# Licensed under a 3-clause BSD style license - see LICENSE.rst
from __future__ import (absolute_import, division, print_function,
                        unicode_literals)

from ..extern import six

import sys
from math import sqrt, pi, exp, log, floor
from abc import ABCMeta, abstractmethod

import numpy as np

from .. import constants as const
from ..utils.misc import isiterable, deprecated
from .. import units as u
from ..utils.state import ScienceState, ScienceStateAlias

from . import parameters

# Originally authored by Andrew Becker (becker@astro.washington.edu),
# and modified by Neil Crighton (neilcrighton@gmail.com) and Roban
# Kramer (robanhk@gmail.com).

# Many of these adapted from Hogg 1999, astro-ph/9905116
# and Linder 2003, PRL 90, 91301

__all__ = ["FLRW", "LambdaCDM", "FlatLambdaCDM", "wCDM", "FlatwCDM",
           "Flatw0waCDM", "w0waCDM", "wpwaCDM", "w0wzCDM", "get_current",
           "set_current", "WMAP5", "WMAP7", "WMAP9", "Planck13",
           "default_cosmology"]

__doctest_requires__ = {'*': ['scipy.integrate']}

# Some conversion constants -- useful to compute them once here
#  and reuse in the initialization rather than have every object do them
# Note that the call to cgs is actually extremely expensive,
#  so we actually skip using the units package directly, and
#  hardwire the conversion from mks to cgs. This assumes that constants
#  will always return mks by default -- if this is made faster for simple
#  cases like this, it should be changed back.
# Note that the unit tests should catch it if this happens
H0units_to_invs = (u.km / (u.s * u.Mpc)).to(1.0 / u.s)
sec_to_Gyr = u.s.to(u.Gyr)
# const in critical density in cgs units (g cm^-3)
critdens_const = 3. / (8. * pi * const.G.value * 1000)
arcsec_in_radians = pi / (3600. * 180)
arcmin_in_radians = pi / (60. * 180)
# Radiation parameter over c^2 in cgs (g cm^-3 K^-4)
a_B_c2 = 4e-3 * const.sigma_sb.value / const.c.value ** 3
# Boltzmann constant in eV / K
kB_evK = const.k_B.to(u.eV / u.K)


class CosmologyError(Exception):
    pass


class Cosmology(object):
    """ Placeholder for when a more general Cosmology class is
    implemented. """


@six.add_metaclass(ABCMeta)
class FLRW(Cosmology):
    """ A class describing an isotropic and homogeneous
    (Friedmann-Lemaitre-Robertson-Walker) cosmology.

    This is an abstract base class -- you can't instantiate
    examples of this class, but must work with one of its
    subclasses such as `LambdaCDM` or `wCDM`.

    Parameters
    ----------

    H0 : float or scalar `~astropy.units.Quantity`
        Hubble constant at z = 0.  If a float, must be in [km/sec/Mpc]

    Om0 : float
        Omega matter: density of non-relativistic matter in units of the
        critical density at z=0.

    Ode0 : float
        Omega dark energy: density of dark energy in units of the critical
        density at z=0.

    Tcmb0 : float or scalar `~astropy.units.Quantity`
        Temperature of the CMB z=0. If a float, must be in [K]. Default: 2.725.
        Setting this to zero will turn off both photons and neutrinos (even
        massive ones)

    Neff : float
        Effective number of Neutrino species. Default 3.04.

    m_nu : `~astropy.units.Quantity`
        Mass of each neutrino species. If this is a scalar Quantity, then all
        neutrino species are assumed to have that mass. Otherwise, the mass of
        each species. The actual number of neutrino species (and hence the
        number of elements of m_nu if it is not scalar) must be the floor of
        Neff. Usually this means you must provide three neutrino masses unless
        you are considering something like a sterile neutrino.

    name : str
        Optional name for this cosmological object.

    Notes
    -----
    Class instances are static -- you can't change the values
    of the parameters.  That is, all of the attributes above are
    read only.
    """
    def __init__(self, H0, Om0, Ode0, Tcmb0=2.725, Neff=3.04,
                 m_nu=u.Quantity(0.0, u.eV), name=None):

        # all densities are in units of the critical density
        self._Om0 = float(Om0)
        if self._Om0 < 0.0:
            raise ValueError("Matter density can not be negative")
        self._Ode0 = float(Ode0)
        self._Neff = float(Neff)
        if self._Neff < 0.0:
            raise ValueError("Effective number of neutrinos can "
                             "not be negative")
        self.name = name

        # Tcmb may have units
        self._Tcmb0 = u.Quantity(Tcmb0, unit=u.K, dtype=np.float)
        if not self._Tcmb0.isscalar:
            raise ValueError("Tcmb0 is a non-scalar quantity")

        # Hubble parameter at z=0, km/s/Mpc
        self._H0 = u.Quantity(H0, unit=u.km / u.s / u.Mpc, dtype=np.float)
        if not self._H0.isscalar:
            raise ValueError("H0 is a non-scalar quantity")

        # 100 km/s/Mpc * h = H0 (so h is dimensionless)
        self._h = self._H0.value / 100.
        # Hubble distance
        self._hubble_distance = (const.c / self._H0).to(u.Mpc)
        # H0 in s^-1; don't use units for speed
        H0_s = self._H0.value * H0units_to_invs
        # Hubble time; again, avoiding units package for speed
        self._hubble_time = u.Quantity(sec_to_Gyr / H0_s, u.Gyr)

        # critical density at z=0 (grams per cubic cm)
        cd0value = critdens_const * H0_s ** 2
        self._critical_density0 = u.Quantity(cd0value, u.g / u.cm ** 3)

        # Load up neutrino masses.  Note: in Py2.x, floor is floating
        self._nneutrinos = int(floor(self._Neff))

        # We are going to share Neff between the neutrinos equally.
        # In detail this is not correct, but it is a standard assumption
        # because propertly calculating it is a) complicated b) depends
        # on the details of the massive nuetrinos (e.g., their weak
        # interactions, which could be unusual if one is considering sterile
        # neutrinos)
        self._massivenu = False
        if self._nneutrinos > 0 and self._Tcmb0.value > 0:
            self._neff_per_nu = self._Neff / self._nneutrinos

            # We can't use the u.Quantity constructor as we do above
            # because it doesn't understand equivalencies
            if not isinstance(m_nu, u.Quantity):
                raise ValueError("m_nu must be a Quantity")

            m_nu = m_nu.to(u.eV, equivalencies=u.mass_energy())

            # Now, figure out if we have massive neutrinos to deal with,
            # and, if so, get the right number of masses
            # It is worth the effort to keep track of massless ones seperately
            # (since they are quite easy to deal with, and a common use case
            # is to set only one neutrino to have mass)
            if m_nu.isscalar:
                # Assume all neutrinos have the same mass
                if m_nu.value == 0:
                    self._nmasslessnu = self._nneutrinos
                    self._nmassivenu = 0
                else:
                    self._massivenu = True
                    self._nmasslessnu = 0
                    self._nmassivenu = self._nneutrinos
                    self._massivenu_mass = (m_nu.value *
                                            np.ones(self._nneutrinos))
            else:
                # Make sure we have the right number of masses
                # -unless- they are massless, in which case we cheat a little
                if m_nu.value.min() < 0:
                    raise ValueError("Invalid (negative) neutrino mass"
                                     " encountered")
                if m_nu.value.max() == 0:
                    self._nmasslessnu = self._nneutrinos
                    self._nmassivenu = 0
                else:
                    self._massivenu = True
                    if len(m_nu) != self._nneutrinos:
                        raise ValueError("Unexpected number of neutrino masses")
                    # Segregate out the massless ones
                    try:
                        # Numpy < 1.6 doesn't have count_nonzero
                        self._nmasslessnu = np.count_nonzero(m_nu.value == 0)
                    except AttributeError:
                        self._nmasslessnu = len(np.nonzero(m_nu.value == 0)[0])
                    self._nmassivenu = self._nneutrinos - self._nmasslessnu
                    w = np.nonzero(m_nu.value > 0)[0]
                    self._massivenu_mass = m_nu[w]

        # Compute photon density, Tcmb, neutrino parameters
        # Tcmb0=0 removes both photons and neutrinos, is handled
        # as a special case for efficiency
        if self._Tcmb0.value > 0:
            # Compute photon density from Tcmb
            self._Ogamma0 = a_B_c2 * self._Tcmb0.value ** 4 /\
                self._critical_density0.value

            # Compute Neutrino temperature
            # The constant in front is (4/11)^1/3 -- see any
            #  cosmology book for an explanation -- for example,
            #  Weinberg 'Cosmology' p 154 eq (3.1.21)
            self._Tnu0 = 0.7137658555036082 * self._Tcmb0

