'Return the density parameter for non-relativistic matter
at redshift ``z``.
Parameters
z : array-like
Input redshifts.
Returns
Om : ndarray, or float if input scalar
The density of non-relativistic matter relative to the critical
density at each redshift.
Notes
This does not include neutrinos, even if non-relativistic
at the redshift of interest; see `Onu`.'

def Om(self, z):

    if isiterable(z):
        z = np.asarray(z)
    return ((self._Om0 * ((1.0 + z) ** 3)) * (self.inv_efunc(z) ** 2))
