[petsc-users] Understanding index sets for PCGASM
Barry Smith
bsmith at petsc.dev
Wed May 17 21:26:20 CDT 2023
Yikes. Such huge numbers usually come from integer overflow or memory corruption.
The code to decide on the memory that needs allocating is straightforward
PetscErrorCode MatCreateSubMatrices_MPIAIJ(Mat C, PetscInt ismax, const IS isrow[], const IS iscol[], MatReuse scall, Mat *submat[])
{
PetscInt nmax, nstages = 0, i, pos, max_no, nrow, ncol, in[2], out[2];
PetscBool rowflag, colflag, wantallmatrix = PETSC_FALSE;
Mat_SeqAIJ *subc;
Mat_SubSppt *smat;
PetscFunctionBegin;
/* Check for special case: each processor has a single IS */
if (C->submat_singleis) { /* flag is set in PCSetUp_ASM() to skip MPI_Allreduce() */
PetscCall(MatCreateSubMatrices_MPIAIJ_SingleIS(C, ismax, isrow, iscol, scall, submat));
C->submat_singleis = PETSC_FALSE; /* resume its default value in case C will be used for non-single IS */
PetscFunctionReturn(PETSC_SUCCESS);
}
/* Collect global wantallmatrix and nstages */
if (!C->cmap->N) nmax = 20 * 1000000 / sizeof(PetscInt);
else nmax = 20 * 1000000 / (C->cmap->N * sizeof(PetscInt));
if (!nmax) nmax = 1;
if (scall == MAT_INITIAL_MATRIX) {
/* Collect global wantallmatrix and nstages */
if (ismax == 1 && C->rmap->N == C->cmap->N) {
PetscCall(ISIdentity(*isrow, &rowflag));
PetscCall(ISIdentity(*iscol, &colflag));
PetscCall(ISGetLocalSize(*isrow, &nrow));
PetscCall(ISGetLocalSize(*iscol, &ncol));
if (rowflag && colflag && nrow == C->rmap->N && ncol == C->cmap->N) {
wantallmatrix = PETSC_TRUE;
PetscCall(PetscOptionsGetBool(((PetscObject)C)->options, ((PetscObject)C)->prefix, "-use_fast_submatrix", &wantallmatrix, NULL));
}
}
/* Determine the number of stages through which submatrices are done
Each stage will extract nmax submatrices.
nmax is determined by the matrix column dimension.
If the original matrix has 20M columns, only one submatrix per stage is allowed, etc.
*/
nstages = ismax / nmax + ((ismax % nmax) ? 1 : 0); /* local nstages */
in[0] = -1 * (PetscInt)wantallmatrix;
in[1] = nstages;
PetscCall(MPIU_Allreduce(in, out, 2, MPIU_INT, MPI_MAX, PetscObjectComm((PetscObject)C)));
wantallmatrix = (PetscBool)(-out[0]);
nstages = out[1]; /* Make sure every processor loops through the global nstages */
} else { /* MAT_REUSE_MATRIX */
if (ismax) {
subc = (Mat_SeqAIJ *)(*submat)[0]->data;
smat = subc->submatis1;
} else { /* (*submat)[0] is a dummy matrix */
smat = (Mat_SubSppt *)(*submat)[0]->data;
}
if (!smat) {
/* smat is not generated by MatCreateSubMatrix_MPIAIJ_All(...,MAT_INITIAL_MATRIX,...) */
wantallmatrix = PETSC_TRUE;
} else if (smat->singleis) {
PetscCall(MatCreateSubMatrices_MPIAIJ_SingleIS(C, ismax, isrow, iscol, scall, submat));
PetscFunctionReturn(PETSC_SUCCESS);
} else {
nstages = smat->nstages;
}
}
if (wantallmatrix) {
PetscCall(MatCreateSubMatrix_MPIAIJ_All(C, MAT_GET_VALUES, scall, submat));
PetscFunctionReturn(PETSC_SUCCESS);
}
/* Allocate memory to hold all the submatrices and dummy submatrices */
if (scall == MAT_INITIAL_MATRIX) PetscCall(PetscCalloc1(ismax + nstages, submat));
for (i = 0, pos = 0; i < nstages; i++) {
if (pos + nmax <= ismax) max_no = nmax;
else if (pos >= ismax) max_no = 0;
else max_no = ismax - pos;
PetscCall(MatCreateSubMatrices_MPIAIJ_Local(C, max_no, isrow + pos, iscol + pos, scall, *submat + pos));
if (!max_no) {
if (scall == MAT_INITIAL_MATRIX) { /* submat[pos] is a dummy matrix */
smat = (Mat_SubSppt *)(*submat)[pos]->data;
smat->nstages = nstages;
}
pos++; /* advance to next dummy matrix if any */
} else pos += max_no;
}
if (ismax && scall == MAT_INITIAL_MATRIX) {
/* save nstages for reuse */
subc = (Mat_SeqAIJ *)(*submat)[0]->data;
smat = subc->submatis1;
smat->nstages = nstages;
}
PetscFunctionReturn(PETSC_SUCCESS);
}
The easiest way to debug would be to put a breakpoint in MatCreateSubMatrices_MPIAIJ on MPI rank zero and next through the subroutine to see where the crazy number appears that gets passed down in the line if (scall == MAT_INITIAL_MATRIX) PetscCall(PetscCalloc1(ismax + nstages, submat)); where either ismax or nstages has a crazy value.
