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Entropy and Optimal Compression of Some General Plane Trees

Entropy and Optimal Compression of Some General Plane Trees We continue developing the information theory of structured data. In this article, we study models generating d-ary trees (d 2) and trees with unrestricted degree. We first compute the entropy which gives us the fundamental lower bound on compression of such trees. Then we present efficient compression algorithms based on arithmetic encoding that achieve the entropy within a constant number of bits. A naïve implementation of these algorithms has a prohibitive time complexity of O(nd) elementary arithmetic operations (each corresponding to a number f(n, d) of bit operations), but our efficient algorithms run in O(n2) of these operations, where n is the number of nodes. It turns out that extending source coding (i.e., compression) from sequences to advanced data structures such as degree-unconstrained trees is mathematically quite challenging and leads to recurrences that find ample applications in the information theory of general structures (e.g., to analyze the information content of degree-unconstrained non-plane trees). http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png ACM Transactions on Algorithms (TALG) Association for Computing Machinery

Entropy and Optimal Compression of Some General Plane Trees

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Publisher
Association for Computing Machinery
Copyright
Copyright © 2018 ACM
ISSN
1549-6325
eISSN
1549-6333
DOI
10.1145/3275444
Publisher site
See Article on Publisher Site

Abstract

We continue developing the information theory of structured data. In this article, we study models generating d-ary trees (d 2) and trees with unrestricted degree. We first compute the entropy which gives us the fundamental lower bound on compression of such trees. Then we present efficient compression algorithms based on arithmetic encoding that achieve the entropy within a constant number of bits. A naïve implementation of these algorithms has a prohibitive time complexity of O(nd) elementary arithmetic operations (each corresponding to a number f(n, d) of bit operations), but our efficient algorithms run in O(n2) of these operations, where n is the number of nodes. It turns out that extending source coding (i.e., compression) from sequences to advanced data structures such as degree-unconstrained trees is mathematically quite challenging and leads to recurrences that find ample applications in the information theory of general structures (e.g., to analyze the information content of degree-unconstrained non-plane trees).

Journal

ACM Transactions on Algorithms (TALG)Association for Computing Machinery

Published: Oct 1, 2018

Keywords: Arithmetic coding

References