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Universal finitary codes with exponential tails

Nate Harvey·Alexander E. Holroyd·Yuval Peres·Dan Romik
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Abstract

In 1977, Keane and Smorodinsky showed that there exists a finitary homomorphism from any finite-alphabet Bernoulli process to any other finite-alphabet Bernoulli process of strictly lower entropy. In 1996, Serafin proved the existence of a finitary homomorphism with finite expected coding length. In this paper, we construct such a homomorphism in which the coding length has exponential tails. Our construction is source-universal, in the sense that it does not use any information on the source distribution other than the alphabet size and a bound on the entropy gap between the source and target distributions. We also indicate how our methods can be extended to prove a source-specific version of the result for Markov chains.

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Nate Harvey, Alexander E. Holroyd, Yuval Peres, Dan Romik. 2005-02-23. Universal finitary codes with exponential tails. https://arxiv.org/abs/math/0502484

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