Asia-Pacific Journal of Operational Research

In this paper we describe a genetic algorithm (GA) for the uncapacitated multiple allocation p-hub center problem (UMApHCP). Binary coding is used and genetic operators adapted to the problem are constructed and implemented in our GA. Computational results are presented for the standard hub instances from the literature. It can be seen that proposed GA approach reaches all solutions that are proved to be optimal so far. The solutions are obtained in a reasonable amount of computational time, even for problem instances of higher dimensions.

We extend the two similar interior-point approaches to sensitivity analysis originally developed for linear programs to those for convex quadratic programs, where the first approach is the ∊-sensitivity analysis and the other is Yildirim and Todd's. We study the relationship between the bounds on perturbation of the input parameters arising from the extension of Yildirim and Todd's approach and those from the ∊-sensitivity analysis. Furthermore, we prove that Yildirim and Todd's bounds are asymptotically the same as the symmetrized optimal tripartition bounds in the case of a special type of nondegeneracy.

A large number of products are now being sold with long-term warranty policies. This is mainly due to fierce competition in the market and customer demand. Offering long-term warranty results in additional complexities in estimating costs associated with warranty servicing due to the uncertainties associated with usage, preventive maintenance and warranty servicing strategies. This paper reviews various long-term warranty policies and mathematical models for estimation of warranty servicing costs.

In this paper, we extend a class of merit functions proposed by Kanzow et al. (1997) for linear/nonlinear complementarity problems to Symmetric Cone Complementarity Problems (SCCP). We show that these functions have several interesting properties, and establish a global error bound for the solution to the SCCP as well as the level boundedness of every merit function under some mild assumptions. Moreover, several functions are demonstrated to enjoy these properties.

This paper considers a two commodity continuous review inventory system. The demand points for each commodity are assumed to form Poisson processes. It is further assumed that the demand for the first commodity require the one unit of second commodity in addition to the first commodity with probability p₁. Similarly, the demand for the second commodity require the one unit of first commodity in addition to the second commodity with probability p₂. This assumption model the situation in which a buyer who intends to buy one particular commodity may also go for another commodity. The limiting probability distribution for the joint inventory levels is computed. Various operational characteristics, expression for the long run total expected cost rate is derived. The results are illustrated with numerical examples.

An attempt is made to formulate optimal ordering policies for the retailer when the supplier offers progressive credit periods to settle the account. We define progressive credit periods as follows: If the retailer settles the outstanding amount by M, the supplier does not charge any interest. If the retailer pays after M but before N(M < N), then the supplier charges the retailer on the un-paid balance at the rate Ic₁. If the retailer settles the account after N, then he will have to pay an interest rate of Ic₂ (Ic₂ > Ic₁). The objective function to be optimized is considered as present value of all future cash-out-flows. An algorithm is given to find the flow of optimal ordering policy. Analytic proofs are discussed to study the effect of various parameters on an objective function.

In this paper, the so-called η-approximation approach is used to obtain the sufficient conditions for a nonlinear multiobjective programming problem with univex functions with respect to the same function η. In this method, an equivalent η-approximated vector optimization problem is constructed by a modification of both the objective and the constraint functions in the original multiobjective programming problem at the given feasible point. Moreover, to find the optimal solutions of the original multiobjective problem, it sufficies to solve its associated η-approximated vector optimization problem. Finally, the description of the η-approximation algorithm for solving a nonlinear multiobjective programming problem involving univex functions is presented.

We consider a single-period distribution system with one supplier and two retailers. The supplier may have infinite or finite capacity. The demand at each retailer is random. When a stockout occurs at one retailer the customer may go to the other retailer. We study both the decentralized and centralized inventory control problems. For the decentralized problem we show that a unique Nash equilibrium exists when the capacity at the supplier is infinite. However, when the capacity is finite, only under certain conditions does the Nash equilibrium exist. For centralized inventory control we obtain the optimal allocation that maximizes the expected profit of the entire supply chain. For the case of decentralized controls we also design channel coordination mechanisms, i.e., a decentralized cost structure resulting in a Nash equilibrium with chain-wide profits equal to those achieved under a fully centralized system. We compare the performance of two retailers in the decentralized and centralized controls and analyze the impact of channel coordination on the whole supply chain.