anchor.diff:  ! ... The velocity field follows:
   ! ...      u = - dPsi/dy
   ! ...      v =   dPsi/dx
  +! ... Version 0.1, released October 2017
   ! *********************************************************************
   
   use cosmo
  
positive.code: 
  else
  
  endif
  
  
  
  call stop_error(0,'Ok')
  
  
negative.code:   real(dp), intent(in)     :: x,y
    real(dp)                 :: psi
  
    psi = half*(x*x+y*y+x*y)
  
    end function psifunc
  
  