'Set ``self._num_scc`` and ``self._scc_proj``
by calling ``scipy.sparse.csgraph.connected_components``:
* docs.scipy.org/doc/scipy/reference/sparse.csgraph.html
* github.com/scipy/scipy/blob/master/scipy/sparse/csgraph/_traversal.pyx
``self._scc_proj`` is a list of length `n` that assigns to each node
the label of the strongly connected component to which it belongs.'

def _find_scc(self):

    (self._num_scc, self._scc_proj) = csgraph.connected_components(self.csgraph, connection='strong')
