Optimization of Order Quantity for Multi-Product from Multi-Supplier with Discounted Prices

Many researches in inventory control area of knowledge have been focused on single objective and multi-objective problem of determining the economic quantity of order. In single objective problems, costs were considered as the objective. However, multi-objective problems have not been well investigated. For instance, there are no hint to transportation cost, budget, or holding costs, or only capacity and demand constraints have been considered in these researches. This study focuses on developing a model accompanied by costs, quality and the time of delivery.The economic order quantity of multi-product from multi-supplier in multi-period under uncertainty in demand and discounted prices are considered in this paper. In first step, a mathematical model is developed for this problem. This mathematical model is solved by using multi-objective optimization method i.e. goal programming. Then, a meta-heuristic method based on multiobjective particle swarm optimization is proposed. Results of the small size numerical examples show that solutions found by using the proposed meta-heuristic method are in average, 5% worse than solutions found by using the mathematical methods; however, it needs much lower computational time.