This article traces the evolution of ambulance location and relocation models proposed over the past 30 years. The models are classified in two main categories. Deterministic models are used at the planning stage and ignore stochastic considerations regarding the availability of ambulances. Probabilistic models reflect the fact that ambulances operate as servers in a queueing system and cannot ...

We consider a model of nomadic agents exploring and competing for time-varying location-specific resources, arising in crowdsourced transportation services, online communities, and in traditional locationbased economic activity. This model comprises a group of agents, and a set of locations each endowed with a dynamic stochastic resource process. Each agent derives a periodic reward determined ...

Available online 6 October 2008

future increase of mobile communication subscribers will require a great capacity expansion of the cellular systems. in order to accommodate the increasing number of subscribers, the cell size will have to be much smaller than current size. therefore, it is predictable that the location updating and paging procedures will produce a major part of signaling traffic in these networks. this pape...

Many real world problems involve making repeated decisions over time in an uncertain environment. These decisions often involve a trade-off between some immediate benefit(s) and possible future benefit(s), and also take in to account the impact the decision will have on future decisions and benefits. Stochastic dynamic programming (SDP) is often used to analyse problems of this type and the obj...

The two most widely considered measures for optimization under uncertainty are minimizing expected cost and minimizing worst-case cost or regret. In this paper, we present a novel robustness measure that combines the two objectives by minimizing the expected cost while bounding the relative regret in each scenario. In particular, the models seek the minimum-expected-cost solution that is p-robu...

generally ordering policies are done by two methods, including fix order quantity (foq) and fix order period (fop). these methods are static and either the quantity of ordering or the procedure of ordering is fixing in throughout time horizon. in real environments, demand is varying in any period and may be considered as uncertainty. when demand is variable in any period, the traditional and st...

The hub location–allocation problem under uncertainty is a real-world task arising in the areas such as public and freight transportation and telecommunication systems. In many applications, the demand is considered as inexact because of the forecasting inaccuracies or human’s unpredictability. This study addresses the robust uncapacitated multiple allocation hub location problem with a set of ...

In the context of public transportation system, improving the service quality and robustness through minimizing the average passengers waiting time is a real challenge. This study provides robust stochastic programming models for train timetabling problem in urban rail transit systems. The objective is minimization of the weighted summation of the expected cost of passenger waiting time, its va...