1. An apparatus for automatically searching for the optimal operating point of a dynamic system, comprising: (a) a dynamic system having one variable input, one variable output responsive to variations of said input, and a relationship between said input and said output that includes an optimal operating point at which said system transitions from a direct-acting to a reverse-acting mode or vice versa; (b) a minimum or maximum setter providing a source of setpoint signals; and (c) an optimizer connected to said setpoint signal source, said output, and said input, said optimizer being arranged to so vary said input as to cause said output to reach said optimal operating point and stay near thereto.