Frequency response from a transfer function?

FREQS Laplace-transform (s-domain) frequency response. H = FREQS(B,A,W) returns the complex frequency response vector H of the filter B/A: nb-1 nb-2 B(s) b(1)s + b(2)s + ... + b(nb) H(s) = ---- = ------------------------------------- na-1 na-2 A(s) a(1)s + a(2)s + ... + a(na) given the numerator and denominator coefficients in vectors B and A. The frequency response is evaluated at the points specified in vector W (in rad/s). The magnitude and phase can be graphed by calling FREQS(B,A,W) with no output arguments. [H,W] = FREQS(B,A) automatically picks a set of 200 frequencies W on which the frequency response is computed. FREQS(B,A,N) picks N frequencies. % Example 1: % Find and graph the frequency response of the transfer function % given by % H(s) = ( 0.2*s^2 + 0.3*s + 1 )/( s^2 + 0.4s + 1 ) a = [1 0.4 1]; % Numerator coefficients b = [0.2 0.3 1]; % Denominator coefficients w = logspace(-1,1); % Frequency vector freqs(b,a,w) % Example 2: % Design a fifth-order analog lowpass Bessel filter with an % approximate constant group delay up to 10,000 rad/s and plot % the frequency response of the filter using freqs. [b,a] = besself(5,10000); % Bessel analog filter design freqs(b,a) % Plot frequency response See also LOGSPACE, POLYVAL, INVFREQS, and FREQZ. Documentation for freqs doc freqs