code: def _R2deriv(self,R,z,phi=0.,t=0.): #pragma: no cover
          
          raise AttributeError
          # Implementation above does not work bc SCF.R2deriv is not implemented
          r= numpy.sqrt(R**2.+z**2.)
          out= self._scf.R2deriv(R,z,phi=phi,use_physical=False)
          for a,ds,d2s,H in zip(self._Sigma_amp,self._dSigmadR,self._d2SigmadR2,
                                self._Hz):
              out+= 4.*numpy.pi*a*H(z)/r**2.*(d2s(r)*R**2.+z**2./r*ds(r))
          return out
docs: NAME:
             _R2deriv
          PURPOSE:
             evaluate the second radial derivative for this potential
          INPUT:
             R - Galactocentric cylindrical radius
             z - vertical height
             phi - azimuth
             t - time
          OUTPUT:
             the second radial derivative
          HISTORY:
             2016-12-26 - Written - Bovy (UofT/CCA)