Hi, I have a stable continuous system, generated as:
num=[-10 -8.8 4.9 -4.4 6.2];
den=[1 16.41 73.63 78.68 64.51 37.02];
sys=tf(num,den);

pzmap() indicates stability and step funtion is stable.
WHen I discretise using z=c2d(sys,0.2) and run pzmap(z) all of my poles and zeros are on the
rhs of the real axis indicating instability??
However, the step response of z still appears stable and looks like the original sys??
Very confused. Can anyone explain please?

Thanks

Hi, I have a stable continuous system, generated as:
>num=[-10 -8.8 4.9 -4.4 6.2];
>den=[1 16.41 73.63 78.68 64.51 37.02];
>sys=tf(num,den);
>
>pzmap() indicates stability and step funtion is stable.
>WHen I discretise using z=c2d(sys,0.2) and run pzmap(z) all of my poles and zeros are on
the rhs of the real axis indicating instability??
>However, the step response of z still appears stable and looks like the original sys??
>Very confused. Can anyone explain please?
>
>Thanks
>
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Hello,

a discrete-time system is stable only if all of it's poles lie inside the unit circle.

When you discretize a stable continuous-time system with a sampling rate that preserves the
stability then the entire left-half-plane is mapped in the interior of the unit circle.

Manolis