Despite more than a decade of experimental work in multi-robot systems, important theoretical aspects of multi-robot coordination mechanisms have, to date, been largely untreated. To address this issue, we focus on the problem of multi-robot task allocation (MRTA). Most work on MRTA has been ad hoc and empirical, with many coordination architectures having been proposed and validated in a proof-of-concept fashion, but infrequently analyzed. With the goal of bringing objective grounding to this important area of research, we present a formal study of MRTA problems. A domain-independent taxonomy of MRTA problems is given, and it is shown how many such problems can be viewed as instances of other, well-studied, optimization problems. We demonstrate how relevant theory from operations research and combinatorial optimization can be used for analysis and greater understanding of existing approaches to task allocation, and show how the same theory can be used in the synthesis of new approaches.

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A Formal Analysis and Taxonomy of Task Allocation in Multi-Robot Systems

The vehicle routing problem with time windows VRPTW is a generalization of the vehicle routing problem where the service of a customer can begin within the time window defined by the earliest and the latest times when the customer will permit the start of service. In this paper, we present the development of a new optimization algorithm for its solution. The LP relaxation of the set partitioning formulation of the VRPTW is solved by column generation. Feasible columns are added as needed by solving a shortest path problem with time windows and capacity constraints using dynamic programming. The LP solution obtained generally provides an excellent lower bound that is used in a branch-and-bound algorithm to solve the integer set partitioning formulation. Our results indicate that this algorithm proved to be successful on a variety of practical sized benchmark VRPTW test problems. The algorithm was capable of optimally solving 100-customer problems. This problem size is six times larger than any reported to date by other published research.

A new optimization algorithm for the vehicle routing problem with time windows

An algorithm is described for solving large-scale instances of the Symmetric Traveling Salesman Problem (STSP) to optimality. The core of the algorithm is a “polyhedral” cutting-plane procedure that exploits a subset of the system of linear inequalities defining the convex hull of the incidence vectors of the hamiltonian cycles of a complete graph. The cuts are generated by several identification procedures that have been described in a companion paper. Whenever the cutting-plane procedure does not terminate with an optimal solution the algorithm uses a tree-search strategy that, as opposed to branch-and-bound, keeps on producing cuts after branching. The algorithm has been implemented in FORTRAN. Two different linear programming (LP) packages have been used as the LP solver. The implementation of the algorithm and the interface with one of the LP solvers is described in sufficient detail to permit the replication of our experiments. Computational results are reported with up to 42 STSPs with sizes rangin...

A branch-and-cut algorithm for the resolution of large-scale symmetric traveling salesman problems

A New Optimization Algorithm for the Vehicle Routing Problem with Time Windows

Routing and scheduling of vehicles and crews: The state of the art

XMP is a hierarchically structured library of FORTRAN subroutines for linear programming. Its purpose is to facilitate algorithmic research and model development in operations research and related disciplines. The intended audience for XMP, the design goals that were identified as essential for serving that audience, and the way in which those goals were embodied in a working system, are described. Experience with XMP shows that an LP system can be designed primarily for flexibility and ease of modification without too great a sacrifice in computational efficiency.

The Design of the XMP Linear Programming Library

The set partitioning model of the crew rotation problem has been well known for many years. This paper focuses on recent developments that have made this model more attractive and have resulted in several successful implementations. These developments include improved problem conceptualizations and decompositions, as well as new solution techniques employing Lagrangian relaxation and subgradient optimization. Experience is reported from The Flying Tiger Line, Pacific Southwest Airways, Continental Airlines, and Helsinki City Transport. A case is made for work on heuristic decomposition methods to break large problems into moderate sized pieces that can be solved exactly.

Exact solution of crew scheduling problems using the set partitioning model: Recent successful applications

The dynamic programming and branch-and-bound approaches are combined to produce a hybrid algorithm for separable discrete mathematical programs. Linear programming is used in a novel way to compute bounds. Every simplex pivot permits a bounding test to be made on every active node in the search tree. Computational experience is reported.

A hybrid approach to discrete mathematical programming

This paper deals with the mathematical programming aspects of a long range planning study done for the Flying Tiger Line, an all-cargo airline. The study addressed two strategic problems: the design of the service network and the selection and deployment of the aircraft fleet. We show how the concept of a spider graph provides a natural building block for network design and present a mixed-integer programming model that enables the planner to evaluate any network constructed from spider graphs by determining the most profitable selection of aircraft and routing of cargo.

Roy E. Marsten

Papers

The Design of the XMP Linear Programming Library

Exact solution of crew scheduling problems using the set partitioning model: Recent successful applications

A hybrid approach to discrete mathematical programming

A Mixed-Integer Programming Approach to Air Cargo Fleet Planning