[Octave-bug-tracker] [bug #44930] signal package: zplane shows non-existent poles and zeros

[Doug Stewart]

Follow-up Comment #3, bug #44930 (project octave):

No it is not incorrect.


If we start with Laplace space and draw a root Locus we see that the poles
move to zeros. And if there are not enough zeroes then the extra poles move
out radially to Infinity. ( I am giving you the short version of my lectures)
so we can say that there are zeroes out at infinity that these poles are
moving to.

Now when we move all this to the Z plane then we can show that infinity in
Laplace space maps to zero in Z Space. So now all the missing zeroes in
laplace space show up in Z space.  

Of course we can make Z space filters that are not realizable in Laplace
space.
So what is correct or incorrect is relative to what the objective is.

The padding is actually making the zeroes from infinity, show up at the
origin.


Just my 2C worth.

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