ComplexWarning while trying to plot a pzmap #288
Description
I would like to understand why the zeros from my sys3 transfer function below aren't being plotted by the pzmap function.
#sys1
num = [6., 0., 1.]
den = [1., 3., 3., 1.]
sys = control.tf(num, den)
#sys2
n1 = [1., 1.]
n2 = [1., 2.]
d1 = [1., 2.j]
d2 = [1., -2.j]
d3 = [1., 3.]
num2 = np.convolve(n1, n2)
den2 = np.convolve(d1,np.convolve(d2, d3))
sys2 = control.tf(num2, den2)
#sys3
num3 = np.convolve(num, den2)
den3 = np.convolve(den, num2)
sys3 = control.tf(num3, den3)
control.pzmap(sys3, Plot=True, title="Mapa de polos e zeros")
When control.pzmap runs, it returns the correct poles and zeros, together with a plot. The problem is, this plot contains only the roots of the sys3 transfer function. Together with the plot, I am also getting the following warning message:
xxx/anaconda3/lib/python3.7/site-packages/control/xferfcn.py:864: ComplexWarning: Casting complex values to real discards the imaginary part
num[i, j, np+1-len(numpoly):np+1] = numpoly[::-1]
If the problem is the removal of the imaginary parts by that part of the algorithm, why is that happening then?