A typical simulation run is shown in Fig. 4 . Again, the prices tend towards an approximate equilibrium, although it is impossible for them to settle completely due to the nature of the algorithm. A second algorithm that can be used in situations where sellers have no direct knowledge of competitors or buyers is the derivative-following algorithm. A derivative follower starts by measuring its profitability and then perturbing its price up or down by a random amount. A typical simulation run with step size chosen uniformly between 0 and 0.02 is shown in Fig. 5 .
All buyers are quality-sensitive.