On Mon, Jun 15, 2015 at 2:18 AM, Thomas D. Dean <address@hidden> wrote:
Back to my previous problem. I expected to bet the same system from either the zpk or equation representation. But, they are different
octave:1869> clear all
octave:1870> a0 = 1e5;
octave:1871> w1 = 1e4;
octave:1872> w2 = 1e6;
octave:1873> s = tf('s');
octave:1874> a_eqn = a0/(1+s/w1)/(1+s/w2)
Transfer function 'a_eqn' from input 'u1' to output ...
1e+05
y1: --------------------------
1e-10 s^2 + 0.000101 s + 1
Continuous-time model.
octave:1875> a_zpk = zpk([],[w1,w2],a0)
Transfer function 'a_zpk' from input 'u1' to output ...
1e+05
y1: ------------------------
s^2 - 1.01e+06 s + 1e+10
Continuous-time model.
octave:1876> a_eqn(w1)
ans = 4.9495e+04 - 5.0495e+04i
octave:1877> a_zpk(w1)
ans = 4.9495e-06 + 5.0495e-06i
Is this correct? What am I doing wrong?
Tom Dean
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a0/(s+w1)/(s+w2)
a0
_______________
((s+w1)*(s+w2))
a0 1/(w1*w2)
_______________ * ________________
((s+w1)*(s+w2)) 1/(w1*w2)
a0/(w1*w2)
___________________
(s/(w1)+1)* (s/w2)+1)
notice the 1/(w1*w2) in the numerator.