If you are using the GNU compilers you can use the command line options -start_in_debugger noxterm -debugger_ranks 0 to start the Gnu debugger. If you are using the Microsoft Windows compilers you will need to use their debugger, I don't know how to do that (and shudder at the thought :-).
> On May 17, 2023, at 7:51 PM, Leonardo Mutti <leonardo.mutti01 at universitadipavia.it> wrote:
>
> Thanks for the reply. Even without Valgrind (which I can't use since I'm on Windows), by further simplifying the example, I was able to have PETSc display a more informative message.
> What I am doing wrong and what should be done differently, this is still unclear to me.
>
> The simplified code runs on 2 processors, I built a 4x4 matrix.
> The subdomains are now given by [0,1] and [2,3], with [2,3] inflating to [0,1,2,3].
>
> Thank you again.
>
> Error:
>
> [0]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
> [0]PETSC ERROR: Out of memory. This could be due to allocating
> [0]PETSC ERROR: too large an object or bleeding by not properly
> [0]PETSC ERROR: destroying unneeded objects.
> [0]PETSC ERROR: Memory allocated 0 Memory used by process 0
> [0]PETSC ERROR: Try running with -malloc_dump or -malloc_view for info.
> [0]PETSC ERROR: Memory requested 9437902811936987136
> [0]PETSC ERROR: WARNING! There are option(s) set that were not used! Could be the program crashed before they were used or a spelling mistake, etc!
> [0]PETSC ERROR: Option left: name:-pc_gasm_view_subdomains value: 1 source: code
> [0]PETSC ERROR: Option left: name:-sub_ksp_type value: gmres source: code
> [0]PETSC ERROR: Option left: name:-sub_pc_type value: none source: code
> [0]PETSC ERROR: See https://petsc.org/release/faq/ for trouble shooting.
> [0]PETSC ERROR: Petsc Development GIT revision: v3.19.1-234-g43977f8d16 GIT Date: 2023-05-08 14:50:03 +0000
> [...]
> [0]PETSC ERROR: #1 PetscMallocAlign() at ...\Sources\Git\Test-FV\PETSC-~1\src\sys\memory\mal.c:66
> [0]PETSC ERROR: #2 PetscMallocA() at ...\Sources\Git\Test-FV\PETSC-~1\src\sys\memory\mal.c:411
> [0]PETSC ERROR: #3 MatCreateSubMatrices_MPIAIJ() at ...\Sources\Git\Test-FV\PETSC-~1\src\mat\impls\aij\mpi\mpiov.c:2025
> [0]PETSC ERROR: #4 MatCreateSubMatricesMPI_MPIXAIJ() at ...\Sources\Git\Test-FV\PETSC-~1\src\mat\impls\aij\mpi\mpiov.c:3136
> [0]PETSC ERROR: #5 MatCreateSubMatricesMPI_MPIAIJ() at ...\Sources\Git\Test-FV\PETSC-~1\src\mat\impls\aij\mpi\mpiov.c:3208
> [0]PETSC ERROR: #6 MatCreateSubMatricesMPI() at ...\Sources\Git\Test-FV\PETSC-~1\src\mat\INTERF~1\matrix.c:7071
> [0]PETSC ERROR: #7 PCSetUp_GASM() at ...\Sources\Git\Test-FV\PETSC-~1\src\ksp\pc\impls\gasm\gasm.c:556
> [0]PETSC ERROR: #8 PCSetUp() at ...\Sources\Git\Test-FV\PETSC-~1\src\ksp\pc\INTERF~1\precon.c:994
> [0]PETSC ERROR: #9 KSPSetUp() at ...\Sources\Git\Test-FV\PETSC-~1\src\ksp\ksp\INTERF~1\itfunc.c:406
>
> Code, the important bit is after ! GASM, SETTING SUBDOMAINS:
>
> Mat :: A
> Vec :: b
> PetscInt :: M,N_blocks,block_size,NSub,I
> PetscErrorCode :: ierr
> PetscScalar :: v
> KSP :: ksp
> PC :: pc
> IS :: subdomains_IS(2), inflated_IS(2)
> PetscInt :: NMPI,MYRANK,IERMPI
> INTEGER :: start
>
> call PetscInitialize(PETSC_NULL_CHARACTER, ierr)
> call PetscLogDefaultBegin(ierr)
> call MPI_COMM_SIZE(MPI_COMM_WORLD, NMPI, IERMPI)
> CALL MPI_COMM_RANK(MPI_COMM_WORLD, MYRANK,IERMPI)
>
> N_blocks = 2
> block_size = 2
> M = N_blocks * block_size
>
>
> ! INTRO: create matrix and right hand side, create IS
>
> call MatCreateAIJ(PETSC_COMM_WORLD, PETSC_DECIDE, PETSC_DECIDE,
> & M, M, PETSC_DEFAULT_INTEGER, PETSC_NULL_INTEGER,
> & PETSC_DEFAULT_INTEGER, PETSC_NULL_INTEGER,A, ierr)
> call VecCreate(PETSC_COMM_WORLD,b,ierr)
> call VecSetSizes(b, PETSC_DECIDE, M,ierr)
> call VecSetFromOptions(b,ierr)
>
> DO I=(MYRANK*(M/NMPI)),((MYRANK+1)*(M/NMPI)-1)
>
> ! Set matrix
> v=1
> call MatSetValue(A, I, I, v, INSERT_VALUES, ierr)
> IF (I-block_size .GE. 0) THEN
> v=-1
> call MatSetValue(A, I, I-block_size, v, INSERT_VALUES, ierr)
