def rl(self,lz):
        """
        NAME:
        
            rl
        
        PURPOSE:
        
            calculate the radius of a circular orbit of Lz
        
        INPUT:
        
        
            lz - Angular momentum (can be Quantity)
        
        OUTPUT:
        
            radius
        
        HISTORY:
        
            2012-07-30 - Written - Bovy (IAS@MPIA)
        
        NOTE:
        
            seems to take about ~0.5 ms for a Miyamoto-Nagai potential; 
            ~0.75 ms for a MWPotential
        
        """
        if _APY_LOADED and isinstance(lz,units.Quantity):
            lz= lz.to(units.km/units.s*units.kpc).value/self._vo/self._ro
        return rl(self,lz,use_physical=False)
NAME:
        
            rl
        
        PURPOSE:
        
            calculate the radius of a circular orbit of Lz
        
        INPUT:
        
        
            lz - Angular momentum (can be Quantity)
        
        OUTPUT:
        
            radius
        
        HISTORY:
        
            2012-07-30 - Written - Bovy (IAS@MPIA)
        
        NOTE:
        
            seems to take about ~0.5 ms for a Miyamoto-Nagai potential; 
            ~0.75 ms for a MWPotential