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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Strange nondeterministic issues when using `phase_plot` with `X`, `Y` and `X0` set","articleBody":"I am trying to draw a phase plot with both streamlines and a vector field. Using the inverted pendulum ODE from https://python-control.readthedocs.io/en/latest/phaseplots.html, I put together the following script:\r\n```python\r\nimport numpy as np\r\nimport matplotlib.pyplot as plt\r\nfrom control.phaseplot import phase_plot\r\n\r\n# Define the ODEs for a damped (inverted) pendulum\r\ndef invpend_ode(x, t, m=1., l=1., b=0.2, g=1):\r\n    return x[1], -b/m*x[1] + (g*l/m)*np.sin(x[0])\r\n\r\n# Set up the figure the way we want it to look\r\nplt.figure()\r\nplt.title('Inverted pendulum')\r\n\r\n# Outer trajectories\r\nphase_plot(\r\n    invpend_ode,\r\n    X=(-10, 10, 20),\r\n    Y=(-10, 10, 20),\r\n    X0=[[-2*np.pi, 1.6], [-2*np.pi, 0.5], [-1.8, 2.1],\r\n        [-1, 2.1], [4.2, 2.1], [5, 2.1],\r\n        [2*np.pi, -1.6], [2*np.pi, -0.5], [1.8, -2.1],\r\n        [1, -2.1], [-4.2, -2.1], [-5, -2.1]]\r\n)\r\n\r\nplt.show()\r\n```\r\n\r\nI would have expected this to plot a simple vector field with a grid of 20*20 arrows and streamlines from the given inital conditions. Instead, each time I run this I get a different malformed plot, often with at least one axis somehow having arrows at values like 10^281. Various RuntimeWarnings about overflow are also sometimes printed in the console. Some examples of the plots I have gotten:\r\n\r\n![image](https://github.com/python-control/python-control/assets/5256211/cd64a25d-a389-4ee7-b90f-a9ff62d0d78d)\r\n![image](https://github.com/python-control/python-control/assets/5256211/753939bd-bc6a-4066-a2d4-3b6763f86d33)\r\n![image](https://github.com/python-control/python-control/assets/5256211/d6f05d7f-644c-4422-ad6d-c524be9fb18d)\r\n![image](https://github.com/python-control/python-control/assets/5256211/688dcb8a-ec0f-4a00-98ef-38f28ba0a3df)\r\n![image](https://github.com/python-control/python-control/assets/5256211/6f498b69-9ea1-4e07-b3dd-89e75793c34d)\r\n\r\nThis does not seem like expected behaviour. What is going on here?\r\n\r\nTested on Windows 10 with Python 3.10.11, matplotlib 3.8.2 and control 0.9.4 from pip.","author":{"url":"https://github.com/FeldrinH","@type":"Person","name":"FeldrinH"},"datePublished":"2024-02-13T23:57:59.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/970/python-control/issues/970"}