def omegac(self,R):
        """
        
        NAME:
        
            omegac
        
        PURPOSE:
        
            calculate the circular angular speed at R in potential Pot

        INPUT:
        
            Pot - Potential instance or list of such instances
        
            R - Galactocentric radius (can be Quantity)
        
        OUTPUT:
        
            circular angular speed
        
        HISTORY:
        
            2011-10-09 - Written - Bovy (IAS)
        
        """
        return nu.sqrt(-self.Rforce(R,use_physical=False)/R)
NAME:
        
            omegac
        
        PURPOSE:
        
            calculate the circular angular speed at R in potential Pot

        INPUT:
        
            Pot - Potential instance or list of such instances
        
            R - Galactocentric radius (can be Quantity)
        
        OUTPUT:
        
            circular angular speed
        
        HISTORY:
        
            2011-10-09 - Written - Bovy (IAS)