Correct models of fuzzy IF--THEN rules are continuous

  • Authors:
  • Irina Perfilieva;Stephan Lehmke

  • Affiliations:
  • University of Ostrava, Institute for Research and Applications of Fuzzy Modeling, 30. dubna 22, 701 03 Ostrava 1, Czech Republic;University of Dortmund, D-44221 Dortmund, Germany

  • Venue:
  • Fuzzy Sets and Systems
  • Year:
  • 2006

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Abstract

We show that a system of fuzzy IF-THEN rules being modeled correctly works as a partially given (fuzzy) function. Its behavior is determined by a chosen structure for IF-THEN rules which assigns meaning to fuzzy sets in the IF and THEN parts as well as to basic connectives. This partial function can be extended to a whole domain of fuzzy sets with the help of the Compositional Rule of Inference which plays a role of a mechanism for computing the dependent functional values. We investigate the question whether this function is continuous. Two new notions are introduced: a correct model of fuzzy IF-THEN rules in a structure and a continuous model of fuzzy IF-THEN rules with respect to given data. We prove that correctness of models of fuzzy IF-THEN rules is connected with the problem of solvability of the respective system of fuzzy relation equations. In this and only this case a model of fuzzy IF-THEN rules is continuous. As a side result we have established a new criterion of a solvability of a system of fuzzy relation equations with sup-*-composition.