Wed 06 Dec 2017 05:41:43 PM UTC, comment #1:
Also, invfreqz(h,w,3,3,wt,30) shown below doesn't return the same result as matlab (see https://edoras.sdsu.edu/doc/matlab/toolbox/signal/spectop9.html)
>> [b,a] = butter(4,0.4)
b =
0.046583 0.186332 0.279497 0.186332 0.046583
a =
1.000000 -0.782095 0.679979 -0.182676 0.030119
>> [h,w] = freqz(b,a,64);
>> [b4,a4] = invfreqz(h,w,4,4)
b4 =
0.046583 0.186332 0.279497 0.186332 0.046583
a4 =
1.000000 -0.782095 0.679979 -0.182676 0.030119
>> wt = ones(size(w));
>> [b30,a30] = invfreqz(h,w,3,3,wt,30)
b30 =
0.046389 0.178546 0.244578 0.127586
a30 =
1.00000 -0.95016 0.73823 -0.20056
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