anchor.diff:  
   !> Calculate the barotropic v velocity
   subroutine calc_baro_v(vb,v,h,eta,freesurfFac,nx,ny,layers)
  +  implicit none
   
     integer nx,ny,layers
     integer i,j,k
  
positive.code: !> Evaluate relative vorticity at lower left grid boundary (du/dy
  !! and dv/dx are at lower left corner as well)
  subroutine evaluate_zeta(zeta,u,v,nx,ny,layers,dx,dy)
    integer nx,ny,layers
    integer i,j,k
    double precision h(0:nx,0:ny,layers)
  
negative.code: !> Check to see if there are any NaNs in the data field and stop the
  !! calculation if any are found.
  subroutine break_if_NaN(data,nx,ny,layers,n)
    implicit none
  
    ! To stop the program if it detects at NaN in the variable being checked
  
    integer nx,ny,layers,n,i,j,k
    double precision data(0:nx+1, 0:ny+1,layers)
  
    do k=1,layers
  