anchor.diff:    !do i = 0, num_procs-1
     call HYPRE_StructGridSetExtents(hypre_grid, ilower(myid,:),iupper(myid,:), ierr)
     !end do
  +
  +  call HYPRE_StructGridSetPeriodic(hypre_grid, [nx, ny], ierr)
   
     call HYPRE_StructGridAssemble(hypre_grid, ierr)
   #endif
  
positive.code:   integer,   intent(in)  :: iupper(0:num_procs-1,2)
    integer,   intent(in)  :: num_procs
    integer,   intent(in)  :: myid
    integer,   intent(out)  :: ierr
  
  #ifdef useExtSolver
  
negative.code: ! ---------------------------------------------------------------------------
  
  subroutine create_Hypre_grid(MPI_COMM_WORLD, hypre_grid, ilower, iupper, &
            num_procs, myid, nx, ny, ierr)
    implicit none
  
    integer,   intent(in)  :: MPI_COMM_WORLD
  