> ENDIF
> ! Set rhs
> v = I
> call VecSetValue(b,I,v, INSERT_VALUES,ierr)
>
> END DO
>
> call MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY, ierr)
> call MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY, ierr)
> call VecAssemblyBegin(b,ierr)
> call VecAssemblyEnd(b,ierr)
>
> ! FIRST KSP/PC SETUP
>
> call KSPCreate(PETSC_COMM_WORLD, ksp, ierr)
> call KSPSetOperators(ksp, A, A, ierr)
> call KSPSetType(ksp, 'preonly', ierr)
> call KSPGetPC(ksp, pc, ierr)
> call PCSetType(pc, PCGASM, ierr)
>
>
> ! GASM, SETTING SUBDOMAINS
>
> if (myrank == 0) then
> call ISCreateStride(PETSC_COMM_SELF, 2, 0, 1, subdomains_IS(1), ierr)
> call ISCreateStride(PETSC_COMM_WORLD, 0, 0, 1, subdomains_IS(2), ierr)
> call ISCreateStride(PETSC_COMM_SELF, 2, 0, 1, inflated_IS(1), ierr)
> call ISCreateStride(PETSC_COMM_WORLD, 2, 0, 1, inflated_IS(2), ierr)
> start = 1
> NSub = 2
> else
> call ISCreateStride(PETSC_COMM_WORLD, 2, 2, 1, subdomains_IS(2), ierr)
> call ISCreateStride(PETSC_COMM_WORLD, 2, 2, 1, inflated_IS(2), ierr)
> start = 2
> NSub = 1
> endif
>
> call PCGASMSetSubdomains(pc,NSub,subdomains_IS(start:2),inflated_IS(start:2),ierr)
> call PCGASMDestroySubdomains(NSub,subdomains_IS(start:2),inflated_IS(start:2),ierr)
>
> ! GASM: SET SUBSOLVERS
>
> call PetscOptionsSetValue(PETSC_NULL_OPTIONS,"-sub_ksp_type", "gmres", ierr)
> call PetscOptionsSetValue(PETSC_NULL_OPTIONS,"-sub_pc_type", "none", ierr)
> call PetscOptionsSetValue(PETSC_NULL_OPTIONS,"-pc_gasm_view_subdomains", "1", ierr)
>
> call KSPSetUp(ksp, ierr)
> call PCSetUp(pc, ierr)
> call KSPSetFromOptions(ksp, ierr)
> call PCSetFromOptions(pc, ierr)
> call KSPView(ksp,PETSC_VIEWER_STDOUT_WORLD, ierr)
>
> call MatDestroy(A, ierr)
> call PetscFinalize(ierr)
>
>
> Il giorno mer 17 mag 2023 alle ore 21:55 Barry Smith <bsmith at petsc.dev <mailto:bsmith at petsc.dev>> ha scritto:
>>
>>
>>> On May 17, 2023, at 11:10 AM, Leonardo Mutti <leonardo.mutti01 at universitadipavia.it <mailto:leonardo.mutti01 at universitadipavia.it>> wrote:
>>>
>>> Dear developers, let me kindly ask for your help again.
>>> In the following snippet, a bi-diagonal matrix A is set up. It measures 8x8 blocks, each block is 2x2 elements. I would like to create the correct IS objects for PCGASM.
>>> The non-overlapping IS should be: [0,1], [2,3],[4,5], ..., [14,15]. The overlapping IS should be: [0,1], [0,1,2,3], [2,3,4,5], ..., [12,13,14,15]
>>> I am running the code with 4 processors. For some reason, after calling PCGASMDestroySubdomains the code crashes with severe (157): Program Exception - access violation. A visual inspection of the indices using ISView looks good.
>>
>> Likely memory corruption or use of an object or an array that was already freed. Best to use Valgrind to find the exact location of the mess.
>>
>>
>>> Thanks again,
>>> Leonardo
>>>
>>> Mat :: A
>>> Vec :: b
>>> PetscInt :: M,N_blocks,block_size,I,J,NSub,converged_reason,srank,erank,color,subcomm
>>> PetscMPIInt :: size
>>> PetscErrorCode :: ierr
>>> PetscScalar :: v
>>> KSP :: ksp
>>> PC :: pc
>>> IS,ALLOCATABLE :: subdomains_IS(:), inflated_IS(:)
>>> PetscInt :: NMPI,MYRANK,IERMPI
>>> INTEGER :: IS_counter, is_start, is_end
>>>
>>> call PetscInitialize(PETSC_NULL_CHARACTER, ierr)
>>> call PetscLogDefaultBegin(ierr)
>>> call MPI_COMM_SIZE(MPI_COMM_WORLD, NMPI, IERMPI)
>>> CALL MPI_COMM_RANK(MPI_COMM_WORLD, MYRANK,IERMPI)
>>>
>>> N_blocks = 8
>>> block_size = 2
>>> M = N_blocks * block_size
>>>
>>> ALLOCATE(subdomains_IS(N_blocks))
>>> ALLOCATE(inflated_IS(N_blocks))
>>>
>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>> ! ASSUMPTION: no block spans more than one rank (the inflated blocks can)
>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>
>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>> ! INTRO: create matrix and right hand side
>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>
>>> ! How many inflated blocks span more than one rank? NMPI-1 !
