Signal Toolkit - invfreqz

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

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

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

Fit filter B(z)/A(z)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: normalized frequency (0 to pi) (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,A] = butter(4,1/4);
     [H,F] = freqz(B,A);
     [Bh,Ah] = invfreq(H,F,4,4);
     Hh = freqz(Bh,Ah);
     disp(sprintf('||frequency response error|| = %f',norm(H-Hh)));