'Return the density parameter for neutrinos at redshift ``z``.
Parameters
z : array-like
Input redshifts.
Returns
Onu : ndarray, or float if input scalar
The energy density of neutrinos relative to the critical
density at each redshift.  Note that this includes their
kinetic energy (if they have mass), so it is not equal to
the commonly used :math:`\sum \frac{m_{\nu}}{94 eV}`,
which does not include kinetic energy.'

def Onu(self, z):

    if isiterable(z):
        z = np.asarray(z)
        if (self._Onu0 == 0):
            return np.zeros(np.asanyarray(z).shape, dtype=np.float)
    elif (self._Onu0 == 0):
        return 0.0
    return (self.Ogamma(z) * self.nu_relative_density(z))
