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https://en.wikipedia.org/wiki/Distance_matrix
For example, suppose these data are to be analyzed, where pixel Euclidean distance is the distance metric.
https://zh.wikipedia.org/wiki/邻接矩阵
邻接矩阵是表示一个图的常用存储表示。它用两个数组分别存储数据元素（顶点）的信息和数据元素之间的关系（边或弧）的信息。
距离矩阵可算是邻接矩阵的扩充。
https://en.wikipedia.org/wiki/Adjacency_matrix
The distance matrix has in position (i, j) the distance between vertices vi and vj. The distance is the length of a shortest path connecting the vertices. Unless lengths of edges are explicitly provided, the length of a path is the number of edges in it. The distance matrix resembles a high power of the adjacency matrix, but instead of telling only whether or not two vertices are connected (i.e., the connection matrix, which contains boolean values), it gives the exact distance between them.