>>>
>>> call MatCreateAIJ(PETSC_COMM_WORLD, PETSC_DECIDE, PETSC_DECIDE,
>>> & M, M, PETSC_DEFAULT_INTEGER, PETSC_NULL_INTEGER,
>>> & PETSC_DEFAULT_INTEGER, PETSC_NULL_INTEGER,A, ierr)
>>> call VecCreate(PETSC_COMM_WORLD,b,ierr)
>>> call VecSetSizes(b, PETSC_DECIDE, M,ierr)
>>> call VecSetFromOptions(b,ierr)
>>>
>>> DO I=(MYRANK*(M/NMPI)),((MYRANK+1)*(M/NMPI)-1)
>>>
>>> ! Set matrix
>>> v=1
>>> call MatSetValue(A, I, I, v, INSERT_VALUES, ierr)
>>> IF (I-block_size .GE. 0) THEN
>>> v=-1
>>> call MatSetValue(A, I, I-block_size, v, INSERT_VALUES, ierr)
>>> ENDIF
>>> ! Set rhs
>>> v = I
>>> call VecSetValue(b,I,v, INSERT_VALUES,ierr)
>>>
>>> END DO
>>>
>>> call MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY, ierr)
>>> call MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY, ierr)
>>> call VecAssemblyBegin(b,ierr)
>>> call VecAssemblyEnd(b,ierr)
>>>
>>>
>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>> ! FIRST KSP/PC SETUP
>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>
>>> call KSPCreate(PETSC_COMM_WORLD, ksp, ierr)
>>> call KSPSetOperators(ksp, A, A, ierr)
>>> call KSPSetType(ksp, 'preonly', ierr)
>>> call KSPGetPC(ksp, pc, ierr)
>>> call PCSetType(pc, PCGASM, ierr)
>>>
>>>
>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>> !! GASM, SETTING SUBDOMAINS
>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>
>>> DO IS_COUNTER=1,N_blocks
>>>
>>> srank = MAX(((IS_COUNTER-2)*block_size)/(M/NMPI),0) ! start rank reached by inflated block
>>> erank = MIN(((IS_COUNTER-1)*block_size)/(M/NMPI),NMPI-1) ! end rank reached by inflated block. Coincides with rank containing non-inflated block
>>>
>>> ! Create subcomms
>>> color = MPI_UNDEFINED
>>> IF (myrank == srank .or. myrank == erank) THEN
>>> color = 1
>>> ENDIF
>>> call MPI_Comm_split(MPI_COMM_WORLD,color,MYRANK,subcomm,ierr)
>>>
>>> ! Create IS
>>> IF (srank .EQ. erank) THEN ! Block and overlap are on the same rank
>>> IF (MYRANK .EQ. srank) THEN
>>> call ISCreateStride(PETSC_COMM_SELF,block_size,(IS_COUNTER-1)*block_size,1,subdomains_IS(IS_COUNTER),ierr)
>>> IF (IS_COUNTER .EQ. 1) THEN ! the first block is not inflated
>>> call ISCreateStride(PETSC_COMM_SELF,block_size,(IS_COUNTER-1)*block_size,1,inflated_IS(IS_COUNTER),ierr)
>>> ELSE
>>> call ISCreateStride(PETSC_COMM_SELF,2*block_size,(IS_COUNTER-2)*block_size,1,inflated_IS(IS_COUNTER),ierr)
>>> ENDIF
>>> ENDIF
>>> else ! Block and overlap not on the same rank
>>> if (myrank == erank) then ! the block
>>> call ISCreateStride(subcomm,block_size,(IS_COUNTER-1)*block_size,1,subdomains_IS(IS_COUNTER),ierr)
>>> call ISCreateStride(subcomm,block_size,(IS_COUNTER-1)*block_size,1,inflated_IS(IS_COUNTER),ierr)
>>> endif
>>> if (myrank == srank) then ! the overlap
>>> call ISCreateStride(subcomm,block_size,(IS_COUNTER-2)*block_size,1,inflated_IS(IS_COUNTER),ierr)
>>> call ISCreateStride(subcomm,0,(IS_COUNTER-1)*block_size,1,subdomains_IS(IS_COUNTER),ierr)
>>> endif
>>> endif
>>>
>>> call MPI_Comm_free(subcomm, ierr)
>>> END DO
>>>
>>> ! Set the domains/subdomains
>>> NSub = N_blocks/NMPI
>>> is_start = 1 + myrank * NSub
>>> is_end = min(is_start + NSub, N_blocks)
>>> if (myrank + 1 < NMPI) then
>>> NSub = NSub + 1
>>> endif
>>>
>>> call PCGASMSetSubdomains(pc,NSub,subdomains_IS(is_start:is_end),inflated_IS(is_start:is_end),ierr)
>>> call PCGASMDestroySubdomains(NSub,subdomains_IS(is_start:is_end),inflated_IS(is_start:is_end),ierr)
>>>
>>> call PetscOptionsSetValue(PETSC_NULL_OPTIONS,"-sub_ksp_type", "gmres", ierr)
>>> call PetscOptionsSetValue(PETSC_NULL_OPTIONS,"-sub_pc_type", "none", ierr)
>>> call PetscOptionsSetValue(PETSC_NULL_OPTIONS,"-pc_gasm_view_subdomains", "1", ierr)
>>>
>>> call KSPSetUp(ksp, ierr)
>>> call PCSetUp(pc, ierr)
>>> call KSPSetFromOptions(ksp, ierr)
>>> call PCSetFromOptions(pc, ierr)
>>>
>>> call KSPView(ksp,PETSC_VIEWER_STDOUT_WORLD, ierr)
>>>
>>>
>>> Il giorno mer 10 mag 2023 alle ore 03:02 Barry Smith <bsmith at petsc.dev <mailto:bsmith at petsc.dev>> ha scritto:
>>>>
>>>>
>>>>> On May 9, 2023, at 4:58 PM, LEONARDO MUTTI <leonardo.mutti01 at universitadipavia.it <mailto:leonardo.mutti01 at universitadipavia.it>> wrote:
>>>>>
>>>>> In my notation diag(1,1) means a diagonal 2x2 matrix with 1,1 on the diagonal, submatrix in the 8x8 diagonal matrix diag(1,1,2,2,...,2).
