Signal Toolkit - invfreqs

Function File: [B,A] = invfreqs(H,F,nB,nA)

: [B,A] = invfreqs(H,F,nB,nA,W)

: [B,A] = invfreqs(H,F,nB,nA,W,iter,tol,'trace')

Fit filter B(s)/A(s)to the complex frequency response H at frequency points F.

A and B are real polynomial coefficients of order nA and nB.

Optionally, the fit-errors can be weighted vs frequency according to the weights W.

Note: all the guts are in invfreq.m

H: desired complex frequency response

F: frequency (must be same length as H)

nA: order of the denominator polynomial A

nB: order of the numerator polynomial B

W: vector of weights (must be same length as F)

Example:

       B = [1/2 1];
       A = [1 1];
       w = linspace(0,4,128);
       H = freqs(B,A,w);
       [Bh,Ah] = invfreqs(H,w,1,1);
       Hh = freqs(Bh,Ah,w);
       plot(w,[abs(H);abs(Hh)])
       legend('Original','Measured');
       err = norm(H-Hh);
       disp(sprintf('L2 norm of frequency response error = %f',err));