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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"I'm having problems with the `ax` parameters of the `rlocus` function","articleBody":"I was trying today to plot the root locus of a transfer function, but wanted to pass a specific axes object to it, so I tried to use the `ax` parameter of the `rlocus` function:\r\n\r\n```\r\nfrom control import *\r\nimport matplotlib.pyplot as plt\r\n\r\ns = tf([1, 0], 1)\r\nG = 1/(s*(s+1))\r\n\r\nfig, ax = plt.subplots(dpi=200)\r\nrlocus(G, ax=ax)\r\n```\r\n\r\nBut when doing this, the following error was raised:\r\n\r\n```\r\n---------------------------------------------------------------------------\r\nUnboundLocalError                         Traceback (most recent call last)\r\n\u003cipython-input-1-80498c4b1a54\u003e in \u003cmodule\u003e\r\n      6 \r\n      7 fig, ax = plt.subplots(dpi=200)\r\n----\u003e 8 rlocus(G, ax=ax)\r\n\r\n~\\anaconda3\\lib\\site-packages\\control\\rlocus.py in root_locus(sys, kvect, xlim, ylim, plotstr, plot, print_gain, grid, ax, **kwargs)\r\n    173 \r\n    174         if print_gain and not sisotool:\r\n--\u003e 175             fig.canvas.mpl_connect(\r\n    176                 'button_release_event',\r\n    177                 partial(_RLClickDispatcher, sys=sys, fig=fig,\r\n\r\nUnboundLocalError: local variable 'fig' referenced before assignment\r\n```\r\n\r\nControl version: 0.9.0 ","author":{"url":"https://github.com/jolenscki","@type":"Person","name":"jolenscki"},"datePublished":"2021-05-22T00:32:24.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/623/python-control/issues/623"}