عنوان مقاله [English]
In this research, we investigate the two-echelon single-period inventory problem, in which the raw materials and the final product should be provided at the beginning of the selling period. Raw materials that remain unused and the final products that remain unsold until the end of the period, can be sold at a discount at the end of the period. the use of coefficient in final products is different from each raw material, so the raw materials and the final product may not have a one-to-one relationship; we have a certain limited budget for buying the raw materials and producing the final products. Supplier will offer the discount for each raw material to reduce his inventory level, if we buy more than a certain quantity of that raw materials. Since the price of the final product at the end of the period is so Low, we set a cumulative discount policy to encourage customers for our final product. Consequently, one of the costumers buys more than acertain quantity, and the price of each final product for that costumer will be less than the normal price. If the final product is sold out during the period, depending on the demand, some of our customers will wait for transforming raw materials into the final product during the period. The objective of this problem is to find the order of quantities of both the raw materials and the final product, such that the expected profit can be maximized. A mathematical model was first developed for this problem, then a particle swarm optimization algorithm (PSO) was proposed to solve it. Finally, a numerical example was given to illustrate the application of the proposed methodology. This example was solved by the developed PSO algorithm, and to receive a better answer from PSO, we ran the algorithm 50 times.