×

Oscillation in the initial segment complexity of random reals. (English) Zbl 1222.03047

Schnorr long ago showed that a real \(A\) is Martin-Löf random iff \(K(A\upharpoonright n)\geq n\) for all \(n\) (up to a constant) where \(A\upharpoonright n \) denotes the first \(n\) bits of \(A\) and \(K\) denotes prefix-free Kolmogorov complexity. Natural questions arise: How far can \(K(A\upharpoonright n)\) be above \(n\), how often is it close to \(n\), is there any gap behaviour or the like. This paper is devoted to questions like these. It follows in the tradition of early work by, particularly, Solovay and earlier Chaitin. The authors extend a result of Chaitin by giving a provably tight upper bound on the number of strings \(\sigma\) of length \(n\) with \(K(\sigma)<n+K(n)-m\). Using this proof, they show that \(\sum 2^{-g(n)}\) diverges iff \(\exists^\infty n\, K(A\upharpoonright n)>n+g(n)\) for all Martin-Löf random \(A\). This improves an earlier result of Solovay who had the result for \(g\) computable. Naturally, the general case is significantly more complex, and uses very different techniques. Miller and Yu use this result to prove that there are comparable \(K\)-degrees of random reals. Namely, there are 1-random \(A\) and \(B\) such that, for all \(n\), \(K(A\upharpoonright n)<^+ K(B\upharpoonright n)\), and these can be \(\Delta^0_2\). Also proven are facts about the size of downward and upward cones in the \(K\)-degrees. The techniques are ingenious and rely on machine simulations. Miller and Yu use a result of Erdős and Révész to give necessary and sufficient conditions on a function \(f\) so that \(K(A\upharpoonright n) \geq n+K(n) +f(n)\) for all \(n\) and for almost all \(A\), namely \(\sum 2^{-f(n)-K(f(n)|n^*)}<\infty\). If \(\sum 2^{-f(n)-K(f(n)|n^*)}=\infty\) then \(K(A\upharpoonright n) < n+K(n) +f(n)\) for all \(n\) and for almost all \(A\). A number of interesting corollaries are derived. Finally, in a completely different direction, it is shown that it is independent of ZFC whether every chain of 1-random \(K\)-degrees of size \(< \aleph_0^2\) has a lower bound in the 1-random \(K\)-degrees.

MSC:

03D32 Algorithmic randomness and dimension
68Q30 Algorithmic information theory (Kolmogorov complexity, etc.)
03E35 Consistency and independence results
Full Text: DOI

References:

