## Name

yulewalk — least-square filter design

## Calling Sequence

Hz = yulewalk(N,frq,mag)

## Parameters

- N
integer (order of desired filter)

- frq
real row vector (non-decreasing order), frequencies.

- mag
non negative real row vector (same size as frq), desired magnitudes.

- Hz
filter `B(z)/A(z)`

## Description

Hz = yulewalk(N,frq,mag) finds the N-th order iir filter

n-1 n-2
B(z) b(1)z + b(2)z + .... + b(n)
H(z)= ---- = ---------------------------------
n-1 n-2
A(z) z + a(2)z + .... + a(n)

which matches the magnitude frequency response given by vectors frq and mag.
Vectors frq and mag specify the frequency and magnitude of the desired
frequency response. The frequencies in frq must be between 0.0 and 1.0,
with 1.0 corresponding to half the sample rate. They must be in
increasing order and start with 0.0 and end with 1.0.

## Examples

f=[0,0.4,0.4,0.6,0.6,1];H=[0,0,1,1,0,0];Hz=yulewalk(8,f,H);
fs=1000;fhz = f*fs/2;
clf(0);xset('window',0);plot2d(fhz',H');
xtitle('Desired Frequency Response (Magnitude)')
[frq,repf]=repfreq(Hz,0:0.001:0.5);
clf(1);xset('window',1);plot2d(fs*frq',abs(repf'));
xtitle('Obtained Frequency Response (Magnitude)')