anchor.diff:  
     call HYPRE_StructVectorAssemble(hypre_b, ierr)
   
  -
  -
  -
  +  ! now create the x vector
     call HYPRE_StructVectorCreate(MPI_COMM_WORLD, hypre_grid, hypre_x, ierr)
     call HYPRE_StructVectorInitialize(hypre_x, ierr)
   
  
positive.code:   ! field that removes it
    call calc_eta_star(ub, vb, eta, etastar, freesurfFac, nx, ny, dx, dy, dt)
    ! print *, maxval(abs(etastar))
  
  
    ! Prevent barotropic signals from bouncing around outside the
    ! wet region of the model.
  
negative.code:           g_vec, nx, ny, layers, n, &
            MPI_COMM_WORLD, myid, num_procs, ilower, iupper, &
            hypre_grid, hypre_A, ierr)
  
      end if
  
  