title: Algorithmic complexity converting CSR/CSC to BSR
body: <p>I was wondering what is the algorithmic complexity of a conversion from <code>CSC (compressed sparse column)</code> or <code>CSR (compressed sparse row)</code> to <code>BSR (blocked sparse row)</code>?</p>
  
  <p>Say I have </p>
  
  <ul>
  <li>a CSC <code>m x m</code>-matrix <code>A = csc(m,m)</code> with <code>n</code> non-zero elements</li>
  <li>a CSR <code>m x m</code>-matrix <code>B = csr(m,m)</code> with <code>n</code> non-zero elements</li>
  </ul>
  
  <p>BSR format: </p>
  
  <ul>
  <li><p><a href="https://docs.scipy.org/doc/scipy/reference/generated/scipy.sparse.bsr_matrix.html" rel="nofollow noreferrer">https://docs.scipy.org/doc/scipy/reference/generated/scipy.sparse.bsr_matrix.html</a></p></li>
  <li><p><a href="https://software.intel.com/en-us/mkl-developer-reference-c-sparse-blas-bsr-matrix-storage-format" rel="nofollow noreferrer">https://software.intel.com/en-us/mkl-developer-reference-c-sparse-blas-bsr-matrix-storage-format</a></p></li>
  </ul>