>>>>> Am I then correct that the IS representing diag(1,1) is 0,1, and that diag(2,2,...,2) is represented by 2,3,4,5,6,7?
>>>>
>>>> I believe so
>>>>
>>>>> Thanks,
>>>>> Leonardo
>>>>>
>>>>> Il mar 9 mag 2023, 20:45 Barry Smith <bsmith at petsc.dev <mailto:bsmith at petsc.dev>> ha scritto:
>>>>>>
>>>>>> It is simplier than you are making it out to be. Each IS[] is a list of rows (and columns) in the sub (domain) matrix. In your case with the matrix of 144 by 144 the indices will go from 0 to 143.
>>>>>>
>>>>>> In your simple Fortran code you have a completely different problem. A matrix with 8 rows and columns. In that case if you want the first IS to represent just the first row (and column) in the matrix then it should contain only 0. The second submatrix which is all rows (but the first) should have 1,2,3,4,5,6,7
>>>>>>
>>>>>> I do not understand why your code has
>>>>>>
>>>>>>>>>> indices_first_domain = [0,1,8,9] ! corresponds to diag(1,1)
>>>>>>
>>>>>> it should just be 0
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>> On May 9, 2023, at 12:44 PM, LEONARDO MUTTI <leonardo.mutti01 at universitadipavia.it <mailto:leonardo.mutti01 at universitadipavia.it>> wrote:
>>>>>>>
>>>>>>> Partial typo: I expect 9x(16+16) numbers to be stored in subdomain_IS : # subdomains x (row indices of the submatrix + col indices of the submatrix).
>>>>>>>
>>>>>>> Il giorno mar 9 mag 2023 alle ore 18:31 LEONARDO MUTTI <leonardo.mutti01 at universitadipavia.it <mailto:leonardo.mutti01 at universitadipavia.it>> ha scritto:
>>>>>>>>
>>>>>>>>
>>>>>>>> ---------- Forwarded message ---------
>>>>>>>> Da: LEONARDO MUTTI <leonardo.mutti01 at universitadipavia.it <mailto:leonardo.mutti01 at universitadipavia.it>>
>>>>>>>> Date: mar 9 mag 2023 alle ore 18:29
>>>>>>>> Subject: Re: [petsc-users] Understanding index sets for PCGASM
>>>>>>>> To: Matthew Knepley <knepley at gmail.com <mailto:knepley at gmail.com>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Thank you for your answer, but I am still confused, sorry.
>>>>>>>> Consider https://gitlab.com/petsc/petsc/-/blob/main/src/ksp/ksp/tests/ex71f.F90 on one processor.
>>>>>>>> Let M=12 for the sake of simplicity, i.e. we deal with a 12x12 2D grid, hence, a 144x144 matrix.
>>>>>>>> Let NSubx = 3, so that on the grid we do 3 vertical and 3 horizontal subdivisions.
>>>>>>>> We should obtain 9 subdomains that are grids of 4x4 nodes each, thus corresponding to 9 submatrices of size 16x16.
>>>>>>>> In my run I obtain NSub = 9 (great) and subdomain_IS(i), i=1,...,9, reads:
>>>>>>>>
>>>>>>>> IS Object: 1 MPI process
>>>>>>>> type: general
>>>>>>>> Number of indices in set 16
>>>>>>>> 0 0
>>>>>>>> 1 1
>>>>>>>> 2 2
>>>>>>>> 3 3
>>>>>>>> 4 12
>>>>>>>> 5 13
>>>>>>>> 6 14
>>>>>>>> 7 15
>>>>>>>> 8 24
>>>>>>>> 9 25
>>>>>>>> 10 26
>>>>>>>> 11 27
>>>>>>>> 12 36
>>>>>>>> 13 37
>>>>>>>> 14 38
>>>>>>>> 15 39
>>>>>>>> IS Object: 1 MPI process
>>>>>>>> type: general
>>>>>>>> Number of indices in set 16
>>>>>>>> 0 4
>>>>>>>> 1 5
>>>>>>>> 2 6
>>>>>>>> 3 7
>>>>>>>> 4 16
>>>>>>>> 5 17
>>>>>>>> 6 18
>>>>>>>> 7 19
>>>>>>>> 8 28
>>>>>>>> 9 29
>>>>>>>> 10 30
>>>>>>>> 11 31
>>>>>>>> 12 40
>>>>>>>> 13 41
>>>>>>>> 14 42
>>>>>>>> 15 43
>>>>>>>> IS Object: 1 MPI process
>>>>>>>> type: general
>>>>>>>> Number of indices in set 16
