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我想弄清楚如何证明Lempel ZIV 77压缩算法真的给了最佳压缩。LZ 77压缩算法
我发现下面的信息:
So how well does the Lempel-Ziv algorithm work? In these notes, we’ll
calculate two quantities. First, how well it works in the worst case, and
second, how well it works in the random case where each letter of the message
is chosen uniformly and independently from a probability distribution, where
the ith letter appears with probability pi
. In both cases, the compression
is asymptotically optimal. That is, in the worst case, the length of the
encoded string of bits is n + o(n). Since there is no way to compress all
length-n strings to fewer than n bits, this can be counted as asymptotically
optimal. In the second case, the source is compressed to length
α
H(p1, p2, . . . , pα)n + o(n) = n∑(-pi log2 pi) + O(n)
i=1
which is to first order the Shannon bound.
这到底是怎么意思? 为什么没有办法将所有长度为n的字符串压缩为少于n位?
谢谢大家。
首先,感谢您的回答,那么显示Lempel Ziv压缩的最佳方法是什么?最佳的方法是渐进式的,至少是渐进式的 。 – user11001
我不是这方面的专家,所以我只能做一个快速的网络搜索。我可以看到关于这个主题的证据,但是它们比我想要通过娱乐工作更长,更详细,并且即使这样,三个中的两个都将细节留给读者作为练习。所以我不知道通过详细证明的正确方法。 http://www.ifp.illinois.edu/~zzhao/ece563/handouts/LZ71.pdf是没有练习的文章,但它是一篇期刊文章,所以它可能不会更容易遵循。 – mcdowella