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On Indistinguishability Operators, Fuzzy Metrics and Modular Metrics

Department of Mathematics and Computer Science, Universitat de les Illes Balears, Carretera de Valldemossa km. 7.5, 07122 Palma, Spain
Author to whom correspondence should be addressed.
Axioms 2017, 6(4), 34;
Received: 20 November 2017 / Revised: 8 December 2017 / Accepted: 12 December 2017 / Published: 15 December 2017
(This article belongs to the Special Issue New Trends in Fuzzy Set Theory and Related Items)
PDF [303 KB, uploaded 18 December 2017]


The notion of indistinguishability operator was introduced by Trillas, E. in 1982, with the aim of fuzzifying the crisp notion of equivalence relation. Such operators allow for measuring the similarity between objects when there is a limitation on the accuracy of the performed measurement or a certain degree of similarity can be only determined between the objects being compared. Since Trillas introduced such kind of operators, many authors have studied their properties and applications. In particular, an intensive research line is focused on the metric behavior of indistinguishability operators. Specifically, the existence of a duality between metrics and indistinguishability operators has been explored. In this direction, a technique to generate metrics from indistinguishability operators, and vice versa, has been developed by several authors in the literature. Nowadays, such a measurement of similarity is provided by the so-called fuzzy metrics when the degree of similarity between objects is measured relative to a parameter. The main purpose of this paper is to extend the notion of indistinguishability operator in such a way that the measurements of similarity are relative to a parameter and, thus, classical indistinguishability operators and fuzzy metrics can be retrieved as a particular case. Moreover, we discuss the relationship between the new operators and metrics. Concretely, we prove the existence of a duality between them and the so-called modular metrics, which provide a dissimilarity measurement between objects relative to a parameter. The new duality relationship allows us, on the one hand, to introduce a technique for generating the new indistinguishability operators from modular metrics and vice versa and, on the other hand, to derive, as a consequence, a technique for generating fuzzy metrics from modular metrics and vice versa. Furthermore, we yield examples that illustrate the new results. View Full-Text
Keywords: indistinguishability operator; fuzzy (pseudo-)metric; modular (pseudo-)metric; continuous Archimedean t-norm; additive generator; pseudo-inverse indistinguishability operator; fuzzy (pseudo-)metric; modular (pseudo-)metric; continuous Archimedean t-norm; additive generator; pseudo-inverse
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Miñana, J.-J.; Valero, O. On Indistinguishability Operators, Fuzzy Metrics and Modular Metrics. Axioms 2017, 6, 34.

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