title: numpy division with RuntimeWarning: invalid value encountered in double_scalars
body: <p>I wrote the following script:</p>
  
  <pre><code>import numpy
  
  d = numpy.array([[1089, 1093]])
  e = numpy.array([[1000, 4443]])
  answer = numpy.exp(-3 * d)
  answer1 = numpy.exp(-3 * e)
  res = answer.sum()/answer1.sum()
  print res
  </code></pre>
  
  <p>But I got this result and with the error occurred:</p>
  
  <pre><code>nan
  C:\Users\Desktop\test.py:16: RuntimeWarning: invalid value encountered in double_scalars
    res = answer.sum()/answer1.sum()
  </code></pre>
  
  <p>It seems to be that the input element were too small that python turned them to be zeros, but indeed the division has its result.</p>
  
  <p>How to solve this kind of problem?</p>