            # Compute Neutrino Omega and total relativistic component
            # for massive neutrinos
            if self._massivenu:
                nu_y = self._massivenu_mass / (kB_evK * self._Tnu0)
                self._nu_y = nu_y.value
                self._Onu0 = self._Ogamma0 * self.nu_relative_density(0)
            else:
                # This case is particularly simple, so do it directly
                # The 0.2271... is 7/8 (4/11)^(4/3) -- the temperature
                # bit ^4 (blackbody energy density) times 7/8 for
                # FD vs. BE statistics.
                self._Onu0 = 0.22710731766 * self._Neff * self._Ogamma0

        else:
            self._Ogamma0 = 0.0
            self._Tnu0 = u.Quantity(0.0, u.K)
            self._Onu0 = 0.0

        # Compute curvature density
        self._Ok0 = 1.0 - self._Om0 - self._Ode0 - self._Ogamma0 - self._Onu0

    def _namelead(self):
        """ Helper function for constructing __repr__"""
        if self.name is None:
            return "{0}(".format(self.__class__.__name__)
        else:
            return "{0}(name=\"{1}\", ".format(self.__class__.__name__,
                                               self.name)

    def __repr__(self):
        retstr = "{0}H0={1:.3g}, Om0={2:.3g}, Ode0={3:.3g}, "\
                 "Tcmb0={4:.4g}, Neff={5:.3g}, m_nu={6})"
        return retstr.format(self._namelead(), self._H0, self._Om0, self._Ode0,
                             self._Tcmb0, self._Neff, self.m_nu)

    # Set up a set of properties for H0, Om0, Ode0, Ok0, etc. for user access.
    # Note that we don't let these be set (so, obj.Om0 = value fails)

    @property
    def H0(self):
        """ Return the Hubble constant as an `~astropy.units.Quantity` at z=0"""
        return self._H0

    @property
    def Om0(self):
        """ Omega matter; matter density/critical density at z=0"""
        return self._Om0

    @property
    def Ode0(self):
        """ Omega dark energy; dark energy density/critical density at z=0"""
        return self._Ode0

    @property
    def Ok0(self):
        """ Omega curvature; the effective curvature density/critical density
        at z=0"""
        return self._Ok0

    @property
    def Tcmb0(self):
        """ Temperature of the CMB as `~astropy.units.Quantity` at z=0"""
        return self._Tcmb0

    @property
    def Tnu0(self):
        """ Temperature of the neutrino background as `~astropy.units.Quantity` at z=0"""
        return self._Tnu0

    @property
    def Neff(self):
        """ Number of effective neutrino species"""
        return self._Neff

    @property
    def has_massive_nu(self):
        """ Does this cosmology have at least one massive neutrino species?"""
        if self._Tnu0.value == 0:
            return False
        return self._massivenu

    @property
    def m_nu(self):
        """ Mass of neutrino species"""
        if self._Tnu0.value == 0:
            return None
        if not self._massivenu:
            # Only massless
            return u.Quantity(np.zeros(self._nmasslessnu), u.eV,
                              dtype=np.float)
        if self._nmasslessnu == 0:
            # Only massive
            return u.Quantity(self._massivenu_mass, u.eV,
                              dtype=np.float)
        # A mix -- the most complicated case
        numass = np.append(np.zeros(self._nmasslessnu),
                           self._massivenu_mass.value)
        return u.Quantity(numass, u.eV, dtype=np.float)

    @property
    def h(self):
        """ Dimensionless Hubble constant: h = H_0 / 100 [km/sec/Mpc]"""
        return self._h

    @property
    def hubble_time(self):
        """ Hubble time as `~astropy.units.Quantity`"""
        return self._hubble_time

    @property
    def hubble_distance(self):
        """ Hubble distance as `~astropy.units.Quantity`"""
        return self._hubble_distance

    @property
    def critical_density0(self):
        """ Critical density as `~astropy.units.Quantity` at z=0"""
        return self._critical_density0

    @property
    def Ogamma0(self):
        """ Omega gamma; the density/critical density of photons at z=0"""
        return self._Ogamma0

    @property
    def Onu0(self):
        """ Omega nu; the density/critical density of neutrinos at z=0"""
        return self._Onu0

    @abstractmethod
    def w(self, z):
        """ The dark energy equation of state.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        w : ndarray, or float if input scalar
          The dark energy equation of state

        Notes
        ------
        The dark energy equation of state is defined as
        :math:`w(z) = P(z)/\\rho(z)`, where :math:`P(z)` is the
        pressure at redshift z and :math:`\\rho(z)` is the density
        at redshift z, both in units where c=1.

        This must be overridden by subclasses.
        """
        raise NotImplementedError("w(z) is not implemented")

    def Om(self, z):
        """ 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.
        """

        if isiterable(z):
            z = np.asarray(z)
        return self._Om0 * (1. + z) ** 3 * self.inv_efunc(z) ** 2

    def Ok(self, z):
        """ Return the equivalent density parameter for curvature
        at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        Ok : ndarray, or float if input scalar
          The equivalent density parameter for curvature at each redshift.
        """

        if isiterable(z):
            z = np.asarray(z)
            # Common enough case to be worth checking explicitly
            if self._Ok0 == 0:
                return np.zeros(np.asanyarray(z).shape, dtype=np.float)
        else:
            if self._Ok0 == 0:
                return 0.0

        return self._Ok0 * (1. + z) ** 2 * self.inv_efunc(z) ** 2

    def Ode(self, z):
        """ Return the density parameter for dark energy at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        Ode : ndarray, or float if input scalar
          The density of non-relativistic matter relative to the critical
          density at each redshift.
        """

        if isiterable(z):
            z = np.asarray(z)
            # Common case worth checking
            if self._Ode0 == 0:
                return np.zeros(np.asanyarray(z).shape, dtype=np.float)
        else:
            if self._Ode0 == 0:
                return 0.0

        return self._Ode0 * self.de_density_scale(z) * self.inv_efunc(z) ** 2

    def Ogamma(self, z):
        """ Return the density parameter for photons at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        Ogamma : ndarray, or float if input scalar
          The energy density of photons relative to the critical
          density at each redshift.
        """

        if isiterable(z):
            z = np.asarray(z)
        return self._Ogamma0 * (1. + z) ** 4 * self.inv_efunc(z) ** 2

    def Onu(self, z):
        """ Return the density parameter for massless neutrinos at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        Onu : ndarray, or float if input scalar
          The energy density of photons 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.
        """

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

        return self.Ogamma(z) * self.nu_relative_density(z)

    def Tcmb(self, z):
        """ Return the CMB temperature at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        Tcmb : `~astropy.units.Quantity`
          The temperature of the CMB in K.
        """

        if isiterable(z):
            z = np.asarray(z)
        return self._Tcmb0 * (1. + z)

    def Tnu(self, z):
        """ Return the neutrino temperature at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        Tnu : `~astropy.units.Quantity`
          The temperature of the cosmic neutrino background in K.
        """

        if isiterable(z):
            z = np.asarray(z)
        return self._Tnu0 * (1. + z)

    def nu_relative_density(self, z):
        """ Neutrino density function relative to the energy density in
        photons.

        Parameters
        ----------
        z : array like
           Redshift

        Returns
        -------
         f : ndarray, or float if z is scalar
           The neutrino density scaling factor relative to the density
           in photons at each redshift

        Notes
        -----
        The density in neutrinos is given by

        .. math::

          \\rho_{\\nu} \\left(a\\right) = 0.2271 \\, N_{eff} \\,
          f\\left(m_{\\nu} a / T_{\\nu 0} \\right) \\,
          \\rho_{\\gamma} \\left( a \\right)

        where

        .. math::

          f \\left(y\\right) = \\frac{120}{7 \\pi^4}
          \\int_0^{\\infty} \\, dx \\frac{x^2 \\sqrt{x^2 + y^2}}
          {e^x + 1}

        assuming that all neutrino species have the same mass.
        If they have different masses, a similar term is calculated
        for each one. Note that f has the asymptotic behavior :math:`f(0) = 1`.
        This method returns :math:`0.2271 f` using an
        analytical fitting formula given in Komatsu et al. 2011, ApJS 192, 18.
        """

        # See Komatsu et al. 2011, eq 26 and the surrounding discussion
        # However, this is modified to handle multiple neutrino masses
        # by computing the above for each mass, then summing
        prefac = 0.22710731766  # 7/8 (4/11)^4/3 -- see any cosmo book

        # The massive and massless contribution must be handled seperately
        # But check for common cases first
        if not self._massivenu:
            if np.isscalar(z):
                return prefac * self._Neff
            else:
                return prefac * self._Neff *\
                    np.ones(np.asanyarray(z).shape, dtype=np.float)

        p = 1.83
        invp = 1.0 / p
        if np.isscalar(z):
            curr_nu_y = self._nu_y / (1.0 + z)  # only includes massive ones
            rel_mass_per = (1.0 + (0.3173 * curr_nu_y) ** p) ** invp
            rel_mass = rel_mass_per.sum() + self._nmasslessnu
        else:
            z = np.asarray(z)
            retarr = np.empty_like(z)
            curr_nu_y = self._nu_y / (1. + np.expand_dims(z, axis=-1))
            rel_mass_per = (1. + (0.3173 * curr_nu_y) ** p) ** invp
            rel_mass = rel_mass_per.sum(-1) + self._nmasslessnu

        return prefac * self._neff_per_nu * rel_mass

    def _w_integrand(self, ln1pz):
        """ Internal convenience function for w(z) integral."""

