Erratum for Figure 4: in the left column (functions f6 and f10), the figure shows results for the ten target values [1e-8, 1e-7, 1e-6, 1e-5, 1e-4, 1e-2, 1e-1, 1, 10, 100] rather than for 50 target values in ]100,1e-8] as for the remaining figures. The mistake has no decisive impact on the displayed results.