Mutual dimension and random sequences.

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Bibliographic Details
Title: Mutual dimension and random sequences.
Authors: Case, Adam1 adam.case@drake.edu, Lutz, Jack H.2 lutz@iastate.edu
Source: Theoretical Computer Science. Jun2018, Vol. 731, p68-87. 20p.
Subjects: Dimension theory (Topology), Algorithms, Mathematical sequences, Probability theory, Kolmogorov complexity
Abstract: If S and T are infinite sequences over a finite alphabet, then the lower and upper mutual dimensions m d i m ( S : T ) and M d i m ( S : T ) are the upper and lower densities of the algorithmic information that is shared by S and T . In this paper we investigate the relationships between mutual dimension and coupled randomness , which is the algorithmic randomness of two sequences R 1 and R 2 with respect to probability measures that may be dependent on one another. For a restricted but interesting class of coupled probability measures we prove an explicit formula for the mutual dimensions m d i m ( R 1 : R 2 ) and M d i m ( R 1 : R 2 ) , and we show that the condition M d i m ( R 1 : R 2 ) = 0 is necessary but not sufficient for R 1 and R 2 to be independently random. We also identify conditions under which Billingsley generalizations of the mutual dimensions m d i m ( S : T ) and M d i m ( S : T ) can be meaningfully defined; we show that under these conditions these generalized mutual dimensions have the “correct” relationships with the Billingsley generalizations of d i m ( S ) , D i m ( S ) , d i m ( T ) , and D i m ( T ) that were developed and applied by Lutz and Mayordomo; and we prove a divergence formula for the values of these generalized mutual dimensions. [ABSTRACT FROM AUTHOR]
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Abstract:If S and T are infinite sequences over a finite alphabet, then the lower and upper mutual dimensions m d i m ( S : T ) and M d i m ( S : T ) are the upper and lower densities of the algorithmic information that is shared by S and T . In this paper we investigate the relationships between mutual dimension and coupled randomness , which is the algorithmic randomness of two sequences R 1 and R 2 with respect to probability measures that may be dependent on one another. For a restricted but interesting class of coupled probability measures we prove an explicit formula for the mutual dimensions m d i m ( R 1 : R 2 ) and M d i m ( R 1 : R 2 ) , and we show that the condition M d i m ( R 1 : R 2 ) = 0 is necessary but not sufficient for R 1 and R 2 to be independently random. We also identify conditions under which Billingsley generalizations of the mutual dimensions m d i m ( S : T ) and M d i m ( S : T ) can be meaningfully defined; we show that under these conditions these generalized mutual dimensions have the “correct” relationships with the Billingsley generalizations of d i m ( S ) , D i m ( S ) , d i m ( T ) , and D i m ( T ) that were developed and applied by Lutz and Mayordomo; and we prove a divergence formula for the values of these generalized mutual dimensions. [ABSTRACT FROM AUTHOR]
ISSN:03043975
DOI:10.1016/j.tcs.2018.04.003