Fuzzy inventory model for deteriorating items with permissible delay in payment

In this paper, we extend the model of Jamal et al. by fuzzifying the carrying cost rate, interest paid rate and interest earned rate simultaneously, based on the interval-valued fuzzy numbers and triangular fuzzy number to fit the real world. We then prove that the estimate of total variable cost per unit time in the fuzzy sense is a strictly pseudo-convex function. As a result, there exists a unique optimal solution to our proposed model. Moreover, we apply the Jamal et al. example to show the results and to compare with the model of Jamal et al.