title: Python replace zeros in matrix with 'circle' of ones
body: <p>I can create a large matrix of zeros and replace a rectangular region within the matrix with ones like so:</p>
  
  <pre><code>import numpy as np
  
  z = np.zeros((400,400))
  z[192:206,196:202] = 1
  </code></pre>
  
  <p>How would I replace a <strong>circular</strong> region in the matrix with ones? The circle's radius can be arbitrarily big.</p>