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*/