René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"contour for cyclic functions","articleBody":"I tried to get a contour plot of the complex angles of a particular function, but always got one level too many around zeros and infinities. Consider the following MWE which is supposed to plot the contour line for `pi / 4` only. It plots `pi / 4` alright, but also `pi`.\r\n```python\r\nimport numpy as np\r\nimport matplotlib.pyplot as plt\r\n\r\nxmin, xmax = -3.0, 3.0\r\nymin, ymax = -3.0, 3.0\r\nnx, ny = 500, 500\r\n\r\nx = np.linspace(xmin, xmax, nx)\r\ny = np.linspace(ymin, ymax, ny)\r\nX, Y = np.meshgrid(x, y)\r\nfZ = np.angle(X + 1j * Y)\r\n\r\nplt.contour(X, Y, fZ, levels=[0.25 * np.pi], colors=\"k\")\r\nplt.gca().set_aspect(\"equal\")\r\nplt.show()\r\n```\r\n![screenshot](https://user-images.githubusercontent.com/181628/123930099-b5e27500-d98f-11eb-8339-0864d5f80e7d.png)\r\n\r\nThis is with mpl 3.4.2.\r\n\r\n_Edit:_ A very similar report is [on stackoverflow](https://stackoverflow.com/q/16197171/353337).","author":{"url":"https://github.com/nschloe","@type":"Person","name":"nschloe"},"datePublished":"2021-06-30T08:49:30.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/20548/matplotlib/issues/20548"}