We introduce a generic propagation mechanism for constraint programming. The method is based on the results of matching theory which is a mature and well-studied subject of graph theory. A first benefit of our new pru...
详细信息
We introduce a generic propagation mechanism for constraint programming. The method is based on the results of matching theory which is a mature and well-studied subject of graph theory. A first benefit of our new pruning technique comes from the fact that it can be applied on several global constraints whose solution is representable by a matching in a particular graph. In this work we describe a filtering scheme for such a family based on the Gallai-Edmonds Structure Theorem. In a number of important cases our method achieves hyper-arc consistency in polynomial time.
In this paper we present two type extensions for the modeling language MINIZINC that allow the representation of some problems in a more natural way. The first proposal, called MINIZINC, extends existing types with ad...
详细信息
In this paper we present two type extensions for the modeling language MINIZINC that allow the representation of some problems in a more natural way. The first proposal, called MINIZINC, extends existing types with additional values. The user can specify both the extension of a predefined type with new values, and the behavior of the operations with relation to the new types. We illustrate the usage of MINIZINC* to model SQL-like problems with integer variables extended with NULL values. The second extension, MINIZINC(+), introduces union types in the language. This allows defining recursive types such as trees, which are very useful for modeling problems that involve complex structures. A new case statement is introduced to select the different components of union type terms. The paper shows how a model defined using these extensions can be transformed into a MINIZINC model which is equivalent to the original model. (C) 2015 Elsevier B.V. All rights reserved.
In this paper, the problem of balancing and cyclic scheduling of flexible mixed model assembly lines with parallel stations is studied. To exploit the connection between balancing and cyclic scheduling problems for an...
详细信息
In this paper, the problem of balancing and cyclic scheduling of flexible mixed model assembly lines with parallel stations is studied. To exploit the connection between balancing and cyclic scheduling problems for an efficient line management, they are considered simultaneously. A novel constraint programming model including problem specific symmetry breaking constraints is proposed to solve this problem. Experiments on extensive number of test instances with various sizes are also presented. (C) 2015 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.
Local branching is a general purpose heuristic method which searches locally around the best known solution by employing tree search. It has been successfully used in Mixed Integer programming (MIP) where local branch...
详细信息
ISBN:
(纸本)9783939897170
Local branching is a general purpose heuristic method which searches locally around the best known solution by employing tree search. It has been successfully used in Mixed Integer programming (MIP) where local branching constraints are used to model the neighborhood of an incumbent solution and improve the bound. The neighborhoods are obtained by linear inequalities in the MIP model so that MIP searches for the optimal solution within the Hamming distance of the incumbent solution. The linear constraints representing the neighborhood of incumbent solutions are called local branching constraints and are involved in the computation of the problem bound. Local branching is a general framework to effectively explore solution subspaces, making use of the state-of-the-art MIP solvers.
This paper presents a novel method of designing selected aspects of messaging-based integration solutions. The method uses constraint programming to find appropriate communication channels, components' deployment ...
详细信息
ISBN:
(纸本)9783642155758
This paper presents a novel method of designing selected aspects of messaging-based integration solutions. The method uses constraint programming to find appropriate communication channels, components' deployment parameters and integration services in order to create a solution that meets specified functional and non-functional requirements. The method has been evaluated using a prototype implementation and compared to authors' earlier work that used action-based planning techniques to reach similar goals.
Although sometimes it is necessary, no one likes to stay in a hospital, and patients who need to stay in bed but do not require constant medical surveillance prefer their own bed at home. At the same time, a patient i...
详细信息
Although sometimes it is necessary, no one likes to stay in a hospital, and patients who need to stay in bed but do not require constant medical surveillance prefer their own bed at home. At the same time, a patient in a hospital has a high cost for the community, that is not acceptable if the patient needs service only a few minutes a day. For these reasons, the current trend in Europe and North-America is to send nurses to visit patients at their home: this choice reduces costs for the community and gives better quality of life to patients. The challenge is to deliver the service in a cost effective manner without a detriment of the service quality. These social and health management issues have interesting implications from the mathematical viewpoint, introducing a challenging combinatorial optimization problem. The problem consists in assigning patients' services to traveling nurses and defining the nurse itineraries so that the following optimization aspects are considered: the nurse workloads (including service as well as travel time) are balanced, patients are preferentially served by a single nurse or just a few ones, and the overall travel time is minimized. These objectives are somehow conflicting and a reasonable trade off must be found. The complexity of the problem calls for suitable optimization-based algorithmic support to decisions, in particular in the perspective of an increasing diffusion of the service. This problem is known in the literature as the Home Health Care (HHC) problem. In this paper, we address the HHC problem in the municipality of Ferrara, a mid-sized city in the North of Italy. The problem is currently solved by hand, starting from a partitioning of patients based on predefined zones. We describe a constraint programming model that solves the HHC problem, and show significant improvements with respect to the current manual solution.
