René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Discontinuous Nyquist Plot","articleBody":"Today I used the following code to produce the nyquist plot of an arbitrary transfer function:\r\n\r\n```\r\nimport numpy as np\r\nfrom control.matlab import *\r\nimport matplotlib.pyplot as plt\r\n\r\na0 = 1.; a1 = 10.; a2 = 31.; a3 = 30\r\nb0 = 1.\r\nnum = np.array([b0])\r\nden = np.array([a3, a2, a1, a0])\r\nsystem_tf = tf(num,den)\r\nctrl_tf = tf([5, 1],[5, 0])\r\nG0 = ctrl_tf*system_tf\r\nGw = feedback(G0,1)\r\nnyquist(Gw)\r\nplt.show()\r\n\r\n```\r\nand I got this strange discontinuous Nyquist plot:\r\n![nyquist](https://user-images.githubusercontent.com/41485443/149620920-49e14ec8-187e-4305-996f-2d26848ff032.png)\r\n\r\nthe bode plot looks correct and I found that both plots use different functions to evaluate the frequency response. So I think there might be a bug in the implementation of the nyquist plot.\r\n\r\nHere is the expected Nyquist plot that I could obtain from Matlab.\r\n![Nyquist_mat](https://user-images.githubusercontent.com/41485443/149621050-bba7f5ad-7551-4a6c-b1e5-6ef4320fcb30.png)\r\n\r\n","author":{"url":"https://github.com/JayEy","@type":"Person","name":"JayEy"},"datePublished":"2022-01-15T12:08:20.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/691/python-control/issues/691"}