[petsc-users] MatGetLocalToGlobalMapping returning null pointers

[Barry Smith]

  Mat's only have a LocalToGlobal mapping if it is specifically set (for example DMCreateMatrix() usually sets one for you or you can use MatSetLocalToGlobalMapping()) (read the manual page) otherwise the Mat simply does not have the mapping. All this means is one cannot use MatSetValuesLocal() on Mat that do not have a local to global mapping.

In your code below ierr = MatGetOwnershipRange(A,&Istart,&Iend);CHKERRQ(ierr) tells you which global rows are local but note that actually doesn't have anything to do with the local to global mapping.

  Barry


> On Jul 27, 2015, at 2:29 PM, Klinvex, Alicia Marie <amklinv at sandia.gov> wrote:
> 
> Hello,
> 
> I am trying to determine how the rows and columns of my PETSc Mat are being mapped to different MPI processes.  I call MatGetLocalToGlobalMapping, but the ISLocalToGlobalMapping obtained for both the rows and columns is null, and I receive the following error message when I call ISLocalToGlobalMappingGetSize:
> 
> [1]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
> [1]PETSC ERROR: Null argument, when expecting valid pointer
> [1]PETSC ERROR: Null Object: Parameter # 1
> [1]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html for trouble shooting.
> [1]PETSC ERROR: Petsc Release Version 3.6.0, Jun, 09, 2015
> [1]PETSC ERROR: ./AnasaziTest.exe on a arch-linux2-cxx-debug named hardin.srn.sandia.gov by amklinv Mon Jul 27 10:25:35 2015
> [1]PETSC ERROR: Configure options --with-blas-lib=/home/amklinv/lapack-3.5.0/librefblas.a --with-lapack-lib=/home/amklinv/lapack-3.5.0/liblapack.a --with-mpi-dir=/projects/install/rhel6-x86_64/sems/compiler/gcc/4.7.2/openmpi/1.6.5 --prefix=/home/amklinv/PETSc/petsc_install --with-shared-libraries=0 --with-cxx-dialect=C++11 --with-c++-support --with-clanguage=cxx --download-superlu_dist --download-superlu --download-hypre --download-metis --download-parmetis
> [1]PETSC ERROR: #1 ISLocalToGlobalMappingGetSize() line 55 in /home/amklinv/PETSc/petsc-3.6.0/src/vec/is/utils/isltog.c
> [1]PETSC ERROR: #2 Tpetra_PETScAIJRowGraph() line 247 in Tpetra_PETScAIJRowGraph.hpp
> [2]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
> 
> Does this mean I set up the matrix incorrectly, or is there a different function I should be calling instead?
> 
> The relevant pieces of source code are below (although I would be happy to provide additional information if it would prove useful).
> 
> Thank you,
> Alicia Klinvex
> 
> 
> 
>   Mat            A;        /* PETSc matrix */
> 
>   PetscInitialize(&argc,&args,(char *)0,help);
> 
>   ierr = MatCreate(PETSC_COMM_WORLD,&A);CHKERRQ(ierr);
>   ierr = MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,m*n,m*n);CHKERRQ(ierr);
>   ierr = MatSetType(A, MATAIJ);CHKERRQ(ierr);
>   ierr = MatSetFromOptions(A);CHKERRQ(ierr);
>   ierr = MatMPIAIJSetPreallocation(A,5,PETSC_NULL,5,PETSC_NULL);CHKERRQ(ierr);
>   ierr = MatSetUp(A);CHKERRQ(ierr);
>   PetscObjectGetComm( (PetscObject)A, &comm);
>   ierr = MPI_Comm_rank(comm,&rank);CHKERRQ(ierr);
>   if (!rank) printf("Matrix has %d (%dx%d) rows\n",m*n,m,n);
> 
>   ierr = MatGetOwnershipRange(A,&Istart,&Iend);CHKERRQ(ierr);
> 
>   for (Ii=Istart; Ii<Iend; Ii++) { 
>     v = -1.0; i = Ii/n; j = Ii - i*n;  
>     if (i>0)   {J = Ii - n; ierr = MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);CHKERRQ(ierr);}
>     if (i<m-1) {J = Ii + n; ierr = MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);CHKERRQ(ierr);}
>     if (j>0)   {J = Ii - 1; ierr = MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);CHKERRQ(ierr);}
>     if (j<n-1) {J = Ii + 1; ierr = MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);CHKERRQ(ierr);}
>     v = 4.0; ierr = MatSetValues(A,1,&Ii,1,&Ii,&v,INSERT_VALUES);CHKERRQ(ierr);
>   }
> 
>   ierr = MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
>   ierr = MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
> 
> ...
>  
>  ISLocalToGlobalMapping PETScRowOwnership, PETScColOwnership;
>  
>   ierr = MatGetLocalToGlobalMapping(A, &PETScRowOwnership, &PETScColOwnership); CHKERRV(ierr);
>   ierr = ISLocalToGlobalMappingGetSize(PETScRowOwnership, &PETScLocalCols); CHKERRV(ierr);