'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 - w_z\right)}
\exp \left(-3 w_z z\right)'

def de_density_scale(self, z):

    if isiterable(z):
        z = np.asarray(z)
    zp1 = (1.0 + z)
    return ((zp1 ** (3.0 * ((1.0 + self._w0) - self._wz))) * np.exp((((-3.0) * self._wz) * z)))
