ABSTRACT
Fuzzy set theory, proposed by Zadeh in 1965, takes into account membership degree and non-membership degree. Non-membership degree is the complement of membership degree. However, in real life, this linguistic negation does not satisfy the logical negation. The selection of membership degree depends on the user’s choice, which may be Gaussian, triangular, exponential or any other. There is an uncertainty involved in defining the membership function. This is the reason different results are obtained with different membership functions. Subsequently, Atanassov suggested an advanced fuzzy set, which is an intuitionistic fuzzy set (IFS). In this set, non-membership degree is not equal to the complement of the membership degree; rather, it is less than or equal to the complement of the membership degree, due to the uncertainty in defining the membership degree.
