问题描述：平均路径长度是网络中另一个重要的特征度量，他是网络中所有节点对之间的平均最短距离。这里节点间的距离指的是从一个节点要经历的边的最小数目，其中所有节点之间的最大距离称为网络的直径。平均路径长度和直径衡量的是网络的传输性能与效率。平均路径长度的公式为



，其中dij表示点i和j之间的最短距离（若dij不存在时，dij就不能加入，且分母要相应减1）



要求：输入邻接矩阵表示的图，计算其平均路径长度-Descr iption of the problem: the average path length is another important network characteristics measure between all pairs of nodes in the network, the average shortest distance. Here the distance between nodes refers to the minimum number from one node to be subjected to the edge, wherein the maximum distance is referred to as the diameter of the network between all nodes. The average path length and diameter measurement of the performance and efficiency of the network' s transmission. The formula of the average path length, where dij indicates the shortest distance between points i and j (if dij is not present, dij can not join, and the denominator accordingly minus 1) requirements: Input adjacency matrix shows, to calculate its average path length