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On shape-preserving additions of fuzzy intervals. (English) Zbl 0993.03070
For given left and right shapes $$L$$ and $$R$$, the corresponding $$LR$$-fuzzy intervals are characterized by 4 parameters describing their kernel and their support. Triangular norm-based addition of fuzzy quantities is, in general, a process with high computational complexity. However, in the case of processing $$LR$$-fuzzy numbers (intervals) by means of some specific t-norm preserving the shapes $$L$$ and $$R$$, the processing is reduced to processing the parameters only, thus efficiently reducing the computational complexity.
Specific cases of shape-preservation were given by A. Kolesárová [Tatra Mt. Math. Publ. 6, 75-81 (1995; Zbl 0851.04005)] (for linear shapes) and by R. Mesiar [Fuzzy Sets Syst. 86, 73-78 (1997; Zbl 0921.04002)], requiring the convexity of composite functions $$fL$$ and $$fR$$, where $$f$$ is an additive generator of the t-norm $$T$$ [see E. P. Klement, R. Mesiar and E. Pap, Triangular norms, Dordrecht: Kluwer (2000; Zbl 0972.03002)].
The present paper completely solves the characterization of all shape preserving additions of fuzzy numbers based on continuous t-norms, confirming the hypothesis of Mesiar from 1997. Note that the characterizations of non-continuous t-norms leading to the shape-preserving additions of $$LR$$-fuzzy numbers (intervals) is still an open problems.

##### MSC:
 3e+72 Theory of fuzzy sets, etc.
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