>>>>>>>> 0 8
>>>>>>>> 1 9
>>>>>>>> 2 10
>>>>>>>> 3 11
>>>>>>>> 4 20
>>>>>>>> 5 21
>>>>>>>> 6 22
>>>>>>>> 7 23
>>>>>>>> 8 32
>>>>>>>> 9 33
>>>>>>>> 10 34
>>>>>>>> 11 35
>>>>>>>> 12 44
>>>>>>>> 13 45
>>>>>>>> 14 46
>>>>>>>> 15 47
>>>>>>>> IS Object: 1 MPI process
>>>>>>>> type: general
>>>>>>>> Number of indices in set 16
>>>>>>>> 0 48
>>>>>>>> 1 49
>>>>>>>> 2 50
>>>>>>>> 3 51
>>>>>>>> 4 60
>>>>>>>> 5 61
>>>>>>>> 6 62
>>>>>>>> 7 63
>>>>>>>> 8 72
>>>>>>>> 9 73
>>>>>>>> 10 74
>>>>>>>> 11 75
>>>>>>>> 12 84
>>>>>>>> 13 85
>>>>>>>> 14 86
>>>>>>>> 15 87
>>>>>>>> IS Object: 1 MPI process
>>>>>>>> type: general
>>>>>>>> Number of indices in set 16
>>>>>>>> 0 52
>>>>>>>> 1 53
>>>>>>>> 2 54
>>>>>>>> 3 55
>>>>>>>> 4 64
>>>>>>>> 5 65
>>>>>>>> 6 66
>>>>>>>> 7 67
>>>>>>>> 8 76
>>>>>>>> 9 77
>>>>>>>> 10 78
>>>>>>>> 11 79
>>>>>>>> 12 88
>>>>>>>> 13 89
>>>>>>>> 14 90
>>>>>>>> 15 91
>>>>>>>> IS Object: 1 MPI process
>>>>>>>> type: general
>>>>>>>> Number of indices in set 16
>>>>>>>> 0 56
>>>>>>>> 1 57
>>>>>>>> 2 58
>>>>>>>> 3 59
>>>>>>>> 4 68
>>>>>>>> 5 69
>>>>>>>> 6 70
>>>>>>>> 7 71
>>>>>>>> 8 80
>>>>>>>> 9 81
>>>>>>>> 10 82
>>>>>>>> 11 83
>>>>>>>> 12 92
>>>>>>>> 13 93
>>>>>>>> 14 94
>>>>>>>> 15 95
>>>>>>>> IS Object: 1 MPI process
>>>>>>>> type: general
>>>>>>>> Number of indices in set 16
>>>>>>>> 0 96
>>>>>>>> 1 97
>>>>>>>> 2 98
>>>>>>>> 3 99
>>>>>>>> 4 108
>>>>>>>> 5 109
>>>>>>>> 6 110
>>>>>>>> 7 111
>>>>>>>> 8 120
>>>>>>>> 9 121
>>>>>>>> 10 122
>>>>>>>> 11 123
>>>>>>>> 12 132
>>>>>>>> 13 133
>>>>>>>> 14 134
>>>>>>>> 15 135
>>>>>>>> IS Object: 1 MPI process
>>>>>>>> type: general
>>>>>>>> Number of indices in set 16
>>>>>>>> 0 100
>>>>>>>> 1 101
>>>>>>>> 2 102
>>>>>>>> 3 103
>>>>>>>> 4 112
>>>>>>>> 5 113
>>>>>>>> 6 114
>>>>>>>> 7 115
>>>>>>>> 8 124
>>>>>>>> 9 125
>>>>>>>> 10 126
>>>>>>>> 11 127
>>>>>>>> 12 136
>>>>>>>> 13 137
>>>>>>>> 14 138
>>>>>>>> 15 139
>>>>>>>> IS Object: 1 MPI process
>>>>>>>> type: general
>>>>>>>> Number of indices in set 16
>>>>>>>> 0 104
>>>>>>>> 1 105
>>>>>>>> 2 106
>>>>>>>> 3 107
>>>>>>>> 4 116
>>>>>>>> 5 117
>>>>>>>> 6 118
>>>>>>>> 7 119
>>>>>>>> 8 128
>>>>>>>> 9 129
>>>>>>>> 10 130
>>>>>>>> 11 131
>>>>>>>> 12 140
>>>>>>>> 13 141
>>>>>>>> 14 142
>>>>>>>> 15 143
>>>>>>>>
>>>>>>>> As you said, no number here reaches 144.
>>>>>>>> But the number stored in subdomain_IS are 9x16= #subdomains x 16, whereas I would expect, also given your latest reply, 9x16x16x2=#subdomains x submatrix height x submatrix width x length of a (row,column) pair.
>>>>>>>> It would really help me if you could briefly explain how the output above encodes the subdivision into subdomains.
>>>>>>>> Many thanks again,
>>>>>>>> Leonardo
>>>>>>>>
>>>>>>>>
>>>>>>>> Il giorno mar 9 mag 2023 alle ore 16:24 Matthew Knepley <knepley at gmail.com <mailto:knepley at gmail.com>> ha scritto:
>>>>>>>>> On Tue, May 9, 2023 at 10:05 AM LEONARDO MUTTI <leonardo.mutti01 at universitadipavia.it <mailto:leonardo.mutti01 at universitadipavia.it>> wrote:
>>>>>>>>>> Great thanks! I can now successfully run https://gitlab.com/petsc/petsc/-/blob/main/src/ksp/ksp/tests/ex71f.F90.
>>>>>>>>>>
>>>>>>>>>> Going forward with my experiments, let me post a new code snippet (very similar to ex71f.F90) that I cannot get to work, probably I must be setting up the IS objects incorrectly.
