when they see the light, they turn using the stop **behavior (that consists in fast** rotation), and then go to the light using the obstacle avoidance**. However, once** on the recharge area, they use the stop **until the energy level is back over 90%.**
Investigating deeper, it appears that the speeds of the light following and area sweeper **are lower than that of the** obstacle avoidance **– and speed is crucial**
in this experiment. Further experiments will have to modify the speeds of all behaviors to see if it makes any difference. However, this also demonstrates that the supervisor can discard some behavior that proves under-optimal or useless.

## 6.4 Sensitivity Analysis

One critical issue of the proposed approach is how to ensure that the "right" behavior will be available to the supervisor. A possible solution is to propose a large choice - but will the supervisor be able to retain only the useful **ones? In** order to assess this, the same energy experiment was repeated but many useless, or even harmful, behaviors were added to the 4 basic behaviors.

First, 4 behaviors were added to the existing ones: random, light avoiding, crash **(goes straight into the nearest wall!) and** stick to the walls **(tries to stay**
close to a wall). The first generations demonstrated lower performances and higher variance than in the initial experiment, as all behaviors were used with equal probability. However, the plot of the best fitness (not shown) soon catches up with the plots of Figure 1, and after 150 generations, the results are hardly distinguishable. Looking at the frequency of use of each behavior, **it clearly** appears that the same useful behaviors are used (see Figure 2-left, and section 6.3 for a discussion). Moreover, the useless behaviors are scarcely used as evolution goes along, as can be seen on Figure 2-right (beware of the different scale).

These good stability results have been confirmed by adding 20 useless behaviors (5 times the same useless 4). The results are very similar - though a little worse, of course, as the useless behaviors are called altogether a **little more often.**

![0_image_0.png](0_image_0.png)

