anchor.diff:  program aronnax
     implicit none
   
  -#ifdef useExtSolver
     include 'mpif.h'
   
     integer, parameter :: HYPRE_PARCSR = 5555
  -#endif
   
     integer, parameter :: layerwise_input_length = 10000
     ! Resolution
  
positive.code:   integer, dimension(:,:), allocatable :: ilower, iupper
    integer, dimension(:,:), allocatable :: jlower, jupper
    integer*8 :: hypre_grid
  #ifdef useExtSolver
    integer :: i, j
    integer   :: offsets(2,5)
  #endif
  
  
    ! Set default values here
  
negative.code: 
  ! ---------------------------------------------------------------------------
  
  subroutine create_Hypre_grid(MPI_COMM_WORLD, hypre_grid, ilower, iupper, &
            num_procs, ierr)
  
    integer, intent(in) :: MPI_COMM_WORLD
    integer*8 :: hypre_grid
    integer :: num_procs
    integer :: ilower(0:num_procs-1,2), iupper(0:num_procs-1,2)
  
    call Hypre_StructGridCreate(MPI_COMM_WORLD, 2, hypre_grid, ierr)
  
    !do i = 0, num_procs-1
    call HYPRE_StructGridSetExtents(hypre_grid, ilower(myid,:),iupper(myid,:), ierr)
    !end do
  
    call HYPRE_StructGridAssemble(hypre_grid, ierr)
  
    return
  end subroutine create_Hypre_grid
  
  ! ---------------------------------------------------------------------------
  
  subroutine Ext_solver(hypre_A, MPI_COMM_WORLD, num_procs, & 
      ilower, iupper, etastar, &
      etanew, nx, ny, dt, hypre_grid, maxits, eps)
  