The stacker-crane problem (SCP) is a sequencing problem, arising in scheduling and transportation, that consists of finding the minimum cost cycle on a mixed graph with oriented arcs and unoriented edges: feasible sol...
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The stacker-crane problem (SCP) is a sequencing problem, arising in scheduling and transportation, that consists of finding the minimum cost cycle on a mixed graph with oriented arcs and unoriented edges: feasible solutions must traverse all the arcs. Approximation algorithms are known to provide a fixed worst-case bound if the triangle inequality holds. We consider the worst-case performance of approximation algorithms for the SCP when the triangle inequality can be violated (General SCP) and for a similar problem formulated on a complete digraph (Asymmetric SCP). (C) 1999 Elsevier Science B.V. All rights reserved.
In recent years there has been a trend towards large-scale logistics for individual members of the public, such as ride-sharing services and drone package delivery. Efficient coordination of pickups and deliveries is ...
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In recent years there has been a trend towards large-scale logistics for individual members of the public, such as ride-sharing services and drone package delivery. Efficient coordination of pickups and deliveries is essential in order to keep costs and wait times down.
In this thesis we present these types of problems in a more general framework, expanding applicability of our discussion to an even wider domain of problems. We present fast new al- gorithms with supporting theoretical and experimental analysis, providing certain guarantees about how close our algorithms compare to a theoretically optimal approach.
We consider the following optimisation problem that we encountered during the consolidation process of trains in a container transhipment terminal as well as in the intermediate storage of containers in sea ports in o...
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We consider the following optimisation problem that we encountered during the consolidation process of trains in a container transhipment terminal as well as in the intermediate storage of containers in sea ports in order to accelerate the loading and unloading of the vessels. There are n ordered pairs of points in the ni-dimensional metric space: (a(i), b(i)), 1 <= i <= n. The problem is to find a permutation i(1), i(2), ... , i(n) of numbers 1, 2, ... , n minimising the function Sigma(n-1)(j=1) d(b(ij), a(ij+1)) + d(b(in), a(i1)), where d(.,.) is the metric of the space. The problem can be considered as a special case of the asymmetric travelling salesman problem. As for Euclidean, Manhattan and Chehyshev metric the problem is NP-hard (as a generalisation of the well-known TSP problem) we propose the simple approximation algorithm with the approximation guarantee equal to 3. The approximation guarantee is tight as will be shown by a sequence of instances for which the approximation ratio converges to 3.
Several polynomial time approximation algorithms for some NPNPNP-complete routing problems are presented, and the worst-case ratios of the cost of the obtained route to that of an optimal are determined. A mixed-strat...
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Several polynomial time approximation algorithms for some NP-complete routing problems are presented, and the worst-case ratios of the cost of the obtained route to that of an optimal are determined. A mixed-strategy heuristic with a bound of 9/5 is presented for the stacker-crane problem (a modified traveling salesman problem). A tour-splitting heuristic is given for k-person variants of the traveling salesman problem, the Chinese postman problem, and the stacker-crane pr
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