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:   PetscReal,parameter ::  two =2.0, one = 1.0
 13:   PetscInt,pointer,dimension(:) ::  dnnz,onnz
 14:   PetscInt    ::  i,rstart,rend,M1,N1
 15:   PetscErrorCode  ierr

 17:   call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
 18: 
 19:   if (ierr /= 0) then
 20:    print*,'PetscInitialize failed'
 21:    stop
 22:   endif
 23: 
 24: 
 25:   allocate(dnnz(0:m-1))
 26:   allocate(onnz(0:m-1))
 27: 
 28:   do i=0,m-1
 29:    dnnz(i) = 1
 30:    onnz(i) = 1
 31:   end do
 32: 
 33:   call MatCreateAIJ(MPI_COMM_WORLD,m,n,PETSC_DETERMINE,PETSC_DETERMINE,PETSC_DECIDE,dnnz,PETSC_DECIDE,onnz,A,ierr);CHKERRA(ierr)
 34:   call MatSetFromOptions(A,ierr);CHKERRA(ierr)
 35:   call MatSetUp(A,ierr);CHKERRA(ierr)
 36:   deallocate(dnnz)
 37:   deallocate(onnz)

 39:   !/* This assembly shrinks memory because we do not insert enough number of values */
 40:   call MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY,ierr);CHKERRA(ierr)
 41:   call MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY,ierr);CHKERRA(ierr)

 43:   !/* MatResetPreallocation restores the memory required by users */
 44:   call MatResetPreallocation(A,ierr);CHKERRA(ierr)
 45:   call MatSetOption(A,MAT_NEW_NONZERO_ALLOCATION_ERR,PETSC_TRUE,ierr);CHKERRA(ierr)
 46:   call MatGetOwnershipRange(A,rstart,rend,ierr);CHKERRA(ierr)
 47:   call MatGetSize(A,M1,N1,ierr);CHKERRA(ierr)
 48:   do i=rstart,rend-1
 49:    call MatSetValue(A,i,i,two,INSERT_VALUES,ierr);CHKERRA(ierr)
 50:    if (rend<N1) call MatSetValue(A,i,rend,one,INSERT_VALUES,ierr);CHKERRA(ierr)
 51:   end do
 52:   call MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY,ierr);CHKERRA(ierr)
 53:   call MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY,ierr);CHKERRA(ierr)
 54:   call MatView(A,PETSC_VIEWER_STDOUT_WORLD,ierr);CHKERRA(ierr)
 55:   call MatDestroy(A,ierr);CHKERRA(ierr)
 56:   call PetscFinalize(ierr);CHKERRA(ierr)
 57: 
 58: end program