> On Sep 1, 2016, at 5:42 PM, Manuel Valera <[email protected]> wrote:
>
> Hello everyone,
>
> As my first intervention in this list i want to congratulate the PETSc devs,
> since ive been working with the library for a couple months and i am very
> impressed with it.
>
> Up until now, ive been developing a module to solve a big laplacian CSR
> matrix by multigrid pc and GCR ksp, i think i have a basic understanding of
> whats happening, but i cannot seem to find a good multigrid implementation
> for my case. I need to use some kind of automatic coarsener/interpolator and
> so far turning galerkin on does not seem to be working.
>
> The part of my code where i try to implement multigrid looks like this:
>
>
> call PCSetType(mg,PCJACOBI,ierr)
> call PCSetOperators(mg,pmat,pmat,ierr)
>
> !!trying to implement interpolators from ex42
> nl = 2
> call PetscMalloc(nl,da_list,ierr)
> da_list = PETSC_NULL_OBJECT
> call PetscMalloc(nl,daclist,ierr)
> daclist = PETSC_NULL_OBJECT
> ! ???? not sure what to do here...
>
>
> call PCMGSetLevels(mg,2,PETSC_NULL_OBJECT,ierr) !trying two levels first
> call PCMGSetType(mg,PC_MG_FULL,ierr)
> call PCMGSetGalerkin(mg,PETSC_TRUE,ierr)
>
> call PCMGSetCycleType(mg,PC_MG_CYCLE_V,ierr)
> call PCMGSetNumberSmoothDown(mg,1,ierr)
> call PCMGSetNumberSmoothUp(mg,1,ierr)
>
> call PCMGSetInterpolation(mg,1,pmat,ierr)
> call PCMGSetRestriction(mg,1,pmat,ierr)
> call PCMGSetX(mg,0,xp,ierr) !Probably and error to set these two
> call PCMGSetRhs(mg,0,bp,ierr)
>
> call PCSetUp(mg,ierr)
> ....
Don't do the above.
>
> I also have an alternative setup try, less developed as:
>
> call PCCreate(PETSC_COMM_WORLD,mg,ierr) !Create preconditioner context
> call PCSetType(mg,PCGAMG,ierr)
> call PCGAMGSetType(mg,PCGAMGAGG,ierr) !ERROR: 11 SEGV: Segmentation
> Violation | IS MY PETSC CORRUPTED? gamg.h empty
This should work ok. Send a complete file we can compile and run that
crashes like this.
> call PCGAMGSetNLevels(mg,3,PETSC_NULL_OBJECT,ierr)
> call PCGAMGSetNSmooths(mg,1,ierr)
> call PCGAMGSetThreshold(mg,0.0,ierr)
>
>
>
> So far i've also read ML/trilinos multigrid solver is probably easier to
> implement, but i cant seem to configure petsc correctly to download and
> install it
Use --download-ml with your ./configure command and send the resulting
configure.log to [email protected] if it does not work.
>
> From the code ive sent, can you spot any glaring errors? im sorry my
> knowledge of multigrid is very small.
>
> .-.-.-
>
> Finally, a second question,
>
> My CSR Column identifier (JA) array is not sorted for each row, can you give
> me an idea on how to sort it with PetscSortInt() for each row, as suggested
> in previous mails from this list?
>
> so far ive figured that i can loop over the row chunk using the spacing give
> by the row pointer array (IA) but i still don't know how to sort the row
> chunk in JA along with the real matrix values array (App).
PetscSortIntWithScalarArray()
>
> Any help will be apreciated,
>
> thanks so much,
>
> Manuel Valera.
> Computational Science Reseach Center - SDSU
>
>
>
>
>
