anchor.diff:    integer,          intent(in)  :: MPI_COMM_WORLD
     integer*8,        intent(in)  :: hypre_A
     integer*8,        intent(in)  :: hypre_grid
  +  integer,          intent(in)  :: myid
     integer,          intent(in)  :: num_procs
     integer,          intent(in)  :: ilower(0:num_procs-1,2)
     integer,          intent(in)  :: iupper(0:num_procs-1,2)
  
positive.code: #endif
  
  #ifdef useExtSolver
    call Ext_solver(MPI_COMM_WORLD, hypre_A, hypre_grid, num_procs, &
      ilower, iupper, etastar, &
      etanew, nx, ny, dt, maxits, eps, ierr)
  #endif
  
negative.code: 
  ! ---------------------------------------------------------------------------
  
  subroutine Ext_solver(MPI_COMM_WORLD, hypre_A, hypre_grid, myid, num_procs, &
      ilower, iupper, etastar, &
      etanew, nx, ny, dt, maxits, eps, ierr)
    implicit none
  