A control unit and a control method are disclosed. First and second changing units change impedances of two or more first and second components within predetermined first and second ranges, respectively, the first and the second components affecting an output signal. An evaluation function value calculating unit calculates an evaluation function value that is dependent on the impedances of the first and the second components. A gradient vector calculating unit calculates a gradient vector based on the difference between the evaluation function values before and after the impedance change of the second components. Based on the gradient vector, impedance of each of the first components is changed such that the evaluation function value takes a desired value.