Bipolar fuzzy graphs

In 1994, Zhang (Proceedings of FUZZ-IEEE, 1998) [195], (Proceedings of IEEE conference, 1994) [71] introduced the concept of bipolar fuzzy sets as a generalization of the notion of Zadeh’s fuzzy sets. A bipolar fuzzy subset of a set is a pair of functions one from the set into the interval [0, 1] and the other into the interval [ - 1, 0 ]. In a bipolar fuzzy set, the membership degree 0 of an element can be interpreted that the element is irrelevant to the corresponding property, the membership degree in (0, 1] of an element indicates the intensity that the element satisfies the property, and the membership degree in [ - 1, 0) of an element indicates the element does not satisfy the property. Fuzzy and possibilistic formalisms for bipolar information have been proposed in Dubios et al. Inf Pro Man Unc IPMU’04, 2002, [71] because bipolarity exists when dealing with spatial information in image processing or in spatial reasoning applications.