title: Iteratively computing scipy matrix multiplication
body: <p>I have a sparse_csr matrix c and d:</p>
  
  <pre><code>a=np.array([[1,0,1],[0,0,1]])
  b=np.array([[1,1,1],[1,0,1],[0,0,0]])
  
  c=sparse.csr_matrix(a)
  d=sparse.csr_matrix(b)
  </code></pre>
  
  <p>I am iteratively multiplying c and d like this:</p>
  
  <pre><code>for j in range(3):
      c_new = d.dot(c.T).T
      c = c_new
  </code></pre>
  
  <p>I observed the <code>type(c)</code> is <code>&lt;class 'scipy.sparse.csc.csc_matrix'&gt;</code>. This slows down to do matrix computation for large matrix inside every iteration. Is there any way to speed up the process keeping the "csr" format.</p>