（五） Graphivz 箭头连接方向

Ports based on the 8 compass points "n", "ne","e", "se", "s", "sw", "w" or "nw" can be specified for any node.

有八种连接方向：n，ne，e，se，s，sw，w，nw。

digraph G {a->b:n[label="n"];c->d:e[label="e"];e->f:ne[label="ne"];g->h:s[label="s"];i->j:se[label="se"];k->l:w[label="w"];m->n:sw[label="sw"];p->q:nw[label="nw"];A -> B[dir = both,label=both];B -> C[dir = none,label=none];C -> D[dir = back,label=back];D -> A[dir = forward,label=forward];}