一种“不对称"的结构.成对距离矩阵 [英] An "asymmetric" pairwise distance matrix

问题描述

假设要比较三个序列:a，b和c.传统上，所得的3×3成对距离矩阵是对称，表示从a到b的距离等于从b到a的距离.

Suppose there are three sequences to be compared: a, b, and c. Traditionally, the resulting 3-by-3 pairwise distance matrix is symmetric, indicating that the distance from a to b is equal to the distance from b to a.

我想知道TraMineR是否提供某种方式来生成非对称成对距离矩阵.

I am wondering if TraMineR provides some way to produce an asymmetric pairwise distance matrix.

推荐答案

不，正是由于Pat的评论中强调的原因，TraMineR不会产生共性"差异.

No, TraMineR does not produce 'assymetric' dissimilaries precisely for the reasons stressed in Pat's comment.

计算序列之间的成对差异的主要兴趣是，一旦我们有了这样的差异，我们就可以

The main interest of computing pairwise dissimilarities between sequences is that once we have such dissimilarities we can for instance

• 测量序列之间的差异，确定邻域，查找类固醇，...
• 运行集群算法，自组织地图，MDS，...
• 对序列进行类方差分析
• 为序列增加回归树

在这些过程中输入非对称异种矩阵很可能会产生不相关的结果.

Inputting a non symmetric dissimilarity matrix in those processes would most probably generate irrelevant outcomes.

由于这种对称性要求，用于计算最佳匹配距离的替代成本必须对称.重要的是不要将替代成本解释为从一种状态切换到另一种状态的成本，而是要了解它们的含义，即编辑成本.例如，比较两个序列时 aabcc和aadcc，我们可以通过在第一个中将b任意替换为d或在第二个中将d替换为b来使它们相等.那么，对于两个替代品不给出相同的成本是没有道理的.

It is because of this symmetry requirement that the substitution costs used for computing Optimal Matching distances MUST be symmetrical. It is important to not interpret substitution costs as the cost of switching from one state to the other, but to understand them for what they are, i.e., edit costs. When comparing two sequences, for example aabcc and aadcc, we can make them equal either by replacing arbitrarily b with d in the first one or d with b in the second one. It would then not make sense not giving the same cost for the two substitutions.

希望这会有所帮助.

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