An output characteristic of a monotonic system is controlled using a plurality of adjustable inputs. The adjustments are controlled using a set of setpoints and a set of dither magnitudes. Each input's adjustment is controlled simultaneously using a setpoint and a dither around the setpoint. The dither values for each input have a zero mean and there is zero correlation between the dithers applied to different inputs. The changes in the output characteristic that result from the dithers are measured, and are used to create an adjustment value. The adjustment value is used to create a set of adjusted dither magnitudes. The set of adjusted dither magnitudes are added to a set of integrated prior adjusted dither magnitudes to create a set of setpoint adjustments. Adding the setpoint adjustments to corresponding setpoints creates a set of updated setpoints. This process is repeated so that the setpoints converge on a value that maximizes the output characteristic being controlled.