title: How to find the minimum value in a numpy matrix?
body: <p>Hey this is a quick and easy question...
  How would i find the minimum value of this matrix, excluding 0?
  As in, 8</p>
  
  <pre><code>arr = numpy.array([[  0.,  56.,  20.,  44.],
                     [ 68.,   0.,  56.,   8.],
                     [ 32.,  56.,   0.,  44.],
                     [ 68.,  20.,  56.,   0.]])
  </code></pre>