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

[Mike Miller]

Update of bug #44930 (project octave):

                  Status:               Need Info => Invalid                

    _______________________________________________________

Follow-up Comment #5:

Doug is correct, and it does belong in the zplane function because that it
what the function is intended to do. It is used to show the poles and zeros of
a filter when the arguments are row vectors.

I think you are expecting that the vectors of coefficients you pass to the
zplane function are for positive powers of z. If that were the case, you would
be right. But


zplane ([1, 2, 3])


is not working on the polynomial H(z) = z^2 + 2z + 3, it is the polynomial
H(z) = 1 + 2z^-1 + 3z^-2.

If you want to plot only zeros with no poles, you will have to calculate the
zeros yourself with the roots function and pass the column vector of zeros to
zplane. Sorry if you find that wrong, but that is the documented interface of
the zplane function.

    _______________________________________________________

Reply to this item at:

  <http://savannah.gnu.org/bugs/?44930>

_______________________________________________
  Message sent via/by Savannah
  http://savannah.gnu.org/