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From: moonman on 3 Jul 2010 14:04
num=[0 1 0]
den=[1 -5/2 1]
x=[1 zeros(1,10)]
y=filter(num,den,x)

If i make change in x, raise value to higher than 10, my answer changes
why
From: Wayne King on 3 Jul 2010 16:39
"moonman " <moonnightingale(a)yahoo.com> wrote in message <i0nu2k$sob$1(a)fred.mathworks.com>...
> num=[0 1 0]
> den=[1 -5/2 1]
> x=[1 zeros(1,10)]
> y=filter(num,den,x)
>
> If i make change in x, raise value to higher than 10, my answer changes
> why

Hi, This is not a stable filter. You can see that with:

zplane(num,den)

You have a pole outside the unit circle. The impulse response is not absolutely summable and you can see that by increasing N and watching the impulse response grow without bound. Try a few increasing N for


[h,~] = impz(num,den,N);
stem(h);

Hope that helps,
Wayne
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