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Chebyshev Type II analog lowpass filter prototype
[z,p,k] = cheb2ap(n,Rs)
[z,p,k] = cheb2ap(n,Rs) finds the zeros, poles, and gain of an order n Chebyshev Type II analog lowpass filter prototype with stopband ripple Rs dB down from the passband peak value. cheb2ap returns the zeros and poles in length n column vectors z and p and the gain in scalar k. If n is odd, z is length n-1. The transfer function is
Chebyshev Type II filters are monotonic in the passband and equiripple in the stopband. The pole locations are the inverse of the pole locations of cheb1ap, whose poles are evenly spaced about an ellipse in the left half plane. The Chebyshev Type II stopband edge angular frequency ω_{0} is set to 1 for a normalized result. This is the frequency at which the stopband begins and the filter has magnitude response of 10^{–Rs/20}.