title: Accessing / modifying submatrix of sparse scipy matrix
body: <p>Suppose I have some Scipy sparse csr matrix, <code>A</code>, and a set of indices, <code>inds=[i_1,...,i_n]</code>. I can access the submatrix given by the rows and columns given in <code>inds</code> via <code>A[inds,:][:,inds]</code>. But I cannot figure out how to modify them. All of the following fail (i.e. do not change the matrix values):</p>
  
  <ul>
  <li><code>A[inds,:][:,inds] *= 5.0</code></li>
  <li><code>(A[inds,:][:,inds]).multiply(5.0)</code></li>
  <li><code>A[inds,:][:,inds] = 5.0</code></li>
  </ul>
  
  <p>Is there any easy way to modify a submatrix of a sparse matrix? </p>