def calcu0(self,E,Lz):
        """
        NAME:
           calcu0
        PURPOSE:
           calculate the minimum of the u potential
        INPUT:
           E - energy
           Lz - angular momentum
        OUTPUT:
           u0
        HISTORY:
           2012-11-29 - Written - Bovy (IAS)
        """                           
        logu0= optimize.brent(_u0Eq,
                              args=(self._delta,self._pot,
                                    E,Lz**2./2.))
        return numpy.exp(logu0)