[petsc-dev] Problem in VecAXPY

[Matthew Knepley]

That cannot be right because this check was added two days ago.

   Matt

On Wed, Jun 16, 2010 at 10:40 AM, Lisandro Dalcin <dalcinl at gmail.com> wrote:

>
>
> On 16 June 2010 11:38, Matthew Knepley <knepley at gmail.com> wrote:
>
>> Barry,
>>
>>   You inserted a check in VecAXPY:563 (which Jed corrected)
>>
>>  jed at 16195<http://petsc/petsc-dev/annotate/c5b7ef1f9e2d/src/vec/vec/interface/rvector.c#l563>
>>
>>    563 <#129416afbe1f4061_1294132b5614bbcc_l563>
>>
>>   if (x == y) SETERRQ(((PetscObject)x)->comm,PETSC_ERR_ARG_IDN,"x and y cannot be the same vector");
>>
>>
>> However, this seems to make no sense in light of mg.c:53
>>
>>     ierr =
>> MatInterpolateAdd(mglevels->interpolate,mgc->x,mglevels->x,mglevels->x);CHKERRQ(ierr);
>>
>> which will eventually call this with y == w, and has stack
>>
>> 0]PETSC ERROR: VecAXPY() line 563 in src/vec/vec/interface/rvector.c
>> [0]PETSC ERROR: MatMultAdd_ML() line 179 in src/ksp/pc/impls/ml/ml.c
>> [0]PETSC ERROR: MatMultAdd() line 2041 in src/mat/interface/matrix.c
>> [0]PETSC ERROR: MatInterpolateAdd() line 6535 in
>> src/mat/interface/matrix.c
>> [0]PETSC ERROR: PCMGMCycle_Private() line 53 in src/ksp/pc/impls/mg/mg.c
>> [0]PETSC ERROR: PCMGMCycle_Private() line 50 in src/ksp/pc/impls/mg/mg.c
>> [0]PETSC ERROR: PCMGMCycle_Private() line 50 in src/ksp/pc/impls/mg/mg.c
>> [0]PETSC ERROR: PCApply_MG() line 288 in src/ksp/pc/impls/mg/mg.c
>> [0]PETSC ERROR: PCApply() line 358 in src/ksp/pc/interface/precon.c
>> [0]PETSC ERROR: KSPSolve_PREONLY() line 27 in
>> src/ksp/ksp/impls/preonly/preonly.c
>> [0]PETSC ERROR: KSPSolve() line 427 in src/ksp/ksp/interface/itfunc.c
>> [0]PETSC ERROR: PCApply_FieldSplit() line 530 in
>> src/ksp/pc/impls/fieldsplit/fieldsplit.c
>> [0]PETSC ERROR: PCApply() line 358 in src/ksp/pc/interface/precon.c
>> [0]PETSC ERROR: KSPInitialResidual() line 65 in
>> src/ksp/ksp/interface/itres.c
>> [0]PETSC ERROR: KSPSolve_GMRES() line 236 in
>> src/ksp/ksp/impls/gmres/gmres.c
>> [0]PETSC ERROR: KSPSolve() line 427 in src/ksp/ksp/interface/itfunc.c
>>
>> Can I remove this check?
>>
>>   Thanks,
>>
>>       Matt
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which their
>> experiments lead.
>> -- Norbert Wiener
>>
>
> I think x==y have to be special-cased (potential issues with arg aliasing
> in BLAS?). What about:  if (x==y) VecScale(x, 1+alpha)
>
> --
> Lisandro Dalcin
> ---------------
> CIMEC (INTEC/CONICET-UNL)
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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 experiments
lead.
-- Norbert Wiener
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