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I found that scatter matrices are useful to calculate within and between class separability. This link gives more information about them. My question is as follows:

Suppose there are 4-classes, I should get 4 within-class scatter matrices and 4C2 = 6 between-class scatter matrices. Whereas, we get only single within and between class matrices. Any explanation for this?

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Even in the link you've provided (which is kind of brief) you can see the per-class scatter matrices S_i. But "between-class" doesn't mean "between all pairs of classes", it means something closer to "among all classes" -- so there's a single "between-class" matrix.

于 2013-06-19T11:37:36.753 回答