def oortC(self,R,romberg=False,nsigma=None,phi=0.):
        """
        NAME:

           oortC

        PURPOSE:

           calculate the Oort function C

        INPUT:

           R - radius at which to calculate C (can be Quantity)

        OPTIONAL INPUT:

           nsigma - number of sigma to integrate the velocities over

        KEYWORDS:

           romberg - if True, use a romberg integrator (default: False)

        OUTPUT:

           Oort C at R

        HISTORY:

           2011-04-19 - Written - Bovy (NYU)

        BUGS:

           could be made more efficient, e.g., surfacemass is calculated multiple times
           we know this is zero, but it is calculated anyway (bug or feature?)

        """
        #2C= -meanvR/R-dmeanvphi/R/dphi+dmeanvR/dR
        meanvr= self.meanvR(R,romberg=romberg,nsigma=nsigma,phi=phi,
                            use_physical=False)
        dmeanvphiRdphi= 0. #We know this, since the DF does not depend on phi
        surfmass= self._vmomentsurfacemass(R,0,0,phi=phi,romberg=romberg,nsigma=nsigma)
        dmeanvRdR= self._vmomentsurfacemass(R,1,0,deriv='R',phi=phi,romberg=romberg,nsigma=nsigma)/\
            surfmass #other terms is zero because f is even in vR
        return 0.5*(-meanvr/R-dmeanvphiRdphi/R+dmeanvRdR)