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

  5:   use petscvec
  6:   use petscmat

  8:   implicit none

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

 17:   PetscCallA(PetscInitialize(ierr))

 19:   allocate (dnnz(0:m - 1))
 20:   allocate (onnz(0:m - 1))

 22:   do i = 0, m - 1
 23:     dnnz(i) = 1
 24:     onnz(i) = 1
 25:   end do

 27:   PetscCallA(MatCreateAIJ(PETSC_COMM_WORLD, m, n, PETSC_DETERMINE, PETSC_DETERMINE, PETSC_DECIDE, dnnz, PETSC_DECIDE, onnz, A, ierr))
 28:   PetscCallA(MatSetFromOptions(A, ierr))
 29:   PetscCallA(MatSetUp(A, ierr))
 30:   deallocate (dnnz)
 31:   deallocate (onnz)

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

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

 52: end program

 54: !/*TEST
 55: !
 56: !   test:
 57: !      suffix: 1
 58: !      output_file: output/ex4_1.out
 59: !
 60: !   test:
 61: !      suffix: 2
 62: !      nsize: 2
 63: !      output_file: output/ex4_2.out
 64: !
 65: !TEST*/