title: What does numpy.gradient do?
body: <p>So I know what the gradient of a (mathematical) function is, so I feel like I should know what <code>numpy.gradient</code> does. But I don't. The <a href="http://docs.scipy.org/doc/numpy/reference/generated/numpy.gradient.html" rel="noreferrer">documentation</a> is not really helpful either:</p>
  
  <blockquote>
    <p>Return the gradient of an N-dimensional array.</p>
  </blockquote>
  
  <p>What is the gradient of an array? When is <code>numpy.gradient</code> useful?</p>