>>>>>>>>>>
>>>>>>>>>> I have an 8x8 matrix A=diag(1,1,2,2,...,2) and a vector b=(0.5,...,0.5). We have only one processor, and I want to solve Ax=b using GASM. In particular, KSP is set to preonly, GASM is the preconditioner and it uses on each submatrix an lu direct solver (sub_ksp = preonly, sub_pc = lu).
>>>>>>>>>>
>>>>>>>>>> For the GASM algorithm, I divide A into diag(1,1) and diag(2,2,...,2). For simplicity I set 0 overlap. Now I want to use GASM to solve Ax=b. The code follows.
>>>>>>>>>>
>>>>>>>>>> #include <petsc/finclude/petscmat.h>
>>>>>>>>>> #include <petsc/finclude/petscksp.h>
>>>>>>>>>> #include <petsc/finclude/petscpc.h>
>>>>>>>>>> USE petscmat
>>>>>>>>>> USE petscksp
>>>>>>>>>> USE petscpc
>>>>>>>>>> USE MPI
>>>>>>>>>>
>>>>>>>>>> Mat :: A
>>>>>>>>>> Vec :: b, x
>>>>>>>>>> PetscInt :: M, I, J, ISLen, NSub
>>>>>>>>>> PetscMPIInt :: size
>>>>>>>>>> PetscErrorCode :: ierr
>>>>>>>>>> PetscScalar :: v
>>>>>>>>>> KSP :: ksp
>>>>>>>>>> PC :: pc
>>>>>>>>>> IS :: subdomains_IS(2), inflated_IS(2)
>>>>>>>>>> PetscInt,DIMENSION(4) :: indices_first_domain
>>>>>>>>>> PetscInt,DIMENSION(36) :: indices_second_domain
>>>>>>>>>>
>>>>>>>>>> call PetscInitialize(PETSC_NULL_CHARACTER, ierr)
>>>>>>>>>> call MPI_Comm_size(PETSC_COMM_WORLD, size, ierr)
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>>>>>>>> ! INTRO: create matrix and right hand side
>>>>>>>>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>>>>>>>>
>>>>>>>>>> WRITE(*,*) "Assembling A,b"
>>>>>>>>>>
>>>>>>>>>> M = 8
>>>>>>>>>> call MatCreateAIJ(PETSC_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
>>>>>>>>>> IF ((I .EQ. J) .AND. (I .LE. 2 )) THEN
>>>>>>>>>> v = 1
>>>>>>>>>> ELSE IF ((I .EQ. J) .AND. (I .GT. 2 )) THEN
>>>>>>>>>> v = 2
>>>>>>>>>> ELSE
>>>>>>>>>> v = 0
>>>>>>>>>> ENDIF
>>>>>>>>>> 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)
>>>>>>>>>>
>>>>>>>>>> call VecCreate(PETSC_COMM_WORLD,b,ierr)
>>>>>>>>>> call VecSetSizes(b, PETSC_DECIDE, M,ierr)
>>>>>>>>>> call VecSetFromOptions(b,ierr)
>>>>>>>>>>
>>>>>>>>>> do I=1,M
>>>>>>>>>> v = 0.5
>>>>>>>>>> call VecSetValue(b,I-1,v, INSERT_VALUES,ierr)
>>>>>>>>>> end do
>>>>>>>>>>
>>>>>>>>>> call VecAssemblyBegin(b,ierr)
>>>>>>>>>> call VecAssemblyEnd(b,ierr)
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>>>>>>>> ! FIRST KSP/PC SETUP
>>>>>>>>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>>>>>>>>
>>>>>>>>>> WRITE(*,*) "KSP/PC first setup"
>>>>>>>>>>
>>>>>>>>>> call KSPCreate(PETSC_COMM_WORLD, ksp, ierr)
>>>>>>>>>> call KSPSetOperators(ksp, A, A, ierr)
>>>>>>>>>> call KSPSetType(ksp, 'preonly', ierr)
>>>>>>>>>> call KSPGetPC(ksp, pc, ierr)
>>>>>>>>>> call KSPSetUp(ksp, ierr)
>>>>>>>>>> call PCSetType(pc, PCGASM, ierr)
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>>>>>>>> ! GASM, SETTING SUBDOMAINS
>>>>>>>>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>>>>>>>>
>>>>>>>>>> WRITE(*,*) "Setting GASM subdomains"
>>>>>>>>>>
>>>>>>>>>> ! Let's create the subdomain IS and inflated_IS
>>>>>>>>>> ! They are equal if no overlap is present
>>>>>>>>>> ! They are 1: 0,1,8,9
>>>>>>>>>> ! 2: 10,...,15,18,...,23,...,58,...,63
>>>>>>>>>>
>>>>>>>>>> indices_first_domain = [0,1,8,9] ! corresponds to diag(1,1)
>>>>>>>>>> do I=0,5
>>>>>>>>>> do J=0,5
>>>>>>>>>> indices_second_domain(I*6+1+J) = 18 + J + 8*I ! corresponds to diag(2,2,...,2)
>>>>>>>>>> !WRITE(*,*) I*6+1+J, 18 + J + 8*I
>>>>>>>>>> end do
>>>>>>>>>> end do
>>>>>>>>>>
>>>>>>>>>> ! Convert into IS
>>>>>>>>>> ISLen = 4
>>>>>>>>>> call ISCreateGeneral(PETSC_COMM_WORLD,ISLen,indices_first_domain,
>>>>>>>>>> & PETSC_COPY_VALUES, subdomains_IS(1), ierr)
>>>>>>>>>> call ISCreateGeneral(PETSC_COMM_WORLD,ISLen,indices_first_domain,
>>>>>>>>>> & PETSC_COPY_VALUES, inflated_IS(1), ierr)
>>>>>>>>>> ISLen = 36
>>>>>>>>>> call ISCreateGeneral(PETSC_COMM_WORLD,ISLen,indices_second_domain,
>>>>>>>>>> & PETSC_COPY_VALUES, subdomains_IS(2), ierr)
>>>>>>>>>> call ISCreateGeneral(PETSC_COMM_WORLD,ISLen,indices_second_domain,
>>>>>>>>>> & PETSC_COPY_VALUES, inflated_IS(2), ierr)
>>>>>>>>>>
>>>>>>>>>> NSub = 2
>>>>>>>>>> call PCGASMSetSubdomains(pc,NSub,
>>>>>>>>>> & subdomains_IS,inflated_IS,ierr)
>>>>>>>>>> call PCGASMDestroySubdomains(NSub,
>>>>>>>>>> & subdomains_IS,inflated_IS,ierr)
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>>>>>>>> ! GASM: SET SUBSOLVERS
>>>>>>>>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>>>>>>>>
>>>>>>>>>> WRITE(*,*) "Setting subsolvers for GASM"
>>>>>>>>>>
>>>>>>>>>> call PCSetUp(pc, ierr) ! should I add this?
