def _evaluate(self,R,z,phi=0.,t=0.):
        """
        NAME:
           _evaluate
        PURPOSE:
           evaluate the potential at R,z
        INPUT:
           R - Galactocentric cylindrical radius
           z - vertical height
           phi - azimuth
           t - time
        OUTPUT:
           Phi(R,z)
        HISTORY:
           2016-05-30 - Started - Bovy (UofT)
        """
        if not self.isNonAxi:
            phi= 0.
        x,y,z= bovy_coords.cyl_to_rect(R,phi,z)
        if self._aligned:
            return self._evaluate_xyz(x,y,z)
        else:
            xyzp= numpy.dot(self._rot,numpy.array([x,y,z]))
            return self._evaluate_xyz(xyzp[0],xyzp[1],xyzp[2])
NAME:
           _evaluate
        PURPOSE:
           evaluate the potential at R,z
        INPUT:
           R - Galactocentric cylindrical radius
           z - vertical height
           phi - azimuth
           t - time
        OUTPUT:
           Phi(R,z)
        HISTORY:
           2016-05-30 - Started - Bovy (UofT)