        # See Linder 2003, PRL 90, 91301 eq (5)
        # Assumes scalar input, since this should only be called
        # inside an integral

        z = exp(ln1pz) - 1.0
        return 1.0 + self.w(z)

    def de_density_scale(self, z):
        """ 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 is given by

        .. math::

            I = \\exp \\left( 3 \int_{a}^1 \\frac{ da^{\\prime} }{ a^{\\prime} }
            \\left[ 1 + w\\left( a^{\\prime} \\right) \\right] \\right)

        It will generally helpful for subclasses to overload this method if
        the integral can be done analytically for the particular dark
        energy equation of state that they implement.
        """

        # This allows for an arbitrary w(z) following eq (5) of
        # Linder 2003, PRL 90, 91301.  The code here evaluates
        # the integral numerically.  However, most popular
        # forms of w(z) are designed to make this integral analytic,
        # so it is probably a good idea for subclasses to overload this
        # method if an analytic form is available.
        #
        # The integral we actually use (the one given in Linder)
        # is rewritten in terms of z, so looks slightly different than the
        # one in the documentation string, but it's the same thing.

        from scipy.integrate import quad

        if isiterable(z):
            z = np.asarray(z)
            ival = np.array([quad(self._w_integrand, 0, log(1 + redshift))[0]
                             for redshift in z])
            return np.exp(3 * ival)
        else:
            ival = quad(self._w_integrand, 0, log(1 + z))[0]
            return exp(3 * ival)

    def efunc(self, z):
        """ Function used to calculate H(z), the Hubble parameter.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        E : ndarray, or float if input scalar
          The redshift scaling of the Hubble constant.

        Notes
        -----
        The return value, E, is defined such that :math:`H(z) = H_0 E`.

        It is not necessary to override this method, but if de_density_scale
        takes a particularly simple form, it may be advantageous to.
        """

        if isiterable(z):
            z = np.asarray(z)

        Om0, Ode0, Ok0 = self._Om0, self._Ode0, self._Ok0
        if self._massivenu:
            Or = self._Ogamma0 * (1 + self.nu_relative_density(z))
        else:
            Or = self._Ogamma0 + self._Onu0
        zp1 = 1.0 + z

        return np.sqrt(zp1 ** 2 * ((Or * zp1 + Om0) * zp1 + Ok0) +
                       Ode0 * self.de_density_scale(z))

    def inv_efunc(self, z):
        """Inverse of efunc.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        E : ndarray, or float if input scalar
          The redshift scaling of the inverse Hubble constant.
        """

        # Avoid the function overhead by repeating code
        if isiterable(z):
            z = np.asarray(z)
        Om0, Ode0, Ok0 = self._Om0, self._Ode0, self._Ok0
        if self._massivenu:
            Or = self._Ogamma0 * (1 + self.nu_relative_density(z))
        else:
            Or = self._Ogamma0 + self._Onu0
        zp1 = 1.0 + z

        return 1.0 / np.sqrt(zp1 ** 2 * ((Or * zp1 + Om0) * zp1 + Ok0) +
                             Ode0 * self.de_density_scale(z))

    def _tfunc(self, z):
        """ Integrand of the lookback time.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        I : ndarray, or float if input scalar
          The integrand for the lookback time

        References
        ----------
        Eqn 30 from Hogg 1999.
        """

        if isiterable(z):
            zp1 = 1.0 + np.asarray(z)
        else:
            zp1 = 1. + z

        return 1.0 / (zp1 * self.efunc(z))

    def _xfunc(self, z):
        """ Integrand of the absorption distance.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        X : ndarray, or float if input scalar
          The integrand for the absorption distance

        References
        ----------
        See Hogg 1999 section 11.
        """

        if isiterable(z):
            zp1 = 1.0 + np.asarray(z)
        else:
            zp1 = 1. + z
        return zp1 ** 2 / self.efunc(z)

    def H(self, z):
        """ Hubble parameter (km/s/Mpc) at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        H : `~astropy.units.Quantity`
          Hubble parameter at each input redshift.
        """

        return self._H0 * self.efunc(z)

    def scale_factor(self, z):
        """ 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.
        """

        if isiterable(z):
            z = np.asarray(z)

        return 1. / (1. + z)

    def lookback_time(self, z):
        """ Lookback time in Gyr to redshift ``z``.

        The lookback time is the difference between the age of the
        Universe now and the age at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar

        Returns
        -------
        t : `~astropy.units.Quantity`
          Lookback time in Gyr to each input redshift.

        See Also
        --------
        z_at_value : Find the redshift corresponding to a lookback time.
        """

        from scipy.integrate import quad
        if not isiterable(z):
            return self._hubble_time * quad(self._tfunc, 0, z)[0]

        out = np.array([quad(self._tfunc, 0, redshift)[0] for redshift in z])
        return self._hubble_time * np.array(out)

    def age(self, z):
        """ Age of the universe in Gyr at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        t : `~astropy.units.Quantity`
          The age of the universe in Gyr at each input redshift.

        See Also
        --------
        z_at_value : Find the redshift corresponding to an age.
        """

        from scipy.integrate import quad
        if not isiterable(z):
            return self._hubble_time * quad(self._tfunc, z, np.inf)[0]

        out = [quad(self._tfunc, redshift, np.inf)[0] for redshift in z]
        return self._hubble_time * np.array(out)

    def critical_density(self, z):
        """ Critical density in grams per cubic cm at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        rho : `~astropy.units.Quantity`
          Critical density in g/cm^3 at each input redshift.
        """

        return self._critical_density0 * (self.efunc(z)) ** 2

    def comoving_distance(self, z):
        """ Comoving line-of-sight distance in Mpc at a given
        redshift.

        The comoving distance along the line-of-sight between two
        objects remains constant with time for objects in the Hubble
        flow.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        d : ndarray, or float if input scalar
          Comoving distance in Mpc to each input redshift.
        """

        from scipy.integrate import quad
        if not isiterable(z):
            return self._hubble_distance * quad(self.inv_efunc, 0, z)[0]

        out = [quad(self.inv_efunc, 0, redshift)[0] for redshift in z]
        return self._hubble_distance * np.array(out)

    def comoving_transverse_distance(self, z):
        """ Comoving transverse distance in Mpc at a given redshift.

        This value is the transverse comoving distance at redshift ``z``
        corresponding to an angular separation of 1 radian. This is
        the same as the comoving distance if omega_k is zero (as in
        the current concordance lambda CDM model).

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        d : `~astropy.units.Quantity`
          Comoving transverse distance in Mpc at each input redshift.

        Notes
        -----
        This quantity also called the 'proper motion distance' in some
        texts.
        """

        Ok0 = self._Ok0
        dc = self.comoving_distance(z)
        if Ok0 == 0:
            return dc
        sqrtOk0 = sqrt(abs(Ok0))
        dh = self._hubble_distance
        if Ok0 > 0:
            return dh / sqrtOk0 * np.sinh(sqrtOk0 * dc.value / dh.value)
        else:
            return dh / sqrtOk0 * np.sin(sqrtOk0 * dc.value / dh.value)

    def angular_diameter_distance(self, z):
        """ Angular diameter distance in Mpc at a given redshift.

        This gives the proper (sometimes called 'physical') transverse
        distance corresponding to an angle of 1 radian for an object
        at redshift ``z``.

        Weinberg, 1972, pp 421-424; Weedman, 1986, pp 65-67; Peebles,
        1993, pp 325-327.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        d : `~astropy.units.Quantity`
          Angular diameter distance in Mpc at each input redshift.
        """

        if isiterable(z):
            z = np.asarray(z)

        return self.comoving_transverse_distance(z) / (1. + z)

    def luminosity_distance(self, z):
        """ Luminosity distance in Mpc at redshift ``z``.

