Figure 1.

(Color online) (a) Typical aspect of the logarithm of the cost function F(W,D,α₀) for a fixed value of α₀. The logarithm is shown here in order to enhance the visual contrast. This cost function has one minimum denoted (W^*,D^*) that depends on α₀. (b) Typical aspect of the function log(F(W^*,D^*,α₀)) for varying values of α₀ (W^* and D^* being calculated for each α₀). This cost function has a single minimum.