[petsc-users] Understanding index sets for PCGASM
Matthew Knepley
knepley at gmail.com
Thu May 4 11:04:57 CDT 2023
On Thu, May 4, 2023 at 11:24 AM LEONARDO MUTTI <
leonardo.mutti01 at universitadipavia.it> wrote:
> Thank you for the help.
> Adding to my example:
>
>
> * call PCGASMSetSubdomains(pc,NSub, subdomains_IS, inflated_IS,ierr)
> call PCGASMDestroySubdomains(NSub,subdomains_IS,inflated_IS,ierr)*
> results in:
>
> * Error LNK2019 unresolved external symbol PCGASMDESTROYSUBDOMAINS
> referenced in function ... *
>
> * Error LNK2019 unresolved external symbol PCGASMSETSUBDOMAINS
> referenced in function ... *
> I'm not sure if the interfaces are missing or if I have a compilation
> problem.
>
I just want to make sure you really want GASM. It sounded like you might
able to do what you want just with ASM.
Can you tell me again what you want to do overall?
Thanks,
Matt
> Thank you again.
> Best,
> Leonardo
>
> Il giorno sab 29 apr 2023 alle ore 20:30 Barry Smith <bsmith at petsc.dev>
> ha scritto:
>
>>
>> Thank you for the test code. I have a fix in the branch
>> barry/2023-04-29/fix-pcasmcreatesubdomains2d
>> <https://gitlab.com/petsc/petsc/-/commits/barry/2023-04-29/fix-pcasmcreatesubdomains2d> with
>> merge request https://gitlab.com/petsc/petsc/-/merge_requests/6394
>>
>> The functions did not have proper Fortran stubs and interfaces so I
>> had to provide them manually in the new branch.
>>
>> Use
>>
>> git fetch
>> git checkout barry/2023-04-29/fix-pcasmcreatesubdomains2d
>> <https://gitlab.com/petsc/petsc/-/commits/barry/2023-04-29/fix-pcasmcreatesubdomains2d>
>> ./configure etc
>>
>> Your now working test code is in src/ksp/ksp/tests/ex71f.F90 I had to
>> change things slightly and I updated the error handling for the latest
>> version.
>>
>> Please let us know if you have any later questions.
>>
>> Barry
>>
>>
>>
>>
>> On Apr 28, 2023, at 12:07 PM, LEONARDO MUTTI <
>> leonardo.mutti01 at universitadipavia.it> wrote:
>>
>> Hello. I am having a hard time understanding the index sets to feed
>> PCGASMSetSubdomains, and I am working in Fortran (as a PETSc novice). To
>> get more intuition on how the IS objects behave I tried the following
>> minimal (non) working example, which should tile a 16x16 matrix into 16
>> square, non-overlapping submatrices:
>>
>> #include <petsc/finclude/petscmat.h>
>> #include <petsc/finclude/petscksp.h>
>> #include <petsc/finclude/petscpc.h>
>> USE petscmat
>> USE petscksp
>> USE petscpc
>>
>> Mat :: A
>> PetscInt :: M, NSubx, dof, overlap, NSub
>> INTEGER :: I,J
>> PetscErrorCode :: ierr
>> PetscScalar :: v
>> KSP :: ksp
>> PC :: pc
>> IS :: subdomains_IS, inflated_IS
>>
>> call PetscInitialize(PETSC_NULL_CHARACTER , ierr)
>>
>> !-----Create a dummy matrix
>> M = 16
>> call MatCreateAIJ(MPI_COMM_WORLD, PETSC_DECIDE, PETSC_DECIDE,
>> & M, M,
>> & PETSC_DEFAULT_INTEGER, PETSC_NULL_INTEGER,
>> & PETSC_DEFAULT_INTEGER, PETSC_NULL_INTEGER,
>> & A, ierr)
>>
>> DO I=1,M
>> DO J=1,M
>> v = I*J
>> CALL MatSetValue (A,I-1,J-1,v,
>> & INSERT_VALUES , ierr)
>> END DO
>> END DO
>>
>> call MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY , ierr)
>> call MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY , ierr)
>>
>> !-----Create KSP and PC
>> call KSPCreate(PETSC_COMM_WORLD,ksp, ierr)
>> call KSPSetOperators(ksp,A,A, ierr)
>> call KSPSetType(ksp,"bcgs",ierr)
>> call KSPGetPC(ksp,pc,ierr)
>> call KSPSetUp(ksp, ierr)
>> call PCSetType(pc,PCGASM, ierr)
>> call PCSetUp(pc , ierr)
>>
>> !-----GASM setup
>> NSubx = 4
>> dof = 1
>> overlap = 0
>>
>> call PCGASMCreateSubdomains2D(pc,
>> & M, M,
>> & NSubx, NSubx,
>> & dof, overlap,
>> & NSub, subdomains_IS, inflated_IS, ierr)
>>
>> call ISView(subdomains_IS, PETSC_VIEWER_STDOUT_WORLD, ierr)
>>
>> call KSPDestroy(ksp, ierr)
>> call PetscFinalize(ierr)
>>
>> Running this on one processor, I get NSub = 4.
>> If PCASM and PCASMCreateSubdomains2D are used instead, I get NSub = 16 as
>> expected.
>> Moreover, I get in the end "forrtl: severe (157): Program Exception -
>> access violation". So:
>> 1) why do I get two different results with ASM, and GASM?
>> 2) why do I get access violation and how can I solve this?
>> In fact, in C, subdomains_IS, inflated_IS should pointers to IS objects.
>> As I see on the Fortran interface, the arguments to
>> PCGASMCreateSubdomains2D are IS objects:
>>
>> subroutine PCGASMCreateSubdomains2D(a,b,c,d,e,f,g,h,i,j,z)
>> import tPC,tIS
>> PC a ! PC
>> PetscInt b ! PetscInt
>> PetscInt c ! PetscInt
>> PetscInt d ! PetscInt
>> PetscInt e ! PetscInt
>> PetscInt f ! PetscInt
>> PetscInt g ! PetscInt
>> PetscInt h ! PetscInt
>> IS i ! IS
>> IS j ! IS
>> PetscErrorCode z
>> end subroutine PCGASMCreateSubdomains2D
>> Thus:
>> 3) what should be inside e.g., subdomains_IS? I expect it to contain, for
>> every created subdomain, the list of rows and columns defining the subblock
>> in the matrix, am I right?
>>
>> Context: I have a block-tridiagonal system arising from space-time finite
>> elements, and I want to solve it with GMRES+PCGASM preconditioner, where
>> each overlapping submatrix is on the diagonal and of size 3x3 blocks (and
>> spanning multiple processes). This is PETSc 3.17.1 on Windows.
>>
>> Thanks in advance,
>> Leonardo
>>
>>
>>
--
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
https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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