Correlation matrix computed with the training set. A moderate correlation (0.3−0.6) is found between the shape of the continuum in the Lyman-α forest (1020  ≤  λ  ≤  1210 Å) and in the region between Lyman-α and C iv emission lines (1216  ≤  λ  ≤  1600 Å), in agreement with S05. We also note a moderate anti-correlation (from −0.6 to −0.4) between the continuum in the Lyman-α forest and the region further to the C iv emission line.