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理解不上了
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Suppose that the following conditions are met: . Each element of a set consists of k distinguishable parts x1, . . . , xk. . There are n1 possibilities for the first part x1. . For each i = 2, . . . , k and each combination (x1, . . . , xi−1) of the first i − 1parts, there are ni possibilities for the ith part xi . Under these conditions, there are n1 . . . nk elements of the set. The third condition requires only that the number of possibilities for xi be ni no matter what the earlier parts are. For example, for i = 2, it does not require that the same n2 possibilities be available for x2 regardless of what x1 is. It only requires that the number of possibilities for x2 be n2 no matter what x1 is. for example 后面的怎么理解不上来呢？请帮忙啊！ |
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wzh0408: 金币+1, ok 2014-10-16 22:21:29
| It basically means x1,x2,...,xk are independent. That means x1 can equal, eg, 1,2, ..., 10. x2 can also equal 1,2, ..,8. x3 can also equal 2,..,10. Then the set can have duplicated elements, which is not the usual set as we have before. |
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