An Inventory System with Postponed Demands

Abstract

In this article we consider a continuous review perishable inventory system in which the demands arrive according to a Markovian arrival process (MAP). The items in the inventory have shelf life times that are assumed to follow an exponential distribution. The inventory is replenished according to an (s, S) policy and the replenishing times are assumed to follow a phase type distribution. The demands that occur during stock out periods either enter a pool which has capacity N (<∞) or leave the system. Any demand that arrives when the pool is full and the inventory level is zero, is also assumed to be lost. The demands in the pool are selected one by one, if the replenished stock is above s, with interval time between any two successive selections is distributed as exponential with parameter depending on the number of customers in the pool. The joint probability distribution of the number of customers in the pool and the inventory level is obtained in the steady state case. The measures of system performance in the steady state are derived and the total expected cost rate is also calculated. The results are illustrated numerically.

Keywords:

• Continuous review
• Markovian arrival process
• Postponed demands
• (s, S) policy

AMS Subject Classification:

• 90B05
• 60J27

Acknowledgments

The research was supported by National Board for Higher Mathematics, India, research award 48/3/2004/R&D-II/2114.

We wish to thank the anonymous referees for their valuable suggestions which have improved the presentation of this article.