We introduce a novel and exciting research area: symmetrising levels of consistency to produce stronger forms of consistency and more efficient mechanisms for establishing them. We propose new levels of consistency fo...
详细信息
Many symmetry breaking techniques assume thai;the symmetries of a CSP are given as input in addition to the CSP itself. We present a method that can be used to detect all the symmetries of a CSP. this method construct...
详细信息
When the search for a solution to a constraint satisfaction problem backtracks, it is not usually worthwhile to remember the assignment that failed, because the same assignment will not occur again. However, we show t...
详细信息
constraints and preferences are ubiquitous in real-life. Moreover, preferences can be of many kinds: qualitative, quantitative, conditional, positive or negative, to name a few. Our ultimate goal is to define and stud...
详细信息
Graphical models are a powerful representation framework for automated reasoning tasks. these models use graphs to capture conditional independencies between variables, allowing for a concise representation of the kno...
详细信息
ISBN:
(纸本)3540292381
Graphical models are a powerful representation framework for automated reasoning tasks. these models use graphs to capture conditional independencies between variables, allowing for a concise representation of the knowledge. Optimization tasks defined within this framework are typically tackled with either search or inference. Search methods are time exponential in the number of variables and can operate in linear space. Inference algorithms are time and space exponential in the tree width of the problem. this potentially higher space complexity makes these methods impractical. the AND/OR search space for graphical models is a newly introduced framework for search that is sensitive to the independencies in the model, often resulting in exponentially reduced complexities. the AND/OR search is based on a pseudo-tree which expresses independencies between variables, resulting in a search tree exponential in the depth of the pseudo-tree, rather than the number of variables. the AND/OR Branch-and-Bound algorithm (AOBB) is a new search method that explores the AND/OR search tree for solving optimization tasks in graphical models. In this paper we extend the algorithm for solving combinatorial optimization problems from the class of Mixed Integer Linear Programs (MILP). A MILP instance is a linear program where some of the decision variables are constrained to have only integer values at the optimal solution (we consider only binary integer variables). AOBB can be readily adapted for solving this class of optimization problems by arranging the integer variables into a start pseudo-tree and, then, traversing the corresponding AND/OR search tree. this rather straightforward extension can be further improved. We introduce a dynamic version of AOBB which uses a recursive decomposition of the problem, based on hypergraph separators. the hypergraph of a MILP instance has a vertex for each constraint and a hyperedge, which corresponds to a variable, connects all the constraints t
the heavy-tailed phenomenon that characterises the runtime distributions of backtrack search procedures has received considerable attention over the past few years. Some have conjectured that heavy-tailed behaviour is...
详细信息
ISBN:
(纸本)3540292381
the heavy-tailed phenomenon that characterises the runtime distributions of backtrack search procedures has received considerable attention over the past few years. Some have conjectured that heavy-tailed behaviour is largely due to the characteristics of the algorithm used. Others have conjectured that problem structure is a significant contributor. In this paper we attempt to explore the former hypothesis, namely we study how variable and value ordering heuristics impact the heavy-tailedness of runtime distributions of backtrack search procedures. We demonstrate that heavy-tailed behaviour can be eliminated from particular classes of random problems by carefully selecting the search heuristics, even when using chronological backtrack search. We also show that combinations of good search heuristics can eliminate heavy tails from Quasigroups with Holes of order 10, and give some insights into why this is the case. these results motivate a more detailed analysis of the effects that variable and value ordering can have on heavy-tailedness. We show how combinations of variable and value ordering heuristics can result in a runtime distribution being inherently heavytailed. Specifically, we show that even if we were to use an Oracle to refute insoluble subtrees optimally, for some combinations of heuristics we would still observe heavy-tailed behaviour. Finally, we study the distributions of refutation sizes found using different combinations of heuristics and gain some further insights into what characteristics tend to give rise to heavy-tailed behaviour.
the availability of commodity multiprocessors offers significant opportunities for addressing the increasing computational requirements of optimization applications. To leverage these potential benefits, it is importa...
详细信息
Distributed constraint satisfaction problems (DisCSPs) with asymmetric constraints reflect the fact that agents may wish to retain their constraints private. Brito and Meseguer proposed a model for asymmetric constrai...
详细信息
ISBN:
(纸本)3540292381
Distributed constraint satisfaction problems (DisCSPs) with asymmetric constraints reflect the fact that agents may wish to retain their constraints private. Brito and Meseguer proposed a model for asymmetric constraints which they term Partially Known constraints (PKC). In the PKC model each binary constraint is divided between the two constraining agents. In order to solve the resulting DisCSP with asymmetric constraints, a two phase asynchronous backtracking algorithm was proposed [?]. In the first phase an asynchronous backtracking algorithm is performed, in which only the constraints held by the lower priority agents are examined. When a solution is reached, a second phase is performed in which the consistency of the solution is checked again, according to the constraints held by the higher priority agents in each binary constraint. the present paper proposes a one phase asynchronous backtracking algorithm which solves DisCSPs with asymmetric constraints. In the proposed asynchronous backtracking for asymmetric constraints algorithm (ABT_ASC) agents send their proposed assignments to all their neighbors in the constraints graph. Agents assign their local variables according to the priority order as in ABT but check the constraints also against the assignment of lower priority agents. When an agent detects a conflict between its own assignment and the assignment of an agent with a lower priority than itself, it sends a Nogood to the lower priority agent but keeps its assignment. Agents which receive a Nogood from higher priority agents, perform the same operations as if they have produced this Nogood themselves. As in ABT [?], they remove their current assignment from their current-domain, store the eliminating N ogood and reassign their variable. the ABT_ASC algorithm is evaluated experimentaly on randomly generated DisCSPs and is shown to outperform the 2-phase ABT with respect to two different distributed performance measures. ABT_ASC performs fewer non-concu
Given a configuration of parameters that satisfies a set of constraints, and given external changes that change and fix the value of some parameters making the configuration invalid, the problem of interactive reconfi...
详细信息
the automatic modelling tool CONJURE [1] generates CSP models from a problem specified in the specification language ESSENCE1. Variables in ESSENCE may have domains currently unsupported by solvers. Also, the elements...
详细信息
暂无评论