Parameters a and b defined in Eq. (12) and measured by least squares applied to each value of R_s used to obtain λ_CV in the MG-COLA set of simulations. The error bars (small in the right panel) are given by the square root of the diagonal elements in the covariance matrix. Both parameters have been approximated to an exponential type function plotted in red, whose constants are given in Table 4. The result of the approximation is a fit ${\lambda }_{\mathrm{CV}}^{\mathrm{fit}}(R_{\mathrm{s}},z)$ represented in Fig. 5 by dashed lines.