title: Matrix multiplication for sparse matrices in Python
body: <p>I want to multiply a sparse matrix A, with a matrix B which has 0, -1, or 1 as elements. To reduce the complexity of the matrix multiplication, I can ignore items if they are 0, or go ahead and add the column without multiplication if the item is 1, or subs. if it's -1. The discussion about this is here:</p>
  
  <p><a href="https://stackoverflow.com/questions/7474508/random-projection-algorithm-pseudo-code">Random projection algorithm pseudo code</a></p>
  
  <p>Now I can go ahead and implement this trick but I wonder if I use Numpy's multiplication functions it'll be faster.</p>
  
  <p>Does anyone knows if they optimised matrix multiplication for such matrices? Or can you suggest something to speed this process up since I have a matrix 300000x1000.</p>