to spend a lot of time
on that.

I'll just add another KSP in my code, one to use the fieldsplit PC for
the first problem, and then another one to just use ILU for the transpose
problem, at least until you get the patch for fieldsplit PC.

Thanks, Randy


Barry Smith wrote:
> 
> On Tue, 26 Sep 2006, Randall Mackie wrote:
> 
>> When I try to use KSPSolveTranspose with PCFieldSplit, I get the following
>> errors:
>>
>> [0]PETSC ERROR: PCApplyTranspose() line 483 in src/ksp/pc/interface/precon.c
>> [0]PETSC ERROR: No support for this operation for this object type!
>> [0]PETSC ERROR:  !
>> [0]PETSC ERROR: KSPInitialResidual() line 56 in src/ksp/ksp/interface/itres.c
>> [0]PETSC ERROR: KSPSolve_BCGS() line 41 in src/ksp/ksp/impls/bcgs/bcgs.c
>> [0]PETSC ERROR: KSPSolveTranspose() line 562 in src/ksp/ksp/interface/itfunc.c
>>
> 
>    This is just "lazyness", I hadn't implemented the apply transpose. 
> I've added it now to PETSc-dev; the problem is it cannot be made into an
> easy patch since it involves several nontrivial changes.
> 
>     
>> So then I thought in my code I would just take the transpose of A and call
>> KSPSolve, but then I get the following errors:
>>
>> [0]PETSC ERROR: MatGetSubMatrix_SeqAIJ() line 1686 in
>> src/mat/impls/aij/seq/aij.c
>> [0]PETSC ERROR: Nonconforming object sizes!
>> [0]PETSC ERROR: Cannot reuse matrix. wrong no of nonzeros!
>> [0]PETSC ERROR: MatGetSubMatrices_SeqAIJ() line 1799 in
>> src/mat/impls/aij/seq/aij.c
>> [0]PETSC ERROR: MatGetSubMatrices() line 4828 in src/mat/interface/matrix.c
>> [0]PETSC ERROR: MatGetSubMatrix() line 5438 in src/mat/interface/matrix.c
>> [0]PETSC ERROR: PCSetUp_FieldSplit() line 162 in
>> src/ksp/pc/impls/fieldsplit/fieldsplit.c
>> [0]PETSC ERROR: PCSetUp() line 798 in src/ksp/pc/interface/precon.c
>> [0]PETSC ERROR: KSPSetUp() line 234 in src/ksp/ksp/interface/itfunc.c
>> [0]PETSC ERROR: KSPSolve() line 334 in src/ksp/ksp/interface/itfunc.c
>>
>>
>     I'm guessing you used MAT_SAME_NONZERO_PATTERN? But the transpose won't have 
> the same nonzero pattern?
> 
> BTW: Did you find explicitly forming the transposes and solving worked better
> than just using KSPSolveTranspose()?
> 
>   Barry
> 
>> Is there some reason why the PCFIeildSplit is not compatible with
>> KSPSolveTranspose?
>>
>> I'm solving with the following options:
>>
>>
>>          -em_ksp_truemonitor \
>>          -em_ksp_type bcgs \
>>          -em_pc_type fieldsplit \
>>          -em_pc_fieldsplit_default \
>>          -em_pc_fieldsplit_type multiplicative \
>>          -em_fieldsplit_pc_type bjacobi \
>>          -em_fieldsplit_sub_pc_type ilu \
>>          -em_fieldsplit_sub_pc_factor_levels 4 \
>>          -em_fieldsplit_sub_pc_factor_fill 10 \
>>
>> Randy
>>
>>
> 

-- 
Randall Mackie
GSY-USA, Inc.
PMB# 643
2261 Market St.,
San Francisco, CA 94114-1600
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