I'm just getting my head around the zplane function. I'm not how the values of z and p are mapped onto the pole-zero plot. I thought zeros and poles were supposed to have both real and imaginary parts - as these are the axes of the pole-zero plot. But in the examples of zplane code given in the help documentation the z and p values are just single real values. Also, for a 4 pole/zero filter there are 5 values for z and also for p. Shouldn't this be four?
zplane is a little subtle. When B and A are rows, they represent transfer functions. However, if B and A are columns, they are zeros and poles.
[b,a] = ellip(4,.5,20,.6); zplane(b,a) zplane(roots(b),roots(a))