        This is the distance to use when converting between the
        bolometric flux from an object at redshift ``z`` and its
        bolometric luminosity.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        d : `~astropy.units.Quantity`
          Luminosity distance in Mpc at each input redshift.

        See Also
        --------
        z_at_value : Find the redshift corresponding to a luminosity distance.

        References
        ----------
        Weinberg, 1972, pp 420-424; Weedman, 1986, pp 60-62.
        """

        if isiterable(z):
            z = np.asarray(z)

        return (1. + z) * self.comoving_transverse_distance(z)

    def angular_diameter_distance_z1z2(self, z1, z2):
        """ Angular diameter distance between objects at 2 redshifts.
        Useful for gravitational lensing.

        Parameters
        ----------
        z1, z2 : array_like, shape (N,)
          Input redshifts. z2 must be large than z1.

        Returns
        -------
        d : `~astropy.units.Quantity`, shape (N,) or single if input scalar
          The angular diameter distance between each input redshift
          pair.

        Raises
        ------
        CosmologyError
          If omega_k is < 0.

        Notes
        -----
        This method only works for flat or open curvature
        (omega_k >= 0).
        """

        # does not work for negative curvature
        Ok0 = self._Ok0
        if Ok0 < 0:
            raise CosmologyError('Ok0 must be >= 0 to use this method.')

        outscalar = False
        if not isiterable(z1) and not isiterable(z2):
            outscalar = True

        z1 = np.atleast_1d(z1)
        z2 = np.atleast_1d(z2)

        if z1.size != z2.size:
            raise ValueError('z1 and z2 must be the same size.')

        if (z1 > z2).any():
            raise ValueError('z2 must greater than z1')

        # z1 < z2
        if (z2 < z1).any():
            z1, z2 = z2, z1

        dm1 = self.comoving_transverse_distance(z1).value
        dm2 = self.comoving_transverse_distance(z2).value
        dh_2 = self._hubble_distance.value ** 2

        if Ok0 == 0:
            # Common case worth checking
            out = (dm2 - dm1) / (1. + z2)
        else:
            out = ((dm2 * np.sqrt(1. + Ok0 * dm1 ** 2 / dh_2) -
                    dm1 * np.sqrt(1. + Ok0 * dm2 ** 2 / dh_2)) /
                   (1. + z2))

        if outscalar:
            return u.Quantity(out[0], u.Mpc)

        return u.Quantity(out, u.Mpc)

    def absorption_distance(self, z):
        """ Absorption distance at redshift ``z``.

        This is used to calculate the number of objects with some
        cross section of absorption and number density intersecting a
        sightline per unit redshift path.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        d : float or ndarray
          Absorption distance (dimensionless) at each input redshift.

        References
        ----------
        Hogg 1999 Section 11. (astro-ph/9905116)
        Bahcall, John N. and Peebles, P.J.E. 1969, ApJ, 156L, 7B
        """

        from scipy.integrate import quad
        if not isiterable(z):
            return quad(self._xfunc, 0, z)[0]

        out = np.array([quad(self._xfunc, 0, redshift)[0] for redshift in z])
        return out

    def distmod(self, z):
        """ Distance modulus at redshift ``z``.

        The distance modulus is defined as the (apparent magnitude -
        absolute magnitude) for an object at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        distmod : `~astropy.units.Quantity`
          Distance modulus at each input redshift, in magnitudes

        See Also
        --------
        z_at_value : Find the redshift corresponding to a distance modulus.
        """

        # Remember that the luminosity distance is in Mpc
        # Abs is necessary because in certain obscure closed cosmologies
        #  the distance modulus can be negative -- which is okay because
        #  it enters as the square.
        val = 5. * np.log10(abs(self.luminosity_distance(z).value)) + 25.0
        return u.Quantity(val, u.mag)

    def comoving_volume(self, z):
        """ Comoving volume in cubic Mpc at redshift ``z``.

        This is the volume of the universe encompassed by redshifts less
        than ``z``. For the case of omega_k = 0 it is a sphere of radius
        `comoving_distance` but it is less intuitive
        if omega_k is not 0.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        V : `~astropy.units.Quantity`
          Comoving volume in :math:`Mpc^3` at each input redshift.
        """

        Ok0 = self._Ok0
        if Ok0 == 0:
            return 4. / 3. * pi * self.comoving_distance(z) ** 3

        dh = self._hubble_distance.value  # .value for speed
        dm = self.comoving_transverse_distance(z).value
        term1 = 4. * pi * dh ** 3 / (2. * Ok0) * u.Mpc ** 3
        term2 = dm / dh * np.sqrt(1 + Ok0 * (dm / dh) ** 2)
        term3 = sqrt(abs(Ok0)) * dm / dh

        if Ok0 > 0:
            return term1 * (term2 - 1. / sqrt(abs(Ok0)) * np.arcsinh(term3))
        else:
            return term1 * (term2 - 1. / sqrt(abs(Ok0)) * np.arcsin(term3))

    def differential_comoving_volume(self, z):
        """Differential comoving volume at redshift z.

        Useful for calculating the effective comoving volume.
        For example, allows for integration over a comoving volume
        that has a sensitivity function that changes with redshift.
        The total comoving volume is given by integrating
        differential_comoving_volume to redshift z
        and multiplying by a solid angle.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        dV : `~astropy.units.Quantity`
          Differential comoving volume per redshift per steradian at
          each input redshift."""
        dh = self._hubble_distance
        da = self.angular_diameter_distance(z)
        zp1 = 1.0 + z
        return dh * (zp1 ** 2.0 * da ** 2.0) / u.Quantity(self.efunc(z),
                                                          u.steradian)

    def kpc_comoving_per_arcmin(self, z):
        """ Separation in transverse comoving kpc corresponding to an
        arcminute at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        d : `~astropy.units.Quantity`
          The distance in comoving kpc corresponding to an arcmin at each
          input redshift.
        """
        return (self.comoving_transverse_distance(z).to(u.kpc) *
                arcmin_in_radians / u.arcmin)

    def kpc_proper_per_arcmin(self, z):
        """ Separation in transverse proper kpc corresponding to an
        arcminute at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        d : `~astropy.units.Quantity`
          The distance in proper kpc corresponding to an arcmin at each
          input redshift.
        """
        return (self.angular_diameter_distance(z).to(u.kpc) *
                arcmin_in_radians / u.arcmin)

    def arcsec_per_kpc_comoving(self, z):
        """ Angular separation in arcsec corresponding to a comoving kpc
        at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        theta : `~astropy.units.Quantity`
          The angular separation in arcsec corresponding to a comoving kpc
          at each input redshift.
        """
        return u.arcsec / (self.comoving_transverse_distance(z).to(u.kpc) *
                           arcsec_in_radians)

    def arcsec_per_kpc_proper(self, z):
        """ Angular separation in arcsec corresponding to a proper kpc at
        redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.  Must be 1D or scalar.

        Returns
        -------
        theta : `~astropy.units.Quantity`
          The angular separation in arcsec corresponding to a proper kpc
          at each input redshift.
        """
        return u.arcsec / (self.angular_diameter_distance(z).to(u.kpc) *
                           arcsec_in_radians)


class LambdaCDM(FLRW):
    """FLRW cosmology with a cosmological constant and curvature.

    This has no additional attributes beyond those of FLRW.

    Parameters
    ----------

    H0 : float or `~astropy.units.Quantity`
        Hubble constant at z = 0.  If a float, must be in [km/sec/Mpc]

    Om0 : float
        Omega matter: density of non-relativistic matter in units of the
        critical density at z=0.

    Ode0 : float
        Omega dark energy: density of the cosmological constant in units of the
        critical density at z=0.

    Tcmb0 : float or `~astropy.units.Quantity`
        Temperature of the CMB z=0. If a float, must be in [K]. Default: 2.725.

    Neff : float
        Effective number of Neutrino species. Default 3.04.

    m_nu : `~astropy.units.Quantity`
        Mass of each neutrino species. If this is a scalar Quantity, then all
        neutrino species are assumed to have that mass. Otherwise, the mass of
        each species. The actual number of neutrino species (and hence the
        number of elements of m_nu if it is not scalar) must be the floor of
        Neff. Usually this means you must provide three neutrino masses unless
        you are considering something like a sterile neutrino.

    name : str
        Optional name for this cosmological object.

