Correlation matrix between our observables for the 20 redshift bins in an Euclid-like survey, at ℓ = 10. This matrix corresponds to the D_{g,  z,  κCMB}(ℓ = 10) data vector. The value in each pixel corresponds to . All the data vectors considered in Eqs. (19)–(20) are a subset of this matrix. We see that there is no correlation between δ_g and δ_z inside the same redshift bin (diagonals of the upper-left and lower-right blocks), and that there are opposite and positive correlations for neighbouring bins.