log (λ) versus log (φ). Factor f varies from f = 0.99 (left), f = 0.75 (center) to f = 0.5 (right). Each of these curves starts with three initial values of λ₀, dotted line (λ₀ = 10), dashed line (λ₀ = 1) and solid line (λ₀ = 0.1). See text for details. The vertical gray solid line shows the selected value of ϵ = 10^-7 as a criterion to finish the iteration process. The horizontal gray solid line shows the value of λ = 0.2956 (log (λ) = −0.53) obtained using the L–Curve or GCV methods.