    Examples
    --------
    >>> from astropy.cosmology import LambdaCDM
    >>> cosmo = LambdaCDM(H0=70, Om0=0.3, Ode0=0.7)

    The comoving distance in Mpc at redshift z:

    >>> z = 0.5
    >>> dc = cosmo.comoving_distance(z)
    """

    def __init__(self, H0, Om0, Ode0, Tcmb0=2.725, Neff=3.04,
                 m_nu=u.Quantity(0.0, u.eV), name=None):

        FLRW.__init__(self, H0, Om0, Ode0, Tcmb0, Neff, m_nu, name=name)

    def w(self, z):
        """Returns dark energy equation of state at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        w : ndarray, or float if input scalar
          The dark energy equation of state

        Notes
        ------
        The dark energy equation of state is defined as
        :math:`w(z) = P(z)/\\rho(z)`, where :math:`P(z)` is the
        pressure at redshift z and :math:`\\rho(z)` is the density
        at redshift z, both in units where c=1.  Here this is
        :math:`w(z) = -1`.
        """

        if np.isscalar(z):
            return -1.0
        else:
            return -1.0 * np.ones(np.asanyarray(z).shape, dtype=np.float)

    def de_density_scale(self, z):
        """ 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 = 1`.
        """

        if np.isscalar(z):
            return 1.
        else:
            return np.ones(np.asanyarray(z).shape, dtype=np.float)

    def efunc(self, z):
        """ Function used to calculate H(z), the Hubble parameter.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        E : ndarray, or float if input scalar
          The redshift scaling of the Hubble consant.

        Notes
        -----
        The return value, E, is defined such that :math:`H(z) = H_0 E`.
        """

        if isiterable(z):
            z = np.asarray(z)

        # We override this because it takes a particularly simple
        # form for a cosmological constant
        Om0, Ode0, Ok0 = self._Om0, self._Ode0, self._Ok0
        if self._massivenu:
            Or = self._Ogamma0 * (1. + self.nu_relative_density(z))
        else:
            Or = self._Ogamma0 + self._Onu0
        zp1 = 1.0 + z

        return np.sqrt(zp1 ** 2 * ((Or * zp1 + Om0) * zp1 + Ok0) + Ode0)

    def inv_efunc(self, z):
        r""" Function used to calculate :math:`\frac{1}{H_z}`.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        E : ndarray, or float if input scalar
          The inverse redshift scaling of the Hubble constant.

        Notes
        -----
        The return value, E, is defined such that :math:`H_z = H_0 /
        E`.
        """

        if isiterable(z):
            z = np.asarray(z)
        Om0, Ode0, Ok0 = self._Om0, self._Ode0, self._Ok0
        if self._massivenu:
            Or = self._Ogamma0 * (1 + self.nu_relative_density(z))
        else:
            Or = self._Ogamma0 + self._Onu0
        zp1 = 1.0 + z

        return 1.0 / np.sqrt(zp1 ** 2 * ((Or * zp1 + Om0) * zp1 + Ok0) + Ode0)


class FlatLambdaCDM(LambdaCDM):
    """FLRW cosmology with a cosmological constant and no curvature.

    This has no additional attributes beyond those of FLRW.

    Parameters
    ----------
    H0 : float or `~astropy.units.Quantity`
        Hubble constant at z = 0.  If a float, must be in [km/sec/Mpc]

    Om0 : float
        Omega matter: density of non-relativistic matter in units of the
        critical density at z=0.

    Tcmb0 : float or `~astropy.units.Quantity`
        Temperature of the CMB z=0. If a float, must be in [K]. Default: 2.725.

    Neff : float
        Effective number of Neutrino species. Default 3.04.

    m_nu : `~astropy.units.Quantity`
        Mass of each neutrino species. If this is a scalar Quantity, then all
        neutrino species are assumed to have that mass. Otherwise, the mass of
        each species. The actual number of neutrino species (and hence the
        number of elements of m_nu if it is not scalar) must be the floor of
        Neff. Usually this means you must provide three neutrino masses unless
        you are considering something like a sterile neutrino.

    name : str
        Optional name for this cosmological object.

    Examples
    --------
    >>> from astropy.cosmology import FlatLambdaCDM
    >>> cosmo = FlatLambdaCDM(H0=70, Om0=0.3)

    The comoving distance in Mpc at redshift z:

    >>> z = 0.5
    >>> dc = cosmo.comoving_distance(z)
    """

    def __init__(self, H0, Om0, Tcmb0=2.725, Neff=3.04,
                 m_nu=u.Quantity(0.0, u.eV), name=None):

        FLRW.__init__(self, H0, Om0, 0.0, Tcmb0, Neff, m_nu, name=name)
        # Do some twiddling after the fact to get flatness
        self._Ode0 = 1.0 - self._Om0 - self._Ogamma0 - self._Onu0
        self._Ok0 = 0.0

    def efunc(self, z):
        """ Function used to calculate H(z), the Hubble parameter.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        E : ndarray, or float if input scalar
          The redshift scaling of the Hubble consant.

        Notes
        -----
        The return value, E, is defined such that :math:`H(z) = H_0 E`.
        """

        if isiterable(z):
            z = np.asarray(z)

        # We override this because it takes a particularly simple
        # form for a cosmological constant
        Om0, Ode0 = self._Om0, self._Ode0
        if self._massivenu:
            Or = self._Ogamma0 * (1 + self.nu_relative_density(z))
        else:
            Or = self._Ogamma0 + self._Onu0
        zp1 = 1.0 + z

        return np.sqrt(zp1 ** 3 * (Or * zp1 + Om0) + Ode0)

    def inv_efunc(self, z):
        r"""Function used to calculate :math:`\frac{1}{H_z}`.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        E : ndarray, or float if input scalar
          The inverse redshift scaling of the Hubble constant.

        Notes
        -----
        The return value, E, is defined such that :math:`H_z = H_0 / E`.
        """

        if isiterable(z):
            z = np.asarray(z)
        Om0, Ode0 = self._Om0, self._Ode0
        if self._massivenu:
            Or = self._Ogamma0 * (1. + self.nu_relative_density(z))
        else:
            Or = self._Ogamma0 + self._Onu0
        zp1 = 1.0 + z

        return 1.0 / np.sqrt(zp1 ** 3 * (Or * zp1 + Om0) + Ode0)

    def __repr__(self):
        retstr = "{0}H0={1:.3g}, Om0={2:.3g}, Tcmb0={3:.4g}, "\
                 "Neff={4:.3g}, m_nu={5})"
        return retstr.format(self._namelead(), self._H0, self._Om0,
                             self._Tcmb0, self._Neff, self.m_nu)


class wCDM(FLRW):
    """FLRW cosmology with a constant dark energy equation of state
    and curvature.

    This has one additional attribute beyond those of FLRW.

    Parameters
    ----------

    H0 : float or `~astropy.units.Quantity`
        Hubble constant at z = 0. If a float, must be in [km/sec/Mpc]

    Om0 : float
        Omega matter: density of non-relativistic matter in units of the
        critical density at z=0.

    Ode0 : float
        Omega dark energy: density of dark energy in units of the critical
        density at z=0.

    w0 : float
        Dark energy equation of state at all redshifts. This is
        pressure/density for dark energy in units where c=1. A cosmological
        constant has w0=-1.0.

    Tcmb0 : float or `~astropy.units.Quantity`
        Temperature of the CMB z=0. If a float, must be in [K]. Default: 2.725.

    Neff : float
        Effective number of Neutrino species. Default 3.04.

    m_nu : `~astropy.units.Quantity`
        Mass of each neutrino species. If this is a scalar Quantity, then all
        neutrino species are assumed to have that mass. Otherwise, the mass of
        each species. The actual number of neutrino species (and hence the
        number of elements of m_nu if it is not scalar) must be the floor of
        Neff. Usually this means you must provide three neutrino masses unless
        you are considering something like a sterile neutrino.

    name : str
        Optional name for this cosmological object.

    Examples
    --------
    >>> from astropy.cosmology import wCDM
    >>> cosmo = wCDM(H0=70, Om0=0.3, Ode0=0.7, w0=-0.9)

    The comoving distance in Mpc at redshift z:

    >>> z = 0.5
    >>> dc = cosmo.comoving_distance(z)
    """

    def __init__(self, H0, Om0, Ode0, w0=-1., Tcmb0=2.725,
                 Neff=3.04, m_nu=u.Quantity(0.0, u.eV), name=None):

        FLRW.__init__(self, H0, Om0, Ode0, Tcmb0, Neff, m_nu, name=name)
        self._w0 = float(w0)

    @property
    def w0(self):
        """ Dark energy equation of state"""
        return self._w0

    def w(self, z):
        """Returns dark energy equation of state at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        w : ndarray, or float if input scalar
          The dark energy equation of state

        Notes
        ------
        The dark energy equation of state is defined as
        :math:`w(z) = P(z)/\\rho(z)`, where :math:`P(z)` is the
        pressure at redshift z and :math:`\\rho(z)` is the density
        at redshift z, both in units where c=1.  Here this is
        :math:`w(z) = w_0`.
        """

        if np.isscalar(z):
            return self._w0
        else:
            return self._w0 * np.ones(np.asanyarray(z).shape, dtype=np.float)

    def de_density_scale(self, z):
        """ 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)}`
        """

        if isiterable(z):
            z = np.asarray(z)
        return (1. + z) ** (3. * (1. + self._w0))

    def efunc(self, z):
        """ Function used to calculate H(z), the Hubble parameter.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        E : ndarray, or float if input scalar
          The redshift scaling of the Hubble consant.

