更改

In graph theory an undirected graph has two kinds of incidence matrices: unoriented and oriented.  

In graph theory an undirected graph has two kinds of incidence matrices: unoriented and oriented.  

在图论中，'''<font color="#ff8000">无向图 Undirected Graph</font>'''有两种关联矩阵: 无向图和有向图。

在图论中，'''<font color="#ff8000">无向图 Undirected Graph</font>'''有两种关联矩阵: 无向矩阵和有向关联矩阵。