def Lz(self,*args,**kwargs):
        """
        NAME:
           Lz
        PURPOSE:
           calculate the z component of the angular momentum
        INPUT:
           (none)
        OUTPUT:
           z-component of the angular momentum
        HISTORY:
           2018-08-29 - Written - Bovy (UofT)
        """
        tL= self.L(*args,use_physical=False)
        if len(tL.shape) == 2: # 3D orbit
            return tL[:,2]
        else: # 2D orbit
            return tL
NAME:
           Lz
        PURPOSE:
           calculate the z component of the angular momentum
        INPUT:
           (none)
        OUTPUT:
           z-component of the angular momentum
        HISTORY:
           2018-08-29 - Written - Bovy (UofT)