        Notes
        -----
        The return value, E, is defined such that :math:`H(z) = H_0 E`.
        """

        if isiterable(z):
            z = np.asarray(z)
        Om0, Ode0, Ok0, w0 = self._Om0, self._Ode0, self._Ok0, self._w0
        if self._massivenu:
            Or = self._Ogamma0 * (1. + self.nu_relative_density(z))
        else:
            Or = self._Ogamma0 + self._Onu0
        zp1 = 1.0 + z

        return np.sqrt(zp1 ** 2 * ((Or * zp1 + Om0) * zp1 + Ok0) +
                       Ode0 * zp1 ** (3. * (1. + w0)))

    def inv_efunc(self, z):
        r""" Function used to calculate :math:`\frac{1}{H_z}`.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        E : ndarray, or float if input scalar
          The inverse redshift scaling of the Hubble constant.

        Notes
        -----
        The return value, E, is defined such that :math:`H_z = H_0 / E`.
        """

        if isiterable(z):
            z = np.asarray(z)
        Om0, Ode0, Ok0, w0 = self._Om0, self._Ode0, self._Ok0, self._w0
        if self._massivenu:
            Or = self._Ogamma0 * (1. + self.nu_relative_density(z))
        else:
            Or = self._Ogamma0 + self._Onu0
        zp1 = 1.0 + z

        return 1.0 / np.sqrt(zp1 ** 2 * ((Or * zp1 + Om0) * zp1 + Ok0) +
                             Ode0 * zp1 ** (3. * (1. + w0)))

    def __repr__(self):
        retstr = "{0}H0={1:.3g}, Om0={2:.3g}, Ode0={3:.3g}, w0={4:.3g}, "\
                 "Tcmb0={5:.4g}, Neff={6:.3g}, m_nu={7})"
        return retstr.format(self._namelead(), self._H0, self._Om0,
                             self._Ode0, self._w0, self._Tcmb0, self._Neff,
                             self.m_nu)


class FlatwCDM(wCDM):
    """FLRW cosmology with a constant dark energy equation of state
    and no spatial curvature.

    This has one additional attribute beyond those of FLRW.

    Parameters
    ----------

    H0 : float or `~astropy.units.Quantity`
        Hubble constant at z = 0. If a float, must be in [km/sec/Mpc]

    Om0 : float
        Omega matter: density of non-relativistic matter in units of the
        critical density at z=0.

    w0 : float
        Dark energy equation of state at all redshifts. This is
        pressure/density for dark energy in units where c=1. A cosmological
        constant has w0=-1.0.

    Tcmb0 : float or `~astropy.units.Quantity`
        Temperature of the CMB z=0. If a float, must be in [K]. Default: 2.725.

    Neff : float
        Effective number of Neutrino species. Default 3.04.

    m_nu : `~astropy.units.Quantity`
        Mass of each neutrino species. If this is a scalar Quantity, then all
        neutrino species are assumed to have that mass. Otherwise, the mass of
        each species. The actual number of neutrino species (and hence the
        number of elements of m_nu if it is not scalar) must be the floor of
        Neff. Usually this means you must provide three neutrino masses unless
        you are considering something like a sterile neutrino.

    name : str
        Optional name for this cosmological object.

    Examples
    --------
    >>> from astropy.cosmology import FlatwCDM
    >>> cosmo = FlatwCDM(H0=70, Om0=0.3, w0=-0.9)

    The comoving distance in Mpc at redshift z:

    >>> z = 0.5
    >>> dc = cosmo.comoving_distance(z)
    """

    def __init__(self, H0, Om0, w0=-1., Tcmb0=2.725,
                 Neff=3.04, m_nu=u.Quantity(0.0, u.eV), name=None):

        FLRW.__init__(self, H0, Om0, 0.0, Tcmb0, Neff, m_nu, name=name)
        self._w0 = float(w0)
        # Do some twiddling after the fact to get flatness
        self._Ode0 = 1.0 - self._Om0 - self._Ogamma0 - self._Onu0
        self._Ok0 = 0.0

    def efunc(self, z):
        """ Function used to calculate H(z), the Hubble parameter.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        E : ndarray, or float if input scalar
          The redshift scaling of the Hubble consant.

        Notes
        -----
        The return value, E, is defined such that :math:`H(z) = H_0 E`.
        """

        if isiterable(z):
            z = np.asarray(z)
        Om0, Ode0, w0 = self._Om0, self._Ode0, self._w0
        if self._massivenu:
            Or = self._Ogamma0 * (1. + self.nu_relative_density(z))
        else:
            Or = self._Ogamma0 + self._Onu0
        zp1 = 1. + z

        return np.sqrt(zp1 ** 3 * (Or * zp1 + Om0) +
                       Ode0 * zp1 ** (3. * (1 + w0)))

    def inv_efunc(self, z):
        r""" Function used to calculate :math:`\frac{1}{H_z}`.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        E : ndarray, or float if input scalar
          The inverse redshift scaling of the Hubble constant.

        Notes
        -----
        The return value, E, is defined such that :math:`H_z = H_0 / E`.
        """

        if isiterable(z):
            z = np.asarray(z)
        Om0, Ode0, Ok0, w0 = self._Om0, self._Ode0, self._Ok0, self._w0
        if self._massivenu:
            Or = self._Ogamma0 * (1. + self.nu_relative_density(z))
        else:
            Or = self._Ogamma0 + self._Onu0
        zp1 = 1. + z

        return 1. / np.sqrt(zp1 ** 3 * (Or * zp1 + Om0) +
                            Ode0 * zp1 ** (3. * (1. + w0)))

    def __repr__(self):
        retstr = "{0}H0={1:.3g}, Om0={2:.3g}, w0={3:.3g}, Tcmb0={4:.4g}, "\
                 "Neff={5:.3g}, m_nu={6})"
        return retstr.format(self._namelead(), self._H0, self._Om0, self._w0,
                             self._Tcmb0, self._Neff, self.m_nu)


class w0waCDM(FLRW):
    """FLRW cosmology with a CPL dark energy equation of state and curvature.

    The equation for the dark energy equation of state uses the
    CPL form as described in Chevallier & Polarski Int. J. Mod. Phys.
    D10, 213 (2001) and Linder PRL 90, 91301 (2003):
    :math:`w(z) = w_0 + w_a (1-a) = w_0 + w_a z / (1+z)`.

    Parameters
    ----------
    H0 : float or `~astropy.units.Quantity`
        Hubble constant at z = 0. If a float, must be in [km/sec/Mpc]

    Om0 : float
        Omega matter: density of non-relativistic matter in units of the
        critical density at z=0.

    Ode0 : float
        Omega dark energy: density of dark energy in units of the critical
        density at z=0.

    w0 : float
        Dark energy equation of state at z=0 (a=1). This is pressure/density
        for dark energy in units where c=1.

    wa : float
        Negative derivative of the dark energy equation of state with respect
        to the scale factor. A cosmological constant has w0=-1.0 and wa=0.0.

    Tcmb0 : float or `~astropy.units.Quantity`
        Temperature of the CMB z=0. If a float, must be in [K]. Default: 2.725.

    Neff : float
        Effective number of Neutrino species. Default 3.04.

    m_nu : `~astropy.units.Quantity`
        Mass of each neutrino species. If this is a scalar Quantity, then all
        neutrino species are assumed to have that mass. Otherwise, the mass of
        each species. The actual number of neutrino species (and hence the
        number of elements of m_nu if it is not scalar) must be the floor of
        Neff. Usually this means you must provide three neutrino masses unless
        you are considering something like a sterile neutrino.

    name : str
        Optional name for this cosmological object.

