说明：  从整个符号序列出发，根据各信源序列的概率将信源序列映射到[0,1) 区间上，然后选取区间内的一点（也就是一个二进制的小数）来表示信源序列。
(From the entire sequence of symbols, the source sequence is mapped to the interval [0,1] according to the probability of each source sequence, and then a point (that is, a binary fraction) in the interval is selected to represent the source sequence.)