-fix error for stochastic
-rprop graphs:
 * iterations as a function of nMax
 * generalization error as a function of nMax
 pick the best nMax, lRate, momentum
 * iterations / nb neurons : backprop batch, backprop stoch, rprop
 * gen error / nb neurons : backprop batch, backprop stoch, rprop
 * iterations / nb layers : _
 * gen error / nb layers : _
