René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Any plan for step_info to support negative step responses?","articleBody":"I have step responses that go negative and sometimes stay negative, and it breaks the settling time calculation and rise time calculation. I've been messing around with it and might open a pull request if this is something y'all would be interested in. \r\n\r\nFor example, here is my code, the step response plot, and the error\r\n\r\n```python\r\nfrom control import tf, step_response, step_info\r\nimport matplotlib.pyplot as plt\r\nimport numpy as np\r\n\r\ntransfer_function = tf( [3.32, 0, -162.8], [1, 24.56, 186.5, 457.8, 116.2] )\r\ntime, response = step_response(transfer_function)\r\n\r\nfig, ax = plt.subplots(1, 1)\r\nax.plot(time, response)\r\nplt.show()\r\n\r\nstep_info(transfer_function)\r\n```\r\n\r\n![step_response](https://user-images.githubusercontent.com/8628581/63395443-5ecdeb00-c389-11e9-963a-24804b81aada.png)\r\n\r\n`step_info()` gives the following error\r\n\r\n```\r\nTraceback (most recent call last):\r\n  File \"bug_test.py\", line 14, in \u003cmodule\u003e\r\n    step_info(transfer_function)\r\n  File \"/Users/hgducharme/Programming/pendulum/env/lib/python3.7/site-packages/control/timeresp.py\", line 536, in step_info\r\n    SettlingTime = T[i + 1]\r\nIndexError: index 1000 is out of bounds for axis 0 with size 1000\r\n```\r\n\r\nWhen I run this code in MATLAB, I get the following result\r\n\r\n\u003cbr\u003e\r\n\r\n\u003cimg width=\"644\" alt=\"Screen Shot 2019-08-20 at 8 36 44 PM\" src=\"https://user-images.githubusercontent.com/8628581/63395721-427e7e00-c38a-11e9-8ca3-25cd7bb7ce7d.png\"\u003e","author":{"url":"https://github.com/hgducharme","@type":"Person","name":"hgducharme"},"datePublished":"2019-08-21T01:37:25.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/337/python-control/issues/337"}