Solovay functions and their applications in algorithmic randomness
Classical versions of Kolmogorov complexity are incomputable. Nevertheless, in 1975 Solovay showed that there are computable functions f≥K+O(1) such that for infinitely many strings σ, f(σ)=K(σ)+O(1), where K denotes prefix-free Kolmogorov complexity. Such an f is now called a Solovay function. We p...
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| Main Authors: | , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
18 May 2015
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| In: |
Journal of computer and system sciences
Year: 2015, Volume: 81, Issue: 8, Pages: 1575-1591 |
| ISSN: | 1090-2724 |
| DOI: | 10.1016/j.jcss.2015.04.004 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1016/j.jcss.2015.04.004 Verlag, lizenzpflichtig, Volltext: http://www.sciencedirect.com/science/article/pii/S0022000015000422 
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| Author Notes: | Laurent Bienvenu, Rod Downey, André Nies, Wolfgang Merkle |
| Summary: | Classical versions of Kolmogorov complexity are incomputable. Nevertheless, in 1975 Solovay showed that there are computable functions f≥K+O(1) such that for infinitely many strings σ, f(σ)=K(σ)+O(1), where K denotes prefix-free Kolmogorov complexity. Such an f is now called a Solovay function. We prove that many classical results about K can be obtained by replacing K by a Solovay function. For example, the three following properties of a function g all hold for the function K.(i)The sum of the terms ∑n2−g(n) is a Martin-Löf random real.(ii)A sequence A is Martin-Löf random if and only if g(A↾n)>n−O(1).(iii)A sequence A is K-trivial if and only if K(A↾n)<g(n)+O(1). We show that when fixing any of these three properties, then among all computable functions exactly the Solovay functions possess this property. Furthermore, this characterization extends accordingly to the larger class of right-c.e. functions. |
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| Item Description: | Gesehen am 25.05.2020 |
| Physical Description: | Online Resource |
| ISSN: | 1090-2724 |
| DOI: | 10.1016/j.jcss.2015.04.004 |