'Evaluates the redshift dependence of the dark energy density.
Parameters
z : array-like
Input redshifts.
Returns
I : ndarray, or float if input scalar
The scaling of the energy density of dark energy with redshift.
Notes
The scaling factor, I, is defined by :math:`\rho(z) = \rho_0 I`,
and in this case is given by
:math:`I = \left(1 + z\right)^{3\left(1 + w_0\right)}`'

def de_density_scale(self, z):

    if isiterable(z):
        z = np.asarray(z)
    return ((1.0 + z) ** (3.0 * (1.0 + self._w0)))
