code: def setup_interpolant(self):
          
          # for computing nearby (z < 1) redshifts
          zs = numpy.linspace(0., 1., num=self.numpoints)
          ds = self.cosmology.luminosity_distance(zs).value
          self.nearby_d2z = interpolate.interp1d(ds, zs, kind='linear',
                                                  bounds_error=False)
          # for computing far away (z > 1) redshifts
          zs = numpy.logspace(0, numpy.log10(self.default_maxz),
                              num=self.numpoints)
          ds = self.cosmology.luminosity_distance(zs).value
          self.faraway_d2z = interpolate.interp1d(ds, zs, kind='linear',
                                                   bounds_error=False)
          # store the default maximum distance
          self.default_maxdist = ds.max()
docs: Initializes the z(d) interpolation.