Dear PETSc team,
I would like to create two matrices. The first matrix is based on a compact
stencil (COMPACT), and the second one has an extended stencil (WIDE)
So the non-zero elements of the COMPACT matrix is contained in the WIDE matrix
as well. But the WIDE matrix shall contain some additional elements.
I try to create the COMPACT matrix first, then copy it to the WIDE matrix and
then add some more terms to the WIDE matrix.
We want to create a matrix that is based on a lower order approximation of our
scheme which serves as basis matrix for preconditioning,
where we want to have a more accurate jacobian which has a larger stencil, that
is based on the lower approximation plus some additional non-zero elements.
We want to avoid that we have to call the same routines twice to setup the more
accurate matrix, but copy the elements from the lower order (compact) matrix.
I try to use MatCopy to copy the COMPACT matrix into the WIDE matrix. Somehow I
cannot figure out to do this,
since there is always a problem wirh non conforming sizes
[0]PETSC ERROR: Nonconforming object sizes
[0]PETSC ERROR: Mat A,Mat B: global dim (4,8) (4,8)
Here is a basic example that I try.
Adding additional elements to the WIDE matrix is disabled right now, since
MatCopy already gives a problem.
I thought that in MatCopy(COMPACT, WIDE, DIFFERENT_NONZERO_PATTERN, ierr)
the option DIFFERENT_NONZERO_PATTERN should enable to copy different matrix
sizes into each other.
Or is that not possible to do ?!
Here the COMPACT matrix is a 4x4 matrix and the WIDE matrix 8x8, for a basic
test.
Thanks, Frank Bramkamp
program petsc_matrix_example
#include <petsc/finclude/petsc.h>
use petsc
implicit none
PetscErrorCode :: ierr
Mat :: COMPACT, WIDE
PetscInt :: m, n, MM, NN, d_nz
PetscInt :: i, j
PetscScalar :: additional_value
! Initialize PETSc
call PetscInitialize(PETSC_NULL_CHARACTER, ierr)
! Set dimensions for COMPACT matrix
m = 4 ! Local rows
n = 4 ! Local columns
MM = 4 ! Global rows
NN = 4 ! Global columns
d_nz = 4 ! Estimated non-zeros per row (diagonal) o_nz = 0 ! Estimated
non-zeros per row (off-diagonal)
! Create COMPACT matrix
call MatCreateSeqAIJ(PETSC_COMM_SELF, MM, NN, PETSC_DECIDE,
PETSC_NULL_INTEGER, COMPACT, ierr)
! Set some values in COMPACT matrix (example) do i = 0, M-1
do i = 0, NN-1
!do j = max(0, i-1), min(NN-1, i+1)
do j = 0,NN-1
call MatSetValue(COMPACT, i, j, 1.0_PETSC_REAL_KIND, INSERT_VALUES, ierr)
end do
end do
! Assemble COMPACT matrix
call MatAssemblyBegin(COMPACT, MAT_FINAL_ASSEMBLY, ierr)
call MatAssemblyEnd(COMPACT, MAT_FINAL_ASSEMBLY, ierr)
! Set dimensions for WIDE matrix
n = 8 ! Increase local columns
NN = 8 ! Increase global columns
m = 8
MM = 8
d_nz = 8
! Create WIDE matrix
call MatCreateSeqAIJ(PETSC_COMM_SELF, MM, NN, PETSC_DECIDE,
PETSC_NULL_INTEGER, WIDE, ierr)
! Assemble WIDE matrix: MUST WE ASSMBLE THE MATRIX BEFORE MatCOPY ?!
call MatAssemblyBegin(WIDE, MAT_FINAL_ASSEMBLY, ierr)
call MatAssemblyEnd(WIDE, MAT_FINAL_ASSEMBLY, ierr)
! Copy elements from COMPACT to WIDE
call MatCopy(COMPACT, WIDE, DIFFERENT_NONZERO_PATTERN, ierr)
!call MatAssemblyBegin(WIDE, MAT_FINAL_ASSEMBLY, ierr)
! Add additional elements to WIDE matrix
!!$ additional_value = 10.0
!!$
!!$ ! original
!!$ !do i = 0, MM-1
!!$ ! do j = NN/2, NN-1
!!$ ! call MatSetValue(WIDE, i, j, additional_value, INSERT_VALUES, ierr)
!!$ ! end do
!!$ !end do
!!$
!!$ do i = 0, NN-1
!!$ do j = max(0, i-1), min(NN-1, i+1)
!!$ call MatSetValue(WIDE, i, j, 10.0_PETSC_REAL_KIND, ADD_VALUES, ierr)
!!$ end do
!!$ end do
! Assemble WIDE matrix again
call MatAssemblyBegin(WIDE, MAT_FINAL_ASSEMBLY, ierr)
call MatAssemblyEnd(WIDE, MAT_FINAL_ASSEMBLY, ierr)
! View matrices (optional)
call PetscPrintf(PETSC_COMM_WORLD, "COMPACT matrix:\n", ierr)
call MatView(COMPACT, PETSC_VIEWER_STDOUT_WORLD, ierr)
call PetscPrintf(PETSC_COMM_WORLD, "WIDE matrix:\n", ierr)
call MatView(WIDE, PETSC_VIEWER_STDOUT_WORLD, ierr)
! Clean up
call MatDestroy(COMPACT, ierr)
call MatDestroy(WIDE, ierr)
! Finalize PETSc
call PetscFinalize(ierr)
end program petsc_matrix_example
