1: #include <petsc/finclude/petscmat.h>
  2: program main
  3:   use petscmat

  5:   implicit none

  7:   Mat A
  8:   PetscInt, parameter ::  n = 5, m = 5
  9:   PetscScalar, parameter ::  two = 2.0, one = 1.0
 10:   PetscInt, pointer, dimension(:) ::  dnnz, onnz
 11:   PetscInt    ::  i, rstart, rend, M1, N1
 12:   PetscErrorCode ierr

 14:   PetscCallA(PetscInitialize(ierr))

 16:   allocate (dnnz(0:m - 1))
 17:   allocate (onnz(0:m - 1))

 19:   do i = 0, m - 1
 20:     dnnz(i) = 1
 21:     onnz(i) = 1
 22:   end do

 24:   PetscCallA(MatCreateAIJ(PETSC_COMM_WORLD, m, n, PETSC_DETERMINE, PETSC_DETERMINE, PETSC_DECIDE, dnnz, PETSC_DECIDE, onnz, A, ierr))
 25:   PetscCallA(MatSetFromOptions(A, ierr))
 26:   PetscCallA(MatSetUp(A, ierr))
 27:   deallocate (dnnz)
 28:   deallocate (onnz)

 30:   !/* This assembly shrinks memory because we do not insert enough number of values */
 31:   PetscCallA(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY, ierr))
 32:   PetscCallA(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY, ierr))

 34:   !/* MatResetPreallocation restores the memory required by users */
 35:   PetscCallA(MatResetPreallocation(A, ierr))
 36:   PetscCallA(MatSetOption(A, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_TRUE, ierr))
 37:   PetscCallA(MatGetOwnershipRange(A, rstart, rend, ierr))
 38:   PetscCallA(MatGetSize(A, M1, N1, ierr))
 39:   do i = rstart, rend - 1
 40:     PetscCallA(MatSetValue(A, i, i, two, INSERT_VALUES, ierr))
 41:     if (rend < N1) PetscCallA(MatSetValue(A, i, rend, one, INSERT_VALUES, ierr))
 42:   end do
 43:   PetscCallA(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY, ierr))
 44:   PetscCallA(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY, ierr))
 45:   PetscCallA(MatView(A, PETSC_VIEWER_STDOUT_WORLD, ierr))
 46:   PetscCallA(MatDestroy(A, ierr))
 47:   PetscCallA(PetscFinalize(ierr))

 49: end program

 51: !/*TEST
 52: !
 53: !   test:
 54: !      suffix: 1
 55: !      output_file: output/ex4_1.out
 56: !
 57: !   test:
 58: !      suffix: 2
 59: !      nsize: 2
 60: !      output_file: output/ex4_2.out
 61: !
 62: !TEST*/