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On Defining Expressions for Entropy and Cross-Entropy: The Entropic Transreals and Their Fracterm Calculus

Jan A. Bergstra Orcid Logo, John Tucker Orcid Logo

Entropy, Volume: 27, Issue: 1, Start page: 31

Swansea University Author: John Tucker Orcid Logo

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DOI (Published version): 10.3390/e27010031

Abstract

Classic formulae for entropy and cross-entropy contain operations 0 and log2 that are not defined on all inputs. This can lead to calculations with problematic subexpressions such as 0 log2 0 and uncertainties in large scale calculations; partiality also introduces complications in logical analysis....

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Published in: Entropy
ISSN: 1099-4300
Published: MDPI AG 2025
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URI: https://cronfa.swan.ac.uk/Record/cronfa68639
Abstract: Classic formulae for entropy and cross-entropy contain operations 0 and log2 that are not defined on all inputs. This can lead to calculations with problematic subexpressions such as 0 log2 0 and uncertainties in large scale calculations; partiality also introduces complications in logical analysis. Instead of adding conventions or splitting formulae into cases, we create a new algebra of real numbers with two symbols ±∞ for signed infinite values and a symbol named ⊥ for the undefined. In this resulting arithmetic, entropy, cross-entropy, Kullback–Leibler divergence, and Shannon divergence can be expressed without concerning any further conventions. The algebra may form a basis for probability theory more generally.
Keywords: Partial formulae; fracterm calculus; transreals; entropic transreals; peripheral numbers; entropy; cross-entropy
College: Faculty of Science and Engineering
Funders: This research received no external funding.
Issue: 1
Start Page: 31