anchor.diff:    double precision :: H0 ! default depth in no file specified
     ! Pressure solver variables
     double precision :: a(5, nx, ny)
  -  double precision :: phi(0:nx+1, 0:ny+1), phiold(0:nx+1, 0:ny+1)
   
     ! Bernoulli potential and relative vorticity
     double precision :: b(0:nx+1, 0:ny+1, layers)
  
positive.code:   double precision rjac, eps
    double precision rhs(nx, ny)
    double precision res(nx, ny)
    double precision norm, norm0, norm_old
    double precision relax_param
    character(30) Format
  
    rhs = -etastar(1:nx,1:ny)/dt**2
    ! first guess for etanew
  
negative.code:     call wrap_fields_2D(etanew, nx, ny)
  
      if (nit.gt.1.and.norm.lt.eps*norm0) then
  
        return
  
      end if
    end do
  
  