Sains Malaysiana 41(4)(2012): 493-497

A Replenishment Inventory Model for Items Under Time-Varying Demand Rates

Considering Trade Credit Period and Cash Discount for a Finite Time Horizon

(Model Penambahan Inventori Bila Kadar Permintaan Berubah Terhadap Masa Dengan

Bayaran Tertangguh dan Diskaun Tunai Dibenarkan untuk Masa Terhingga)

Mohd Omar*

Institute of Mathematical Sciences, Faculty of Science, University of Malaya

50603 Kuala Lumpur, Malaysia

Diserahkan: 30 Jun 2011 / Diterima: 20 Oktober 2011

ABSTRACT

Many researchers have developed various economic ordering quantity models by assuming an infinite time horizon and constant demand rate. However due to rapid technological advancement, shorter product life cycle and severe competition, those assumptions are no longer realistic. In this paper, we complement that shortcoming by considering an inventory model that satisfies a continuous time-varying demand rate for a finite time horizon when trade credit period and unit cash discount are allowed. The time horizon consists of n different cycles with equal or different cycles length. The trade credit period was assumed to be proportional to the cycle length. We developed mathematical models and presented a numerical example to support the effectiveness of these models.

Keywords: Cash discount; delay payment; finite horizon; inventory; time-varying demand

ABSTRAK

Ramai penyelidik telah membangunkan pelbagai model Kuantiti Pesanan Ekonomi dengan andaian masa

perancangannya tak terhingga dan kadar permintaannya adalah tetap. Bagaimanapun perkembangan pesat teknologi, masa produk yang singkat dan persaingan yang hebat, andaian itu tidak lagi realistik. Kertas ini akan menghilangkan kekurangan itu dengan membina model inventori bila kadar permintaan berubah terhadap masa untuk masa terhingga bila bayaran tertangguh dan diskaun tunai dibenarkan. Masa perancangannya mengandungi n kitaran dengan tempoh yang sama atau berbeza. Tempoh bayaran tertangguh diandaikan berkadaran dengan tempoh bagi setiap kitaran.  Kami telah membina model matematiknya dan memberikan contoh berangka untuk menyokong keberkesanan model tersebut.

Kata kunci: Bayaran tertangguh; diskaun tunai; inventori; masa terhingga; permintaan berubah terhadap masa

RUJUKAN

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Goyal, S.K., 1985. Economic order quantity under conditions of permissible delay in payments. Journal of the Operational Research Society 36: 335-338.

Jamal, A.M.M., Sarker, B.R. & Wang, S. 1997. An ordering policy for deteriorating items with allowable shortage and permissible delay in payment. Journal of the Operational Research Society 48: 826-833.

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Ouyang, L.Y., Chen, M.S. & Chuang, K.W. 2002. Economic order quantity model under cash discount and payment delay. International Journal of Information and Management Sciences 13: 1-10.

*Pengarang untuk surat-menyurat; email: mohd@um.edu.my