docs: def add_vector(self, vector):
          """\
          Writes the provided vector to the matrix.
  
          `vector`
              An iterable of ``(word-id, word-frequency)`` tuples
          """
          self._num_docs+=1
          max_id, veclen = self._mmw.write_vector(self._num_docs, vector)
          self._num_terms = max(self._num_terms, 1 + max_id)
          self._num_nnz += veclen