from scipy.interpolate import *
import numpy as np

omegab = 0.049
omegac = 0.261
omegam = omegab + omegac
h      = 0.68
ns     = 0.965
sigma8 = 0.81

c = 3e5

H0 = 100*h
nz = 100000
z1 = 0.0
z2 = 6.0
za = np.linspace(z1,z2,nz)
dz = za[1]-za[0]

H      = lambda z: H0*np.sqrt(omegam*(1+z)**3+1-omegam)
dchidz = lambda z: c/H(z)

chia = np.cumsum(dchidz(za))*dz

zofchi = interp1d(chia,za)
chiofz = interp1d(za,chia)