Aggregation operators preserving quasiconvexity
Quasiconvexity of a fuzzy set is the necessary and sufficient condition for its cuts to be convex. We study the class of those two variable aggregation operators that preserve quasiconvexity on a bounded lattice, i.e. A(?,?) is quasiconvex for quasiconvex lattice valued fuzzy sets ?, ?. The class of all such aggregation operators is characterized by a lattice identity that they have to fulfill. In case of a unit interval we show the construction of aggregation operators preserving quasiconvexity from a pair of real valued functions on the unit interval. As a consequence we get that the intersection of quasiconvex fuzzy sets is quasiconvex if and only if the intersection is based on the minimum triangular norm.
aggregation operators quasiconvexity convexity lattice valued fuzzy sets