'Scale factor at redshift ``z``.
The scale factor is defined as :math:`a = 1 / (1 + z)`.
Parameters
z : array-like
Input redshifts.
Returns
a : ndarray, or float if input scalar
Scale factor at each input redshift.'

def scale_factor(self, z):

    if isiterable(z):
        z = np.asarray(z)
    return (1.0 / (1.0 + z))
