def density(self, R, Rs, rho0):
        """
        three dimenstional NFW profile

        :param R: radius of interest
        :type R: float/numpy array
        :param Rs: scale radius
        :type Rs: float
        :param rho0: density normalization (characteristic density)
        :type rho0: float
        :return: rho(R) density
        """
        return rho0/(R/Rs*(1+R/Rs)**2)
three dimenstional NFW profile

        :param R: radius of interest
        :type R: float/numpy array
        :param Rs: scale radius
        :type Rs: float
        :param rho0: density normalization (characteristic density)
        :type rho0: float
        :return: rho(R) density