Return a depthfirst ordering starting with specified node.
Note that a depthfirst order is not unique. Furthermore, for graphs with cycles, the tree generated by a depthfirst search is not unique either.
New in version 0.11.0.
Parameters :  csgraph : array_like or sparse matrix
i_start : int
directed : bool, optional
return_predecessors : bool, optional


Returns :  node_array : ndarray, one dimension
predecessors : ndarray, one dimension
