% error: zplane(b [, a]) or zplane(z [, p]) % % Plot the poles and zeros. If the arguments are row vectors then they % represent filter coefficients (numerator polynomial b and denominator % polynomial a), but if they are column vectors or matrices then they % represent poles and zeros. % % This is a horrid interface, but I didn't choose it; better would be % to accept b,a or z,p,g like other functions. The saving grace is % that poly(x) always returns a row vector and roots(x) always returns % a column vector, so it is usually right. You must only be careful % when you are creating filters by hand. % % Note that due to the nature of the roots function, poles and zeros % may be displayed as occurring around a circle rather than at a single % point. % % The transfer function is % % B(z) b0 + b1 z^(-1) + b2 z^(-2) + ... + bM z^(-M) % H(z) = ---- = -------------------------------------------- % A(z) a0 + a1 z^(-1) + a2 z^(-2) + ... + aN z^(-N) % % b0 (z - z1) (z - z2) ... (z - zM) % = -- z^(-M+N) ------------------------------ % a0 (z - p1) (z - p2) ... (z - pN) % % The denominator a defaults to 1, and the poles p defaults to [].