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1.
Generalization of Clauses Relative to a Theory   总被引:1,自引:0,他引:1  
Plotkin's notions of relative -subsumption and relative least general generalization of clauses are defined for full clauses, and they are defined in terms of a kind of resolution derivations called C-derivations. Techniques for generalization of clauses relative to a theory, based on the V-operators or saturation in its original form, have primarily been developed for Horn clauses. We show that these techniques are incomplete for full clauses, which is due to the restricted form of resolution derivations considered. We describe a technique for generalization of clauses relative to a theory, which is based on a generalization of the original saturation technique. We prove that our technique properly inverts C-derivations, and that it is complete for full clauses w.r.t. relative -subsumption.  相似文献   

2.
为了有效管理学习子句,避免学习子句规模呈几何级增长,减少冗余学习子句对系统内存占用,从而提高布尔可满足性问题SAT求解器的求解效率,需要对学习子句进行评估,然后删减学习子句。传统的评估方式是基于学习子句的长度,保留较短的子句。当前主流的做法一个是变量衰减和VSIDS的子句评估方式,另外一个是基于文字块距离LBD的评估方式,也有将二者结合使用作为子句评估的依据。通过对学习子句参与冲突分析次数与问题求解的关系进行分析,将学习子句使用频率与LBD评估算法混合使用,既反映了学习子句在冲突分析中的作用,也充分利用了文字与决策层之间的信息。以Syrup求解器(GLUCOSE 4.1并行版本)为基准,在评估算法与并行子句共享策略方面做改进测试,通过实验对比发现,混合评估算法比LBD评估算法有优势,求解问题个数明显增多。  相似文献   

3.
The lower bound (LB) implemented in branch and bound MaxSAT solvers is decisive for obtaining a competitive solver. In modern solvers like MaxSatz and MiniMaxSat, the LB relies on the cooperation of the underestimation and inference components. Actually, the underestimation component of some solvers guides the application of the inference component when a conflict is reached and certain structures are found. In this paper we analyze algorithmic and logical aspects of the underestimation components that have been implemented in MaxSatz during its evolution. From an algorithmic point of view, we define novel strategies for selecting unit clauses in UP (the underestimation of LB in UP is the number of independent inconsistent subformulas detected using unit propagation), the extension of UP with failed literal detection, and a clever heuristic for guiding the application of MaxSAT resolution when UP augmented with failed literal detection is applied in the presence of cycles structures. From a logical point of view, we prove that the inconsistent subformulas detected by UP are minimally unsatisfiable, but this property does not hold if failed literal detection is added. In the presence of cycle structures in conflicts detected by UP augmented with failed literal detection, we prove that the application of MaxSAT resolution produces smaller inconsistent subformulas and, besides, generates additional clauses that may be used to improve the LB. The conducted empirical investigation indicates that the LB techniques described in this paper lead to better quality LBs.  相似文献   

4.
For infinitely many n > 0 we construct contradictory formulas αn in conjunctive form with n literals such that every regular proof tree which proves the contradiction must contain 2cn distinct clauses for some c > 0. This implies a 2cn lower bound for the number of distinct clauses which are generated by the Davis-Putnam procedure applied to αn using any order of variable elimination.  相似文献   

5.
Most search techniques within ILP require the evaluation of a large number of inconsistent clauses. However, acceptable clauses typically need to be consistent, and are only found at the “fringe” of the search space. A search approach is presented, based on a novel algorithm called QG (Quick Generalization). QG carries out a random-restart stochastic bottom-up search which efficiently generates a consistent clause on the fringe of the refinement graph search without needing to explore the graph in detail. We use a Genetic Algorithm (GA) to evolve and re-combine clauses generated by QG. In this QG/GA setting, QG is used to seed a population of clauses processed by the GA. Experiments with QG/GA indicate that this approach can be more efficient than standard refinement-graph searches, while generating similar or better solutions. Editors: Ramon Otero, Simon Colton.  相似文献   

6.
W. F. Clocksin 《Software》1985,15(7):669-675
All clauses comprising a Prolog program are stored in a database from which they can be removed later. Other long-term data structures are represented as clauses and are also stored and removed from the same database. Implementation techniques for the manipulation of clauses are not well known, and a lack of information has led to incorrect and incomplete implementations. Further previously unresolved issues are apparent when considering the storage of compiled clauses. We describe the way database manipulations are performed in Prolog-X, a new compiler-based Prolog system. We also introduce a new technique for storing the source form of compiled clauses.  相似文献   

7.
A formal approach is presented for proving temporal properties of dynamic systems. Its main advantage is that it can be used to prove properties of hybrid systems, i.e. those whose state contains both discrete and continuous parameters. In contrast, most current temporal reasoning techniques are restricted either to purely discrete systems or to purely continuous systems. Our approach is based upon a new modeling technique called DMOD. A DMOD model of a system defines the causality relation between events in the system, using definite clauses, i.e. logic programs. Thereby, the problem of reasoning about hybrid systems is reduced to one of reasoning about the behavior of definite clauses. As these possess a simple proof theory, reasoning is substantially simplified.  相似文献   

8.
复句关系类别的识别是对复句分句之间语义关系的甄别,是分析复句语义关系的关键。在现代汉语复句中,二句式和三句式复句占绝大多数,而三句式复句又可以拆分为二句式复句,所以多句式复句的研究归结起来就是二句式复句的研究。因此,本文以二句式非充盈态有标复句为研究对象,结合汉语复句的句法理论、关系标记搭配理论,以汉语复句语料库以及搜索引擎获取的复句为语料,进行二句式非充盈态有标复句关系类别的自动标识。使用本文提出的方法对二句式非充盈态有标复句关系类别进行自动识别,准确率达89%,实验结果证明了本文方法的有效性。  相似文献   

9.
This paper addresses two problems concerning the issue of redundant information in resolution based reasoning systems. The first one deals with the question how the derivation of redundant clauses, such as duplicates or instances of already retained clauses, can be substantially reduced. The second one asks for a criterion to decide, which clauses need not be tested for redundancy. We consider a particular kind of redundancy, which we call ancestor subsumption, that is the subsumption of a resolvent by one of its ancestors. It will be shown that the occurrence of cyclic clause sets, which roughly correspond to sets of logical equivalences, accounts for ancestor subsumed resolvents. Moreover, two techniques will be given to cope with the problems caused by such cyclic structures. The first technique, called literal demodulation, uses logical equivalences as rewrite rules, the second one employs a particular kind of theory resolution.  相似文献   

10.
The paper identifies several new properties of the lattice induced by the subsumption relation over first-order clauses and derives implications of these for learnability. In particular, it is shown that the length of subsumption chains of function free clauses with bounded size can be exponential in the size. This suggests that simple algorithmic approaches that rely on repeating minimal subsumption-based refinements may require a long time to converge. It is also shown that with bounded size clauses the subsumption lattice has a large branching factor. This is used to show that the class of first-order length-bounded monotone clauses is not properly learnable from membership queries alone. Finally, the paper studies pairing, a generalization operation that takes two clauses and returns a number of possible generalizations. It is shown that there are clauses with an exponential number of pairing results which are not related to each other by subsumption. This is used to show that recent pairing-based algorithms can make exponentially many queries on some learning problems.  相似文献   

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