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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"ComplexWarning while trying to plot a pzmap","articleBody":"I would like to understand why the zeros from my sys3 transfer function below aren't being plotted by the `pzmap` function.\r\n\r\n```\r\n#sys1\r\nnum = [6., 0., 1.]\r\nden = [1., 3., 3., 1.]\r\nsys = control.tf(num, den)\r\n\r\n#sys2\r\nn1 = [1., 1.]\r\nn2 = [1., 2.]\r\nd1 = [1., 2.j]\r\nd2 = [1., -2.j]\r\nd3 = [1., 3.]\r\nnum2 = np.convolve(n1, n2)\r\nden2 = np.convolve(d1,np.convolve(d2, d3))\r\nsys2 = control.tf(num2, den2)\r\n\r\n#sys3\r\nnum3 = np.convolve(num, den2)\r\nden3 = np.convolve(den, num2)\r\nsys3 = control.tf(num3, den3)\r\n\r\ncontrol.pzmap(sys3, Plot=True, title=\"Mapa de polos e zeros\")\r\n```\r\n\r\nWhen `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:\r\n\r\n```\r\nxxx/anaconda3/lib/python3.7/site-packages/control/xferfcn.py:864: ComplexWarning: Casting complex values to real discards the imaginary part\r\n  num[i, j, np+1-len(numpoly):np+1] = numpoly[::-1]\r\n```\r\n\r\nIf the problem is the removal of the imaginary parts by that part of the algorithm, why is that happening then?","author":{"url":"https://github.com/fabiomolinar","@type":"Person","name":"fabiomolinar"},"datePublished":"2019-04-10T10:35:48.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/288/python-control/issues/288"}