code: def compute_accumulated_cost_matrix(self):
          
          self._setup_dtw()
          if self.dtw is None:
              self.log(u"Inner self.dtw is None => returning None")
              return None
          self.log(u"Returning accumulated cost matrix")
          return self.dtw.compute_accumulated_cost_matrix()
docs: Compute the accumulated cost matrix, and return it.
  
          Return ``None`` if the accumulated cost matrix cannot be computed
          because one of the two waves is empty after masking (if requested).
  
          :rtype: :class:`numpy.ndarray` (2D)
          :raises: RuntimeError: if both the C extension and
                                 the pure Python code did not succeed.
  
          .. versionadded:: 1.2.0