Symmetry breaking has been a hot topic of research in the past years, leading to many theoretical developments as well as strong scaling strategies for dealing with hard applications. Most of the research has however ...
详细信息
Symmetry breaking has been a hot topic of research in the past years, leading to many theoretical developments as well as strong scaling strategies for dealing with hard applications. Most of the research has however focused on discrete, combinatorial, problems, and only few considered also continuous, numerical, problems. While part of the theory applies in both contexts, numerical problems have specificities that make most of the technical developments inadequate. In this paper, we present the ALEX constraints, partial symmetry-breaking inequalities corresponding to a relaxation of the famous LEx constraints extensively studied in the discrete case. They allow (partially) breaking any variable symmetry and can be generated in polynomial time. Contrarily to LEX constraints that are impractical in general (due to their overwhelming number) and inappropriate in the continuous context (due to their form), RLEX constraints can be efficiently handled natively by numerical constraint solvers. Moreover, we demonstrate their pruning power on continuous domains is almost as strong as that of LEX constraints, and they subsume several previous work on breaking specific symmetry classes for continuous problems. Their experimental behavior is assessed on a collection of standard numerical problems and the factors influencing their impact are studied. The results confirm ALEX constraints are a dependable counterpart to LEX constraints for numerical problems. (C) 2015 Elsevier B.V. All rights reserved.
Energy efficiency has become a primary goal to be pursued for sustainable logistics. In automated storage and retrieval systems this leads to revise the traditional control policies aimed at picking time minimisation ...
详细信息
Energy efficiency has become a primary goal to be pursued for sustainable logistics. In automated storage and retrieval systems this leads to revise the traditional control policies aimed at picking time minimisation and to pay more attention to rack configuration, which has been not a research concern from the time-based perspective. Proper models for energy calculation should be developed by introducing new factors neglected in time analysis, such as the weight of unit loads and the differentiation of shifts along the horizontal and vertical axis as regard energy requirements, due to different contribution of gravity, inertia and friction. In this study, a classification of racks based on system height is proposed in order to select the proper crane specifications needed to compute the torque to be overcome by motors to serve a given location within a rack. An overall optimisation model based on constraint programming hybridised with Large Neighborhood Search is developed, allowing the joint application of the best control policies for storage assignment and sequencing both for time and energy-based optimisation, as well as the introduction of multiple weight unit loads and energy recovery. Simulations analysis is performed in order to assess the impact of the rack shape on energy saving. Results show how, regardless the demand curve and the optimisation objective, the best performances in terms of energy efficiency are reached by the intermediate height rack shapes, while the lower ones outperform when considering travel time performance.
To maintain an energy footprint as low as possible, data centres manage their VMs according to conventional and established rules. Each data centre is however made unique due to its hardware and workload specificities...
详细信息
To maintain an energy footprint as low as possible, data centres manage their VMs according to conventional and established rules. Each data centre is however made unique due to its hardware and workload specificities. This prevents the ad hoc design of current VM managers from taking these particularities into account to provide additional energy savings. In this paper, we present Plug4Green, an energy-aware VM placement algorithm that can be easily specialized and extended to fit the specificities of the data centres. Plug4Green computes the placement of the VMs and state of the servers depending on a large number of constraints, extracted automatically from SLAs. The flexibility of Plug4Green is achieved by allowing the constraints to be formulated independently from each other but also from the power models. This flexibility is validated through the implementation of 23 SLA constraints and 2 objectives aiming at reducing either the power consumption or the greenhouse gas emissions. On a heterogeneous test bed, Plug4Green specialization to fit the hardware and the workload specificities allowed to reduce the energy consumption and the gas emission by up to 33% and 34%, respectively. Finally, simulations showed that Plug4Green is capable of computing an improved placement for 7500 VMs running on 1500 servers within a minute. (C) 2014 Elsevier B.V. All rights reserved.
Optimization plays an important role in various disciplines of engineering. Multi-objective optimization is usually characterized by a Pareto front. In large scale multiobjective optimization problems, determining an ...
详细信息
ISBN:
(纸本)9781509018987
Optimization plays an important role in various disciplines of engineering. Multi-objective optimization is usually characterized by a Pareto front. In large scale multiobjective optimization problems, determining an optimal Pareto front consumes large time. Thus, parallel computing is used to speed up the search. constraint programming is one of the logic-based optimization techniques for solving combinatorial optimization problems. In our previous study, we proposed the multi-objective embarrassingly parallel search (MO-EPS) for multi-objective constraint optimization, which combines two strategies: a constraint programmingbased strategy to determine Pareto front and a parallel search for constraint programming. In this study, we propose the MO-EPS with upper bound constraints, an extended algorithm of the MO-EPS.
暂无评论