    Examples
    --------
    >>> from astropy.cosmology import w0waCDM
    >>> cosmo = w0waCDM(H0=70, Om0=0.3, Ode0=0.7, w0=-0.9, wa=0.2)

    The comoving distance in Mpc at redshift z:

    >>> z = 0.5
    >>> dc = cosmo.comoving_distance(z)
    """

    def __init__(self, H0, Om0, Ode0, w0=-1., wa=0., Tcmb0=2.725,
                 Neff=3.04, m_nu=u.Quantity(0.0, u.eV), name=None):

        FLRW.__init__(self, H0, Om0, Ode0, Tcmb0, Neff, m_nu, name=name)
        self._w0 = float(w0)
        self._wa = float(wa)

    @property
    def w0(self):
        """ Dark energy equation of state at z=0"""
        return self._w0

    @property
    def wa(self):
        """ Negative derivative of dark energy equation of state w.r.t. a"""
        return self._wa

    def w(self, z):
        """Returns dark energy equation of state at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        w : ndarray, or float if input scalar
          The dark energy equation of state

        Notes
        ------
        The dark energy equation of state is defined as
        :math:`w(z) = P(z)/\\rho(z)`, where :math:`P(z)` is the
        pressure at redshift z and :math:`\\rho(z)` is the density
        at redshift z, both in units where c=1.  Here this is
        :math:`w(z) = w_0 + w_a (1 - a) = w_0 + w_a \\frac{z}{1+z}`.
        """

        if isiterable(z):
            z = np.asarray(z)

        return self._w0 + self._wa * z / (1.0 + z)

    def de_density_scale(self, z):
        """ 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_a\\right)}
          \exp \\left(-3 w_a \\frac{z}{1+z}\\right)

        """
        if isiterable(z):
            z = np.asarray(z)
        zp1 = 1.0 + z
        return zp1 ** (3 * (1 + self._w0 + self._wa)) * \
            np.exp(-3 * self._wa * z / zp1)

    def __repr__(self):
        retstr = "{0}H0={1:.3g}, Om0={2:.3g}, "\
                 "Ode0={3:.3g}, w0={4:.3g}, wa={5:.3g}, Tcmb0={6:.4g}, "\
                 "Neff={7:.3g}, m_nu={8})"
        return retstr.format(self._namelead(), self._H0, self._Om0,
                             self._Ode0, self._w0, self._wa,
                             self._Tcmb0, self._Neff, self.m_nu)


class Flatw0waCDM(w0waCDM):
    """FLRW cosmology with a CPL dark energy equation of state and no curvature.

    The equation for the dark energy equation of state uses the
    CPL form as described in Chevallier & Polarski Int. J. Mod. Phys.
    D10, 213 (2001) and Linder PRL 90, 91301 (2003):
    :math:`w(z) = w_0 + w_a (1-a) = w_0 + w_a z / (1+z)`.

    Parameters
    ----------

    H0 : float or `~astropy.units.Quantity`
        Hubble constant at z = 0. If a float, must be in [km/sec/Mpc]

    Om0 : float
        Omega matter: density of non-relativistic matter in units of the
        critical density at z=0.

    w0 : float
        Dark energy equation of state at z=0 (a=1). This is pressure/density
        for dark energy in units where c=1.

    wa : float
        Negative derivative of the dark energy equation of state with respect
        to the scale factor. A cosmological constant has w0=-1.0 and wa=0.0.

    Tcmb0 : float or `~astropy.units.Quantity`
        Temperature of the CMB z=0. If a float, must be in [K]. Default: 2.725.

    Neff : float
        Effective number of Neutrino species. Default 3.04.

    m_nu : `~astropy.units.Quantity`
        Mass of each neutrino species. If this is a scalar Quantity, then all
        neutrino species are assumed to have that mass. Otherwise, the mass of
        each species. The actual number of neutrino species (and hence the
        number of elements of m_nu if it is not scalar) must be the floor of
        Neff. Usually this means you must provide three neutrino masses unless
        you are considering something like a sterile neutrino.

    name : str
        Optional name for this cosmological object.

    Examples
    --------
    >>> from astropy.cosmology import Flatw0waCDM
    >>> cosmo = Flatw0waCDM(H0=70, Om0=0.3, w0=-0.9, wa=0.2)

    The comoving distance in Mpc at redshift z:

    >>> z = 0.5
    >>> dc = cosmo.comoving_distance(z)
    """

    def __init__(self, H0, Om0, w0=-1., wa=0., Tcmb0=2.725,
                 Neff=3.04, m_nu=u.Quantity(0.0, u.eV), name=None):

        FLRW.__init__(self, H0, Om0, 0.0, Tcmb0, Neff, m_nu, name=name)
        # Do some twiddling after the fact to get flatness
        self._Ode0 = 1.0 - self._Om0 - self._Ogamma0 - self._Onu0
        self._Ok0 = 0.0
        self._w0 = float(w0)
        self._wa = float(wa)

    def __repr__(self):
        retstr = "{0}H0={1:.3g}, Om0={2:.3g}, "\
                 "w0={3:.3g}, Tcmb0={4:.4g}, Neff={5:.3g}, m_nu={6})"
        return retstr.format(self._namelead(), self._H0, self._Om0, self._w0,
                             self._Tcmb0, self._Neff, self.m_nu)


class wpwaCDM(FLRW):
    """FLRW cosmology with a CPL dark energy equation of state, a pivot
    redshift, and curvature.

    The equation for the dark energy equation of state uses the
    CPL form as described in Chevallier & Polarski Int. J. Mod. Phys.
    D10, 213 (2001) and Linder PRL 90, 91301 (2003), but modified
    to have a pivot redshift as in the findings of the Dark Energy
    Task Force (Albrecht et al. arXiv:0901.0721 (2009)):
    :math:`w(a) = w_p + w_a (a_p - a) = w_p + w_a( 1/(1+zp) - 1/(1+z) )`.

    Parameters
    ----------

    H0 : float or `~astropy.units.Quantity`
        Hubble constant at z = 0. If a float, must be in [km/sec/Mpc]

    Om0 : float
        Omega matter: density of non-relativistic matter in units of the
        critical density at z=0.

    Ode0 : float
        Omega dark energy: density of dark energy in units of the critical
        density at z=0.

    wp : float
        Dark energy equation of state at the pivot redshift zp. This is
        pressure/density for dark energy in units where c=1.

    wa : float
        Negative derivative of the dark energy equation of state with respect
        to the scale factor. A cosmological constant has w0=-1.0 and wa=0.0.

    zp : float
        Pivot redshift -- the redshift where w(z) = wp

    Tcmb0 : float or `~astropy.units.Quantity`
        Temperature of the CMB z=0. If a float, must be in [K]. Default: 2.725.

    Neff : float
        Effective number of Neutrino species. Default 3.04.

    m_nu : `~astropy.units.Quantity`
        Mass of each neutrino species. If this is a scalar Quantity, then all
        neutrino species are assumed to have that mass. Otherwise, the mass of
        each species. The actual number of neutrino species (and hence the
        number of elements of m_nu if it is not scalar) must be the floor of
        Neff. Usually this means you must provide three neutrino masses unless
        you are considering something like a sterile neutrino.

    name : str
        Optional name for this cosmological object.

    Examples
    --------
    >>> from astropy.cosmology import wpwaCDM
    >>> cosmo = wpwaCDM(H0=70, Om0=0.3, Ode0=0.7, wp=-0.9, wa=0.2, zp=0.4)

    The comoving distance in Mpc at redshift z:

    >>> z = 0.5
    >>> dc = cosmo.comoving_distance(z)
    """

    def __init__(self, H0, Om0, Ode0, wp=-1., wa=0., zp=0,
                 Tcmb0=2.725, Neff=3.04, m_nu=u.Quantity(0.0, u.eV),
                 name=None):

        FLRW.__init__(self, H0, Om0, Ode0, Tcmb0, Neff, m_nu, name=name)
        self._wp = float(wp)
        self._wa = float(wa)
        self._zp = float(zp)

    @property
    def wp(self):
        """ Dark energy equation of state at the pivot redshift zp"""
        return self._wp

    @property
    def wa(self):
        """ Negative derivative of dark energy equation of state w.r.t. a"""
        return self._wa

    @property
    def zp(self):
        """ The pivot redshift, where w(z) = wp"""
        return self._zp

    def w(self, z):
        """Returns dark energy equation of state at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        w : ndarray, or float if input scalar
          The dark energy equation of state

        Notes
        ------
        The dark energy equation of state is defined as
        :math:`w(z) = P(z)/\\rho(z)`, where :math:`P(z)` is the
        pressure at redshift z and :math:`\\rho(z)` is the density
        at redshift z, both in units where c=1.  Here this is
        :math:`w(z) = w_p + w_a (a_p - a)` where :math:`a = 1/1+z`
        and :math:`a_p = 1 / 1 + z_p`.
        """

        if isiterable(z):
            z = np.asarray(z)

        apiv = 1.0 / (1.0 + self._zp)
        return self._wp + self._wa * (apiv - 1.0 / (1. + z))

    def de_density_scale(self, z):
        """ 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::

          a_p = \\frac{1}{1 + z_p}

          I = \\left(1 + z\\right)^{3 \\left(1 + w_p + a_p w_a\\right)}
          \exp \\left(-3 w_a \\frac{z}{1+z}\\right)
        """

        if isiterable(z):
            z = np.asarray(z)
        zp1 = 1. + z
        apiv = 1. / (1. + self._zp)
        return zp1 ** (3. * (1. + self._wp + apiv * self._wa)) * \
            np.exp(-3. * self._wa * z / zp1)

    def __repr__(self):
        retstr = "{0}H0={1:.3g}, Om0={2:.3g}, Ode0={3:.3g}, wp={4:.3g}, "\
                 "wa={5:.3g}, zp={6:.3g}, Tcmb0={7:.4g}, Neff={8:.3g}, "\
                 "m_nu={9})"
        return retstr.format(self._namelead(), self._H0, self._Om0,
                             self._Ode0, self._wp, self._wa, self._zp,
                             self._Tcmb0, self._Neff, self.m_nu)


class w0wzCDM(FLRW):
    """FLRW cosmology with a variable dark energy equation of state
    and curvature.

