Then the incremental quantity discounts was taken into account and a PSO-based algorithm was developed to obtain the optimal (R, Q) policy and selection supplier for the buyer.

The new JIT purchasing model is discussed respectively with all unit quantity discounts and incremental quantity discounts, also the paper gives the algorithm and example for the model.

In multi-item ordering problems with fund constraint, when the supplier offers incremental quantity discounts, the retailer will adjust the inventory policy to minimize the inventory cost.