292 research outputs found
Operational Research: Methods and Applications
Throughout its history, Operational Research has evolved to include a variety of methods, models and algorithms that have been applied to a diverse and wide range of contexts. This encyclopedic article consists of two main sections: methods and applications. The first aims to summarise the up-to-date knowledge and provide an overview of the state-of-the-art methods and key developments in the various subdomains of the field. The second offers a wide-ranging list of areas where Operational Research has been applied. The article is meant to be read in a nonlinear fashion. It should be used as a point of reference or first-port-of-call for a diverse pool of readers: academics, researchers, students, and practitioners. The entries within the methods and applications sections are presented in alphabetical order. The authors dedicate this paper to the 2023 Turkey/Syria earthquake victims. We sincerely hope that advances in OR will play a role towards minimising the pain and suffering caused by this and future catastrophes
Stochastic Model Predictive Control for Autonomous Mobility on Demand
This paper presents a stochastic, model predictive control (MPC) algorithm
that leverages short-term probabilistic forecasts for dispatching and
rebalancing Autonomous Mobility-on-Demand systems (AMoD, i.e. fleets of
self-driving vehicles). We first present the core stochastic optimization
problem in terms of a time-expanded network flow model. Then, to ameliorate its
tractability, we present two key relaxations. First, we replace the original
stochastic problem with a Sample Average Approximation (SAA), and characterize
the performance guarantees. Second, we separate the controller into two
separate parts to address the task of assigning vehicles to the outstanding
customers separate from that of rebalancing. This enables the problem to be
solved as two totally unimodular linear programs, and thus easily scalable to
large problem sizes. Finally, we test the proposed algorithm in two scenarios
based on real data and show that it outperforms prior state-of-the-art
algorithms. In particular, in a simulation using customer data from DiDi
Chuxing, the algorithm presented here exhibits a 62.3 percent reduction in
customer waiting time compared to state of the art non-stochastic algorithms.Comment: Submitting to the IEEE International Conference on Intelligent
Transportation Systems 201
A* search algorithm for an optimal investment problem in vehicle-sharing systems
We study an optimal investment problem that arises in the context of the
vehicle-sharing system. Given a set of locations to build stations, we need to
determine i) the sequence of stations to be built and the number of vehicles to
acquire in order to obtain the target state where all stations are built, and
ii) the number of vehicles to acquire and their allocation in order to maximize
the total profit returned by operating the system when some or all stations are
open. The profitability associated with operating open stations, measured over
a specific time period, is represented as a linear optimization problem applied
to a collection of open stations. With operating capital, the owner of the
system can open new stations. This property introduces a set-dependent aspect
to the duration required for opening a new station, and the optimal investment
problem can be viewed as a variant of the Traveling Salesman Problem (TSP) with
set-dependent cost. We propose an A* search algorithm to address this
particular variant of the TSP. Computational experiments highlight the benefits
of the proposed algorithm in comparison to the widely recognized Dijkstra
algorithm and propose future research to explore new possibilities and
applications for both exact and approximate A* algorithms.Comment: Full version of the conference paper which is accepted to be appear
in the proceeding of the The 12th International Conference on Computational
Data and Social Networks - SCONET202
Fast Evaluation of Ensemble Transients of Large IP Networks
We extend a numerical approximate solution method (the Z-iteration)
to time-dependent open networks of
M(t)/M(t)/1/ and M(t)/M(t)/1/K queues,
and apply the method to obtain transient performance metrics
of large IP networks.
The method generates a set of coupled differential equations,
one for each queue in the network.
The equations are numerically unstable under certain conditions
(e.g., large bandwidths and buffers),
and we present techniques to overcome this problem.
The resulting numerical procedure is accurate and very fast.
For example,
a 20-second evolution for a 1000-node network with
high-speed links (packets/sec)
and large buffers (packets)
was obtained in 18 minutes on an Ultra Sparc,
whereas simulation would take days
- …