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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Unexpected behavior for a system defined using zpk","articleBody":"I been scratching my head about whats going on with a very simple system.\r\nDefining the system using tf yields results as expected. But defining the system through zpk does not.\r\n\r\n## Description\r\nI intend to define the next system:\r\n```\r\nG(s) =           K\r\n          ---------------\r\n           (s+2)*(s+2/3)\r\n```\r\nWith K adjusted for a ts=1 second. Very straight forward.\r\n\r\n## Reproduction\r\nThis is my code for zpk:\r\n\r\n```\r\nimport control as ct\r\nimport numpy as np\r\nimport matplotlib.pyplot as plt\r\nK = 10.314\r\nG = ct.zpk([], [-2, -2/3], K)\r\nT = ct.feedback(G)\r\nct.step_response(T).plot()\r\n```\r\n![image](https://github.com/user-attachments/assets/a4d310bf-6e7b-457e-9d78-bad56917cd0c)\r\n\r\n`ct.step_info(T)`\r\n```\r\n{'RiseTime': np.float64(0.0),\r\n 'SettlingTime': nan,\r\n 'SettlingMin': np.float64(-4.959514534383556e+52),\r\n 'SettlingMax': np.float64(8.010508330340013e+51),\r\n 'Overshoot': np.float64(9.04605979182796e+53),\r\n 'Undershoot': np.float64(5.600651440127666e+54),\r\n 'Peak': np.float64(4.959514534383556e+52),\r\n 'PeakTime': np.float64(5.180816459236604),\r\n 'SteadyStateValue': np.float64(0.8855245835956728)}\r\n```\r\n\r\nThe result is not as expected. While defining the system through tf:\r\n\r\n```\r\nI = ct.tf([K], [1, 8/3, 4/3])\r\nV = ct.feedback(I)\r\nct.step_response(V).plot()\r\n```\r\n![image](https://github.com/user-attachments/assets/7ad3809e-2ca3-4743-a99a-064a9063c7f7)\r\n\r\n`ct.step_info(V)`\r\n```\r\n{'RiseTime': np.float64(0.4186518350898263),\r\n 'SettlingTime': np.float64(2.5119110105389577),\r\n 'SettlingMin': np.float64(0.8127467853231765),\r\n 'SettlingMax': np.float64(1.118911703975943),\r\n 'Overshoot': np.float64(26.35435717033743),\r\n 'Undershoot': 0,\r\n 'Peak': np.float64(1.118911703975943),\r\n 'PeakTime': np.float64(0.9942981083383374),\r\n 'SteadyStateValue': np.float64(0.8855347207912633)}\r\n\r\n```\r\nOutputting both system definitions reveals they're the same. The transfer function is exactly the same. But I don't know what may be going on with the transfer object defined with zpk.\r\n\r\n## System info\r\nI've installed the control package in a clean conda enviroment and using a jupyter notebook through VSCode.\r\n\r\nConda:\r\n```\r\nconda version : 23.1.0\r\nconda-build version : 3.22.0\r\npython version : 3.9.13.final.0\r\nvirtual packages : __archspec=1=x86_64__win=0=0\r\nplatform : win-64\r\n```\r\n\r\n\r\n","author":{"url":"https://github.com/gereze","@type":"Person","name":"gereze"},"datePublished":"2024-11-27T12:15:55.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/1067/python-control/issues/1067"}