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arXiv 1702.04779cs.CC
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压缩复杂度

Compression Complexity

Stephen Fenner, Lance Fortnow

摘要:

x的柯尔莫哥洛夫复杂度,记为C(x),是生成x的最短程序的长度。对于这样一个简单的定义,Kolmogorov复杂性有着丰富而深刻的理论,以及在学习理论、复杂性下界和SAT算法等各种主题中的应用。Kolmogorov复杂度通常集中在解压缩,从压缩的程序到原始字符串。本文提出了压缩的双重概念,即从字符串到其压缩版本的映射。典型的无损压缩算法(如Lempel-Ziv或Huffman编码)总是产生一个将恢复到原始的字符串。我们定义了一个一般的压缩概念的基础上,这一观察。对于每个m,我们展示了长度约为m的单个压缩算法q,对于n和长度n >= m的字符串x,q的输出将具有C(x)的n-m+O(1)位内的长度。我们还证明了这个界是强紧的,对于每个n >= m,有一个长度为n的x,C(x)约为m,使得大小略小于m的压缩程序根本不能压缩x。我们还考虑了一个多项式时间有界版本的压缩复杂性,并表明,类似的结果,这个版本将排除密码单向函数。

英文摘要:

The Kolmogorov complexity of x, denoted C(x), is the length of the shortest program that generates x. For such a simple definition, Kolmogorov complexity has a rich and deep theory, as well as applications to a wide variety of topics including learning theory, complexity lower bounds and SAT algorithms. Kolmogorov complexity typically focuses on decompression, going from the compressed program to the original string. This paper develops a dual notion of compression, the mapping from a string to its compressed version. Typical lossless compression algorithms such as Lempel-Ziv or Huffman Encoding always produce a string that will decompress to the original. We define a general compression concept based on this observation. For every m, we exhibit a single compression algorithm q of length about m which for n and strings x of length n >= m, the output of q will have length within n-m+O(1) bits of C(x). We also show this bound is tight in a strong way, for every n >= m there is an x of length n with C(x) about m such that no compression program of size slightly less than m can compress x at all. We also consider a polynomial time-bounded version of compression complexity and show that similar results for this version would rule out cryptographic one-way functions.

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