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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"polar rgb imshow xticks issue","articleBody":"I'm currently trying to plot an HSV legend, i.e. a circle of color that becomes white as the radius goes to 0. I also posted this question on [stackoverflow](http://stackoverflow.com/questions/21935888/fixing-polar-rgb-imshow-xticks) in the hope of getting a clever workaround.\n\nCode:\n\n```\ndef complex_to_rgb(complex_data, invert=False):\n  from numpy import angle, max, pi, sin, zeros\n  phase = angle(complex_data)\n  amplitude = abs(complex_data)\n  amplitude = amplitude/max(max(amplitude))\n  A = zeros((complex_data.shape[0], complex_data.shape[1], 3))\n  A[:,:,0] = .5*(sin(phase)+1)*amplitude\n  A[:,:,1] = .5*(sin(phase+pi/2)+1)*amplitude\n  A[:,:,2] = .5*(-sin(phase)+1)*amplitude\n  if(invert):\n    return 1-A\n  else:\n    return A\n\nimport numpy as np\nfrom matplotlib.pyplot import figure\n\nN = 1024\nx = np.linspace(-1, 1, N)\ny = np.linspace(-1, 1, N)\n\nX,Y = np.meshgrid(x,y)\n\nR = np.sqrt(X*X + Y*Y)\nPHI = np.arctan2(Y, X)\n\nfig = figure()\nax = fig.add_subplot(111, polar=True)\n\nax.imshow(complex_to_rgb(R*np.exp(1j*PHI)  * (R\u003c1), invert=True))\n\nax.set_xticks([-.5, 0, np.pi/2, np.pi, 3*np.pi/2])#-.5)\nax.set_yticks([0, N/3, 2*N/3, N])\n\nax.set_xticklabels(['', '$0$', r'$\\pi/2$', r'$\\pi$', r'$3\\pi/2$'])\nax.set_yticklabels([])\n\nfig.show()\n```\n\nProblem is, if I change the -.5 xtick (e.g. to +.5), the plot gets messed up and I get division by zero warnings:\n\n```\n....\\lib\\site-packages\\matplotlib\\image.py:161: RuntimeWarning: divide by zero encountered in double_scalars\n  sy = dyintv/viewlim.height\n....\\lib\\site-packages\\matplotlib\\image.py:190: RuntimeWarning: divide by zero encountered in double_scalars\n  sy = dyintv/viewlim.height\n```\n\nI don't want the -.5 arbitrary tick mark. Why does a tick mark influence the drawing of an image?\n","author":{"url":"https://github.com/rubenvb","@type":"Person","name":"rubenvb"},"datePublished":"2014-02-21T13:30:34.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":9},"url":"https://github.com/2827/matplotlib/issues/2827"}