where (x1,x1,…,xn) is a vector of non-fuzzy decision variables,ecj is coefficient
in the objective; eai j; ebi are fuzzy coefficients in the constraints;
Cr represents credibility level; i and j represent the index
of the constraint decision variables, respectively. Formula (1a) is
the objective function to be optimized. Formula (1b) shows that
the credibility of constraint (∑
n
j¼1
eai jxj ≤ebi) should be greater than or
equal to level λi. Consider two fuzzy variables (ã and eb) with membership
function μ. The credibility of a fuzzy event, characterized by ea
≤eb, can be defined as follows