invfreqs

Compute analog filter coefficients from frequency response values.

Syntax

[b,a] = invfreqs(h,f,nb,na)

[b,a] = invfreqs(h,f,nb,na,w)

Inputs

h
The complex frequency response values.
Type: double
Dimension: vector
f
The frequencies corresponding to h (in radians/sec).
Type: double
Dimension: vector
nb
The filter numerator polynomial order.
Type: integer
Dimension: scalar
na
The filter denominator polynomial order.
Type: integer
Dimension: scalar
w
Optional weights applied to acheive a weighted fitting of the response values.
Type: double
Dimension: vector

Outputs

b
The estimated numerator polynomial coefficients of the filter.
Type: double
Dimension: vector
a
The estimated denominator polynomial coefficients of the filter.
Type: double
Dimension: vector

Example

Recover coefficients from the output of an analog Chebyshev I filter.

order = 3;
wc = (2*pi)*100;
[b1,a1] = cheby1(order, 1, wc, 's')
w = [0:0.2:2] * wc;
h = freqs(b1,a1,w);
[b2,a2] = invfreqs(h,w,order,order)
b1 = [Matrix] 1 x 4
0.00000e+00  0.00000e+00  0.00000e+00  1.21869e+08
a1 = [Matrix] 1 x 4
1.00000e+00  6.20993e+02  4.88904e+05  1.21869e+08
b2 = [Matrix] 1 x 4
6.57632e-17  2.15327e-14  6.91457e-11  1.21869e+08
a2 = [Matrix] 1 x 4
1.00000e+00  6.20993e+02  4.88904e+05  1.21869e+08