title: "Divide by zero encountered in log" when not dividing by zero
body: <p>When I do:</p>
  
  <pre><code>summing += yval * np.log(sigmoid(np.dot(w.transpose(), xi.transpose()))) + (1-yval)* np.log(1-sigmoid(np.dot(w.transpose(), xi.transpose())))
  </code></pre>
  
  <p>where there is no division, why do I get a "divide by zero encountered in log" error? As a result, <code>summing</code> becomes <code>[nan]</code>.</p>