An Improved Algorithm for Fixed-Hub Single Allocation Problem

This paper discusses the fixed-hub single allocation problem (FHSAP). In this problem, a network consists of hub nodes and terminal nodes. Hubs are fixed and fully connected; each terminal node is connected to a single hub which routes all its traffic. The goal is to minimize the cost of routing the traffic in the network. In this paper, we propose a linear programming (LP)-based rounding algorithm. The algorithm is based on two ideas. First, we modify the LP relaxation formulation introduced in Ernst and Krishnamoorthy (1996, 1999) by incorporating a set of validity constraints. Then, after obtaining a fractional solution to the LP relaxation, we make use of a geometric rounding algorithm to obtain an integral solution. We show that by incorporating the validity constraints, the strengthened LP often provides much tighter upper bounds than the previous methods with a little more computational effort, and the solution obtained often has a much smaller gap with the optimal solution. We also formulate a robust version of the FHSAP and show that it can guard against data uncertainty with little cost

Life-Cycle Models: Lifetime Earnings and the Timing of Retirement

After dropping for a century, the average retirement age for U.S. males seems to have leveled off in recent decades. An important question is whether as future improvements in technology cause wages to rise, desired retirement ages will resume their downward trend, or not. This paper attempts to use HRS panel data to test how relatively high (or low) earnings affect male retirement ages. Our goal is to use cross-sectional earning differences to help anticipate likely time-series developments in coming decades. Our preliminary regression results show that higher earnings do lead to somewhat earlier retirement. Unless additional analysis changes the parameter estimates, the implication is that the downward trend in male retirement ages will ultimately return.

A regret model applied to the facility location problem with limited capacity facilities

This article addresses issues related to location and allocation problems. Herein, we intend to demonstrate the influence of congestion, through the random number generation, of such systems in final solutions. An algorithm is presented which, in addition to the GRASP, incorporates the Regret with the pminmax method to evaluate the heuristic solution obtained with regard to its robustness for different scenarios. Taking as our point of departure the Facility Location Problem proposed by Balinski [27], an alternative perspective is added associating regret values to particular solutions.N/