>>>>>>>>>>
>>>>>>>>>> call PetscOptionsSetValue(PETSC_NULL_OPTIONS,
>>>>>>>>>> & "-sub_pc_type", "lu", ierr)
>>>>>>>>>> call PetscOptionsSetValue(PETSC_NULL_OPTIONS,
>>>>>>>>>> & "-sub_ksp_type", "preonly", ierr)
>>>>>>>>>>
>>>>>>>>>> call KSPSetFromOptions(ksp, ierr)
>>>>>>>>>> call PCSetFromOptions(pc, ierr)
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>>>>>>>> ! DUMMY SOLUTION: DID IT WORK?
>>>>>>>>>> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>>>>>>>>>>
>>>>>>>>>> WRITE(*,*) "Solve"
>>>>>>>>>>
>>>>>>>>>> call VecDuplicate(b,x,ierr)
>>>>>>>>>> call KSPSolve(ksp,b,x,ierr)
>>>>>>>>>>
>>>>>>>>>> call MatDestroy(A, ierr)
>>>>>>>>>> call KSPDestroy(ksp, ierr)
>>>>>>>>>> call PetscFinalize(ierr)
>>>>>>>>>>
>>>>>>>>>> This code is failing in multiple points. At call PCSetUp(pc, ierr) it produces:
>>>>>>>>>>
>>>>>>>>>> [0]PETSC ERROR: Argument out of range
>>>>>>>>>> [0]PETSC ERROR: Scatter indices in ix are out of range
>>>>>>>>>> ...
>>>>>>>>>> [0]PETSC ERROR: #1 VecScatterCreate() at ***\src\vec\is\sf\INTERF~1\vscat.c:736
>>>>>>>>>> [0]PETSC ERROR: #2 PCSetUp_GASM() at ***\src\ksp\pc\impls\gasm\gasm.c:433
>>>>>>>>>> [0]PETSC ERROR: #3 PCSetUp() at ***\src\ksp\pc\INTERF~1\precon.c:994
>>>>>>>>>>
>>>>>>>>>> And at call KSPSolve(ksp,b,x,ierr) it produces:
>>>>>>>>>>
>>>>>>>>>> forrtl: severe (157): Program Exception - access violation
>>>>>>>>>>
>>>>>>>>>> The index sets are setup coherently with the outputs of e.g. https://gitlab.com/petsc/petsc/-/blob/main/src/ksp/ksp/tests/output/ex71f_1.out: in particular each element of the matrix A corresponds to a number from 0 to 63.
>>>>>>>>>
>>>>>>>>> This is not correct, I believe. The indices are row/col indices, not indices into dense blocks, so for
>>>>>>>>> your example, they are all in [0, 8].
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>>
>>>>>>>>> Matt
>>>>>>>>>
>>>>>>>>>> Note that each submatrix does not represent some physical subdomain, the subdivision is just at the algebraic level.
>>>>>>>>>> I thus have the following questions:
>>>>>>>>>> is this the correct way of creating the IS objects, given my objective at the beginning of the email? Is the ordering correct?
>>>>>>>>>> what am I doing wrong that is generating the above errors?
>>>>>>>>>> Thanks for the patience and the time.
>>>>>>>>>> Best,
>>>>>>>>>> Leonardo
>>>>>>>>>>
>>>>>>>>>> Il giorno ven 5 mag 2023 alle ore 18:43 Barry Smith <bsmith at petsc.dev <mailto:bsmith at petsc.dev>> ha scritto:
>>>>>>>>>>>
>>>>>>>>>>> Added in barry/2023-05-04/add-pcgasm-set-subdomains see also https://gitlab.com/petsc/petsc/-/merge_requests/6419
>>>>>>>>>>>
>>>>>>>>>>> Barry
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>> On May 4, 2023, at 11:23 AM, LEONARDO MUTTI <leonardo.mutti01 at universitadipavia.it <mailto: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.
>>>>>>>>>>>> Thank you again.
>>>>>>>>>>>> Best,
>>>>>>>>>>>> Leonardo
>>>>>>>>>>>>
>>>>>>>>>>>> Il giorno sab 29 apr 2023 alle ore 20:30 Barry Smith <bsmith at petsc.dev <mailto: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 <mailto: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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