This paper deals with the eigenvalue problem of the multiple eigenvalue filter which was proposed in the previous paper, "Parallel Learning in Control Systems (Derivation of Multiple Eigen value Filter)". The system with proposed filter derived by means of parallel learning not only reduces control variable deviation without decreasing stability, but also has PID (Proportional, Integral and Derivative) control action although the original control system before learning has just proportional control action. In this paper, the reason is shown from the view point of eigenvalue problem and Nyquist stability theory.
