code: def potentialStaeckel(u,v,pot,delta):
      
      R,z= bovy_coords.uv_to_Rz(u,v,delta=delta)
      return _evaluatePotentials(pot,R,z)
docs: NAME:
         potentialStaeckel
      PURPOSE:
         return the potential
      INPUT:
         u - confocal u
         v - confocal v
         pot - potential
         delta - focus
      OUTPUT:
         Phi(u,v)
      HISTORY:
         2012-11-29 - Written - Bovy (IAS)