[1] Aleksandrov, P. S., Sur la puissance des ensembles mesurables \(B\), C. R. Acad. Sci. Paris, 162, 323-325 (1916) · JFM 46.0301.01
[2] Barmpalias, George; Lewis, Andrew E. M.; Soskova, Mariya, Randomness lowness and degrees, J. Symbolic Logic, 73, 2, 559-577 (2008) · Zbl 1145.03020
[3] Bartoszyński, Tomek, Additivity of measure implies additivity of category, Trans. Amer. Math. Soc., 281, 1, 209-213 (1984) · Zbl 0538.03042
[4] Bartoszyński, T.; Judah, H., Set Theory: On the Structure of the Real Line (1995), AK Peters Ltd.: AK Peters Ltd. Wellesley, MA · Zbl 0834.04001
[5] Chaitin, Gregory J., A theory of program size formally identical to information theory, J. Assoc. Comput. Mach., 22, 329-340 (1975) · Zbl 0309.68045
[6] Chaitin, Gregory J., Incompleteness theorems for random reals, Adv. in Appl. Math., 8, 2, 119-146 (1987) · Zbl 0649.03046
[7] Downey, Rod G.; Hirschfeldt, Denis R.; LaForte, Geoff, Randomness reducibility (extended abstract), (Mathematical Foundations of Computer Science. Mathematical Foundations of Computer Science, Mariánské Lázně, 2001. Mathematical Foundations of Computer Science. Mathematical Foundations of Computer Science, Mariánské Lázně, 2001, Lecture Notes in Comput. Sci., vol. 2136 (2001), Springer: Springer Berlin), 316-327 · Zbl 0999.03038
[8] Downey, Rod G.; Hirschfeldt, Denis R.; LaForte, Geoff, Randomness reducibility, J. Comput. System Sci., 68, 1, 96-114 (2004), see [7] for an extended abstract · Zbl 1072.03024
[9] Downey, R. G.; Hirschfeldt, D. R., Algorithmic Randomness and Complexity (2010), Springer-Verlag New York, Inc.: Springer-Verlag New York, Inc. Secaucus, NJ · Zbl 1221.68005
[10] Erdős, Paul; Révész, Pál, On the length of the longest head-run, (Topics in Information Theory, Second Colloq.. Topics in Information Theory, Second Colloq., Keszthely, 1975. Topics in Information Theory, Second Colloq.. Topics in Information Theory, Second Colloq., Keszthely, 1975, Colloq. Math. Soc. János Bolyai, vol. 16 (1977), North-Holland: North-Holland Amsterdam), 219-228 · Zbl 0362.60044
[11] Gács, Péter, The symmetry of algorithmic information, Dokl. Akad. Nauk SSSR, 218, 1265-1267 (1974)
[12] Gács, Péter, Every sequence is reducible to a random one, Inf. Control, 70, 2-3, 186-192 (1986) · Zbl 0628.03024
[13] Harrington, Leo; Marker, David; Shelah, Saharon, Borel orderings, Trans. Amer. Math. Soc., 310, 1, 293-302 (1988) · Zbl 0707.03042
[14] Jech, Thomas, Set Theory, Springer Monogr. Math. (2003), Springer-Verlag: Springer-Verlag Berlin · Zbl 1007.03002
[15] Jockusch, Carl G.; Soare, Robert I., \( \Pi_1^0\) classes and degrees of theories, Trans. Amer. Math. Soc., 173, 33-56 (1972) · Zbl 0262.02041
[16] Bjørn Kjos-Hanssen, Joseph S. Miller, Reed Solomon, Lowness notions, measure, and domination, in press.; Bjørn Kjos-Hanssen, Joseph S. Miller, Reed Solomon, Lowness notions, measure, and domination, in press. · Zbl 1262.03068
[17] Kučera, Antonín, Measure \(\Pi_1^0\)-classes and complete extensions of PA, (Recursion Theory Week. Recursion Theory Week, Oberwolfach, 1984. Recursion Theory Week. Recursion Theory Week, Oberwolfach, 1984, Lecture Notes in Math., vol. 1141 (1985), Springer: Springer Berlin), 245-259 · Zbl 0622.03031
[18] Kunen, K., Set Theory, An Introduction to Independence Proofs, Stud. Logic Found. Math., vol. 102 (1980), North-Holland Publishing Co.: North-Holland Publishing Co. Amsterdam · Zbl 0443.03021
[19] L.A. Levin, Some theorems on the algorithmic approach to probability theory and information theory, Dissertation in Mathematics, Moscow University, 1971.; L.A. Levin, Some theorems on the algorithmic approach to probability theory and information theory, Dissertation in Mathematics, Moscow University, 1971.
[20] Levin, L. A., Laws of information conservation (non-growth) and aspects of the foundation of probability theory, Probl. Inf. Transm., 10, 3, 206-210 (1974)
[21] Li, M.; Vitányi, P., An Introduction to Kolmogorov Complexity and Its Applications, Texts Comput. Sci. (2008), Springer: Springer New York · Zbl 1185.68369
[22] Martin-Löf, Per, The definition of random sequences, Inf. Control, 9, 602-619 (1966) · Zbl 0244.62008
[23] Martin-Löf, Per, Complexity oscillations in infinite binary sequences, Z. Wahrscheinlichkeitstheor. Verw. Geb., 19, 225-230 (1971) · Zbl 0212.23103
[24] Miller, Joseph S., The \(K\)-degrees, low for \(K\)-degrees, and weakly low for \(K\) sets, Notre Dame J. Form. Log., 50, 4, 381-391 (2010), 2009 · Zbl 1213.03053
[25] Miller, Joseph S.; Liang, Yu, On initial segment complexity and degrees of randomness, Trans. Amer. Math. Soc., 360, 6, 3193-3210 (2008) · Zbl 1140.68028
[26] Nies, André, Lowness properties and randomness, Adv. Math., 197, 1, 274-305 (2005) · Zbl 1141.03017
[27] Nies, A., Computability and Randomness, Oxford Logic Guides, vol. 51 (2009), Oxford University Press: Oxford University Press Oxford · Zbl 1169.03034
[28] Rényi, A., Probability Theory, North-Holland Ser. Appl. Math. Mech., vol. 10 (1970), North-Holland Publishing Co.: North-Holland Publishing Co. Amsterdam, translated by László Vekerdi · Zbl 0206.18002
[29] Shoenfield, Joseph R., The problem of predicativity, (Essays on the Foundations of Mathematics (1961), Magnes Press, Hebrew Univ.: Magnes Press, Hebrew Univ. Jerusalem), 132-139 · Zbl 0173.00903
[30] Robert M. Solovay, Draft of paper (or series of papers) on Chaitin’s work, May 1975, unpublished notes, 215 p.; Robert M. Solovay, Draft of paper (or series of papers) on Chaitin’s work, May 1975, unpublished notes, 215 p.
[31] M. van Lambalgen, Random sequences, PhD Dissertation, University of Amsterdam, 1987.; M. van Lambalgen, Random sequences, PhD Dissertation, University of Amsterdam, 1987.
[32] van Lambalgen, Michiel, The axiomatization of randomness, J. Symbolic Logic, 55, 3, 1143-1167 (1990) · Zbl 0724.03026
[33] Yu, Liang; Decheng, Ding; Downey, Rod G., The Kolmogorov complexity of random reals, Ann. Pure Appl. Logic, 129, 1-3, 163-180 (2004) · Zbl 1065.03025
[34] Zvonkin, A. K.; Levin, L. A., The complexity of finite objects and the development of the concepts of information and randomness by means of the theory of algorithms, Russian Math. Surveys, 25, 6, 83-124 (1970) · Zbl 0222.02027
This reference list is based on information provided by the publisher or from digital mathematics libraries. Its items are heuristically matched to zbMATH identifiers and may contain data conversion errors. In some cases that data have been complemented/enhanced by data from zbMATH Open. This attempts to reflect the references listed in the original paper as accurately as possible without claiming completeness or a perfect matching.