René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Plotting an error band along a curve","articleBody":"### Bug report\r\n\r\n**Bug summary**\r\n\r\npyplot.fill_between(x, y1, y2) does not fill areas, where curves y1 and y2 are crossing.\r\n\r\n**Code for reproduction**\r\n\r\n```python\r\nimport matplotlib.pyplot as plt\r\nimport numpy as np\r\n\r\ndef lissajous(t):\r\n    \"\"\"Calculate Lissajous Curve\"\"\"\r\n    x = np.cos(t)\r\n    y = np.sin(2 * t)\r\n    return x, y\r\n\r\ndata = np.arange(0, 2 * np.pi, 0.01)\r\n\r\nplt.plot(*lissajous(data))\r\nplt.fill_between(\r\n    lissajous(data)[0], lissajous(data)[1] - 0.5, lissajous(data)[1] + 0.5, alpha=0.25\r\n)\r\n\r\nplt.show()\r\n```\r\n\r\n**Actual outcome**\r\n\r\n![Lissajous_issue](https://user-images.githubusercontent.com/47927690/81837956-ca726c80-9545-11ea-9e3d-582b2c4d984c.png)\r\n\r\n**Expected outcome**\r\n\r\n![Lissajous_expected](https://user-images.githubusercontent.com/47927690/81839131-6c468900-9547-11ea-92a0-4cd0c370c399.png)\r\n\r\n**Note**\r\nI came across this problem while trying to use fill_between() as 'errorbars' for parametric functions. If this is not the intended use, I would be glad if someone has suggestions for a workaround.\r\nKeep up the good work!\r\n\r\n**Matplotlib version**\r\n\u003c!--Please specify your platform and versions of the relevant libraries you are using:--\u003e\r\n  * Operating system: Arch Linux x86_64, Kernel 5.6.11-arch1-1\r\n  * Matplotlib version: 3.1.3\r\n  * Matplotlib backend (`print(matplotlib.get_backend())`): Qt5Agg\r\n  * Python version: 3.7.7\r\n  * Jupyter version (if applicable):\r\n  * Other libraries: numpy: 1.18.1\r\n\r\nmatplotlib installed via anaconda\r\n\u003c!--Please tell us how you installed matplotlib and python e.g., from source, pip, conda--\u003e\r\n\u003c!--If you installed from conda, please specify which channel you used if not the default--\u003e\r\n\r\n","author":{"url":"https://github.com/Waljakov","@type":"Person","name":"Waljakov"},"datePublished":"2020-05-13T16:46:14.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/17398/matplotlib/issues/17398"}