Abstract
One of the most important aspects in supply chain is how to purchase. In most purchasing literature, the problem of purchasing can be divided into two parts: the selection of suppliers and the quantity of ordering. Choosing a good supplier can not only reduce the purchasing cost but also guarantee the quality. Ordering a right quantity is equal to have lower inventory and ordering costs under the right price. However, today suppliers can not often satisfy all demands of a purchaser because of finite capacity so that the purchaser must order from multiple suppliers in different price. In this thesis, we use the traditional model of economic ordering quantity as the foundation and consider the multi-item, multi-supplier, finite capacity and price discount to propose a unified model for both of the supplier selection and the ordering quantity. In addition, the two-stage method is presented and compared with the software package, LINGO, to show that it is easy to find a near-optimal solution. Finally, we apply the two-stage method to test the fixed cycle approach and the independent cycle in the proposed model respectively. According to the computational results, the fixed cycle approach is more cost-effective than the independent cycle approach, especially in high price discount rate and high constraint tightness.