[petsc-users] how to use petsc4py with mpi subcommunicators?

[Rodrigo Felicio]

Going over my older codes I found out that I have already tried the approach of splitting PETSc.COMM_WORLD, but whenever I try to create a matrix using a subcommuicator, the program fails. For example, executing the following python code attached to this msg,  I get the following output

time mpirun -n 5 python another_split_ex.py
petsc rank=2, petsc size=5
petsc rank=3, petsc size=5
petsc rank=0, petsc size=5
petsc rank=1, petsc size=5
petsc rank=4, petsc size=5
number of subcomms = 2
sub rank 0/3, color:0
sub rank 0/2, color:1
sub rank 1/3, color:0
sub rank 1/2, color:1
sub rank 2/3, color:0
creating A in subcomm 1= 2, 1
creating A in subcomm 1= 2, 0
Traceback (most recent call last):
  File "another_split_ex.py", line 43, in <module>
Traceback (most recent call last):
  File "another_split_ex.py", line 43, in <module>
    A = PETSc.Mat().createDense([n,n], comm=subcomm)
  File "PETSc/Mat.pyx", line 390, in petsc4py.PETSc.Mat.createDense (src/petsc4py.PETSc.c:113792)
    A = PETSc.Mat().createDense([n,n], comm=subcomm)
  File "PETSc/Mat.pyx", line 390, in petsc4py.PETSc.Mat.createDense (src/petsc4py.PETSc.c:113792)
  File "PETSc/petscmat.pxi", line 602, in petsc4py.PETSc.Mat_Create (src/petsc4py.PETSc.c:25274)
  File "PETSc/petscmat.pxi", line 602, in petsc4py.PETSc.Mat_Create (src/petsc4py.PETSc.c:25274)
  File "PETSc/petscsys.pxi", line 104, in petsc4py.PETSc.Sys_Layout (src/petsc4py.PETSc.c:13666)
  File "PETSc/petscsys.pxi", line 104, in petsc4py.PETSc.Sys_Layout (src/petsc4py.PETSc.c:13666)
petsc4py.PETSc.Error: petsc4py.PETSc.Errorerror code 608517
[1] PetscSplitOwnership() line 86 in ~/mylocal/petsc/src/sys/utils/psplit.c
: error code 134826245
[3] PetscSplitOwnership() line 86 in ~/mylocal/petsc/src/sys/utils/psplit.c


Checking the traceback, all I can say is that when the subcommunicator object reaches psplit.c code it gets somehow corrupted, because PetscSplitOwnership() fails to retrieve the size of the subcommunicator ... :-(

regards
Rodrigo

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