    The equation for the dark energy equation of state uses the
    simple form: :math:`w(z) = w_0 + w_z z`.

    This form is not recommended for z > 1.

    Parameters
    ----------

    H0 : float or `~astropy.units.Quantity`
        Hubble constant at z = 0. If a float, must be in [km/sec/Mpc]

    Om0 : float
        Omega matter: density of non-relativistic matter in units of the
        critical density at z=0.

    Ode0 : float
        Omega dark energy: density of dark energy in units of the critical
        density at z=0.

    w0 : float
        Dark energy equation of state at z=0. This is pressure/density for dark
        energy in units where c=1. A cosmological constant has w0=-1.0.

    wz : float
        Derivative of the dark energy equation of state with respect to z.

    Tcmb0 : float or `~astropy.units.Quantity`
        Temperature of the CMB z=0. If a float, must be in [K]. Default: 2.725.

    Neff : float
        Effective number of Neutrino species. Default 3.04.

    m_nu : float or ndarray or `~astropy.units.Quantity`
        Mass of each neutrino species, in eV. If this is a float or scalar
        Quantity, then all neutrino species are assumed to have that mass. If a
        ndarray or array Quantity, then these are the values of the mass of
        each species. The actual number of neutrino species (and hence the
        number of elements of m_nu if it is not scalar) must be the floor of
        Neff. Usually this means you must provide three neutrino masses unless
        you are considering something like a sterile neutrino.

    name : str
        Optional name for this cosmological object.

    Examples
    --------
    >>> from astropy.cosmology import w0wzCDM
    >>> cosmo = w0wzCDM(H0=70, Om0=0.3, Ode0=0.7, w0=-0.9, wz=0.2)

    The comoving distance in Mpc at redshift z:

    >>> z = 0.5
    >>> dc = cosmo.comoving_distance(z)
    """

    def __init__(self, H0, Om0, Ode0, w0=-1., wz=0., Tcmb0=2.725,
                 Neff=3.04, m_nu=u.Quantity(0.0, u.eV), name=None):

        FLRW.__init__(self, H0, Om0, Ode0, Tcmb0, Neff, m_nu, name=name)
        self._w0 = float(w0)
        self._wz = float(wz)

    @property
    def w0(self):
        """ Dark energy equation of state at z=0"""
        return self._w0

    @property
    def wz(self):
        """ Derivative of the dark energy equation of state w.r.t. z"""
        return self._wz

    def w(self, z):
        """Returns dark energy equation of state at redshift ``z``.

        Parameters
        ----------
        z : array_like
          Input redshifts.

        Returns
        -------
        w : ndarray, or float if input scalar
          The dark energy equation of state

        Notes
        ------
        The dark energy equation of state is defined as
        :math:`w(z) = P(z)/\\rho(z)`, where :math:`P(z)` is the
        pressure at redshift z and :math:`\\rho(z)` is the density
        at redshift z, both in units where c=1.  Here this is given by
        :math:`w(z) = w_0 + w_z z`.
        """

        if isiterable(z):
            z = np.asarray(z)

        return self._w0 + self._wz * z

    def de_density_scale(self, z):
        """ 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)
        """

        if isiterable(z):
            z = np.asarray(z)
        zp1 = 1. + z
        return zp1 ** (3. * (1. + self._w0 - self._wz)) *\
            np.exp(-3. * self._wz * z)

    def __repr__(self):
        retstr = "{0}H0={1:.3g}, Om0={2:.3g}, "\
                 "Ode0={3:.3g}, w0={4:.3g}, wz={5:.3g} Tcmb0={6:.4g}, "\
                 "Neff={7:.3g}, m_nu={8})"
        return retstr.format(self._namelead(), self._H0, self._Om0,
                             self._Ode0, self._w0, self._wz, self._Tcmb0,
                             self._Neff, self.m_nu)

# Pre-defined cosmologies. This loops over the parameter sets in the
# parameters module and creates a LambdaCDM or FlatLambdaCDM instance
# with the same name as the parameter set in the current module's namespace.
# Note this assumes all the cosmologies in parameters are LambdaCDM,
# which is true at least as of this writing.

for key in parameters.available:
    par = getattr(parameters, key)
    if par['flat']:
        cosmo = FlatLambdaCDM(par['H0'], par['Om0'], Tcmb0=par['Tcmb0'],
                              Neff=par['Neff'],
                              m_nu=u.Quantity(par['m_nu'], u.eV),
                              name=key)
        docstr = "%s instance of FlatLambdaCDM cosmology\n\n(from %s)"
        cosmo.__doc__ = docstr % (key, par['reference'])
    else:
        cosmo = LambdaCDM(par['H0'], par['Om0'], par['Ode0'],
                          Tcmb0=par['Tcmb0'], Neff=par['Neff'],
                          m_nu=u.Quantity(par['m_nu'], u.eV), name=key)
        docstr = "%s instance of LambdaCDM cosmology\n\n(from %s)"
        cosmo.__doc__ = docstr % (key, par['reference'])
    setattr(sys.modules[__name__], key, cosmo)

# don't leave these variables floating around in the namespace
del key, par, cosmo

#########################################################################
# The science state below contains the current cosmology.
#########################################################################


class default_cosmology(ScienceState):
    """
    The default cosmology to use.  To change it::

        >>> from astropy.cosmology import default_cosmology, WMAP7
        >>> with default_cosmology.set(WMAP7):
        ...     # WMAP7 cosmology in effect

    Or, you may use a string::

        >>> with default_cosmology.set('WMAP7'):
        ...     # WMAP7 cosmology in effect
    """
    _value = 'WMAP9'

    @staticmethod
    def get_cosmology_from_string(arg):
        """ Return a cosmology instance from a string.
        """
        if arg == 'no_default':
            cosmo = None
        else:
            try:
                cosmo = getattr(sys.modules[__name__], arg)
            except AttributeError:
                s = "Unknown cosmology '%s'. Valid cosmologies:\n%s" % (
                    arg, parameters.available)
                raise ValueError(s)
        return cosmo

    @classmethod
    def validate(cls, value):
        if value is None:
            value = 'WMAP9'
        if isinstance(value, six.string_types):
            return cls.get_cosmology_from_string(value)
        elif isinstance(value, Cosmology):
            return value
        else:
            raise TypeError("default_cosmology must be a string or Cosmology instance.")


@deprecated('0.4', alternative='astropy.cosmology.default_cosmology.get_cosmology_from_string')
def get_cosmology_from_string(arg):
    """ Return a cosmology instance from a string.
    """
    return default_cosmology.get_cosmology_from_string(arg)


@deprecated('0.4', alternative='astropy.cosmology.default_cosmology.get')
def get_current():
    """ Get the current cosmology.

    If no current has been set, the WMAP9 comology is returned and a
    warning is given.

    Returns
    -------
    cosmo : ``Cosmology`` instance
    """
    return default_cosmology.get()


@deprecated('0.4', alternative='astropy.cosmology.default_cosmology.set')
def set_current(cosmo):
    """ Set the current cosmology.

    Call this with an empty string ('') to get a list of the strings
    that map to available pre-defined cosmologies.

    Parameters
    ----------
    cosmo : str or ``Cosmology`` instance
      The cosmology to use.
    """
    return default_cosmology.set(cosmo)


DEFAULT_COSMOLOGY = ScienceStateAlias(
    '0.4', 'DEFAULT_COSMOLOGY', 'default_cosmology', default_cosmology)