title: dot products on sparse matrices
body: <p>I'm trying to take the dot product of a row in a sparse matrix with the transpose of that row using Python. I have a huge sparse matrix called X2. And I am saving the results (which is supposed to be a single number) in a list called Njc. </p>
  
  <pre><code>    X2 = X.transpose()
      for row in X2:
          Njc.append(dot(row,row.transpose()))
  </code></pre>
  
  <p>However, when I run my program, the results are not single numbers. They look like:
    (0, 0)    355</p>
  
  <p>(0, 0)    295</p>
  
  <p>(0, 0)    15</p>
  
  <p>(0, 0)    204</p>
  
  <p>(0, 0)    66</p>
  
  <p>....</p>
  
  <p>Unfortunately my sparse matrix is so huge that I can't make it into a dense matrix (my memory will blow up). Is there a way to get only the numbers on the right without the couples on the left?</p>