[petsc-users] QCG and KSPSetPCSide

[hong at aspiritech.org]

PETSc implementation of qcg only allows symmetric preconditioner, which is
set in the code.
Hong

On Mon, Jun 29, 2015 at 9:54 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Mon, Jun 29, 2015 at 9:22 AM, <Carol.Brickley at awe.co.uk> wrote:
>
>> All,
>>
>> I am trying to use KSPSolve for a QCG solver using petsc 3.4.3 and it
>> gives me the error of "PC does not have left symmetric apply!". Further
>> reading on the web pages suggest I
>
>
> CG is the Krylov Solver (KSP), but the error message is about the
> Preconditioner (PC). QCG by default uses symmetric application, and by
> default the PC is ILU which does not have a symmetric apply. You can use
> -ksp_pc_side left
>
>   Thanks,
>
>      Matt
>
>
>> need to use KSPSetPCSide to set up a symmetric side for the solver.
>> However, this does not seem to work. I am doing the following in an F90
>> code:
>>
>> call KSPSetPCType(ksp_ptr%ksp, 'qcg', petsc_err)
>> call KSPSetPCSide(ksp_ptr%ksp, PC_SYMMETRIC, petsc_err)
>>
>> but I still get the same failure message when I call
>> KSPSolve(ksp_ptr%ksp..)  later on.
>>
>> Any ideas as to why this is not working?
>>
>> Carol
>>
>>
>>
>>
>>
>> Dr Carol Brickley
>> BSc,PhD,ARCS,DIC,MBCS
>>
>> Senior Software Engineer
>> Applied Computer Science
>> DS+T,
>> AWE
>> Aldermaston
>> Reading
>> Berkshire
>> RG7 4PR
>>
>> Direct: 0118 9855035
>>
>>
>>
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>
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
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> -- Norbert Wiener
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