title: RuntimeWarning: invalid value encountered in long_scalars
body: <p>I'm having an issue with modifying an array, by adding the percentage of each item compared to its row to a new matrix. This is the code providing error:</p>
  
  <pre><code>for j in range(1,27):
          for k in range(1,27):
                  let_prob[j,k] = let_mat[j,k]*100/(let_mat[j].sum())
  </code></pre>
  
  <p>I get the error:</p>
  
  <blockquote>
    <p>RuntimeWarning: invalid value encountered in long_scalars</p>
  </blockquote>
  
  <p>I have tried rounding the denominator to no success.</p>