René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"problematic step() output: unstable instead of sinusoidal","articleBody":"I am trying to plot step response of a 3rd order process Gp, controlled with a P controller.\r\nGp = 6/[(s+1)(s+2)(s+3)]\r\nI am using v0.8.3\r\n\r\n```python\r\nfrom control.matlab import *\r\n\r\nGp = tf(6,[1,6,11,6])\r\nGc = 10\r\nGor = Gp*Gc/(1 + Gp*Gc)\r\ny,t = step(Gor)\r\n# Plotting code\r\n```\r\n\r\nGor has 3 poles at (-6, sqrt(11) j, - sqrt(11) j ) and the expected behavior is sinusoidal oscillations after the initial transients have died down (ie t \u003e ~ 2/3)\r\nBut what I get is an unstable system: \r\n![image](https://user-images.githubusercontent.com/5154616/77427036-a45d0580-6dfb-11ea-8760-c928c88c7aa5.png)\r\n\r\nOctave gives the correct result (ymin 0.113, ymax 1.705 after transients):\r\n![image](https://user-images.githubusercontent.com/5154616/77427922-42050480-6dfd-11ea-8e13-3382b0f567d6.png)\r\n","author":{"url":"https://github.com/prashant2","@type":"Person","name":"prashant2"},"datePublished":"2020-03-24T13:00:57.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/384/python-control/issues/384"}