Encouraging Experimental Results on Learning CNF

This paper presents results comparing three simple inductive learning systems using different representations for concepts, namely: CNF formulae, DNF formulae, and decision trees. The CNF learner performs surprisingly well. Results on five natural data sets indicates that it frequently trains faster and produces more accurate and simpler concepts.     

Generalizations of matched CNF formulas

A CNF formula is called matched if its associated bipartite graph (whose vertices are clauses and variables) has a matching that covers all clauses. Matched CNF formulas are satisfiable and can be recognized efficiently by matching algorithms. We generalize this concept and cover clauses by collections of bicliques (complete bipartite graphs). It turns out that such generalization indeed gives rise to larger classes of satisfiable CNF formulas which we term biclique satisfiable. We show, however, that the recognition of biclique satisfiable CNF formulas is NP-complete, and remains NP-hard if the size of bicliques is bounded. A satisfiable CNF formula is called var-satisfiable if it remains satisfiable under arbitrary replacement of literals by their complements. Var-satisfiable CNF formulas can be viewed as the best possible generalization of matched CNF formulas as every matched CNF formula and every biclique satisfiable CNF formula is var-satisfiable. We show that recognition of var-satisfiable CNF formulas is ₂ ^P-complete, answering a question posed by Kleine Büning and Zhao.     

MOS器件二次击穿行为的电路级宏模块建模

采用一种利用TCAD仿真提取MOS器件在静电放电现象瞬间大电流情况下的电学参数,对MOS器件二次击穿行为进行电路级宏模块建模.MOS器件是一种重要的静电放电防护器件,被广泛地应用为集成电路输入输出口的静电保护器件.用TCAD仿真工具对MOS器件的二次击穿进行宏模块建模,该模型能够正确反映MOS器件二次击穿的深刻机理,具有良好的精确性和收敛性,这对在电路级以及系统级层面上仿真静电放电防护网络的抗静电冲击能力有重要意义.     

Generalizations of matched CNF formulas

A CNF formula is called matched if its associated bipartite graph (whose vertices are clauses and variables) has a matching that covers all clauses. Matched CNF formulas are satisfiable and can be recognized efficiently by matching algorithms. We generalize this concept and cover clauses by collections of bicliques (complete bipartite graphs). It turns out that such generalization indeed gives rise to larger classes of satisfiable CNF formulas which we term biclique satisfiable. We show, however, that the recognition of biclique satisfiable CNF formulas is NP-complete, and remains NP-hard if the size of bicliques is bounded. A satisfiable CNF formula is called var-satisfiable if it remains satisfiable under arbitrary replacement of literals by their complements. Var-satisfiable CNF formulas can be viewed as the best possible generalization of matched CNF formulas as every matched CNF formula and every biclique satisfiable CNF formula is var-satisfiable. We show that recognition of var-satisfiable CNF formulas is _P ² P-complete, answering a question posed by Kleine Büning and Zhao.     

用于电路级仿真软故障注入的自动化方法

为了克服电路级仿真故障注入评估软错误敏感性时烦琐费时的缺陷,提出一种将注入过程自动化的方法.使用LL(k)语法分析技术自动解析Spice网表,以自动提取故障注入目标的信息;由程序将网表自动展平,克服了多次例化的子电路无法注入单故障的问题;通过对展平后网表的遍历而自动插入表征软错误的电流源;开发了一个电路级软错误注入器HSECT-SPI,并针对ISCAS'85和ISCAS'89 Benchmark电路进行了故障注入实验,结果表明:文中方法适于自动分析单元和模块电路的软错误敏感性,并可指导高可靠集成电路的设计.     

Redundancy in logic I: CNF propositional formulae

A knowledge base is redundant if it contains parts that can be inferred from the rest of it. We study some problems related to the redundancy of a CNF formula. In particular, any CNF formula can be made irredundant by deleting some of its clauses: what results is an irredundant equivalent subset. We study the complexity of problems related to irredundant equivalent subsets: verification, checking existence of an irredundant equivalent subset with a given size, checking necessary and possible presence of clauses in irredundant equivalent subsets, and uniqueness. We also consider the problem of redundancy with different definitions of equivalence.     

Hardness results for approximate pure Horn CNF formulae minimization

We study the hardness of approximation of clause minimum and literal minimum representations of pure Horn functions in n Boolean variables. We show that unless P=NP, it is not possible to approximate in polynomial time the minimum number of clauses and the minimum number of literals of pure Horn CNF representations to within a factor of \(2^{\log^{1-o(1)} n}\) . This is the case even when the inputs are restricted to pure Horn 3-CNFs with O(n ^1+ε ) clauses, for some small positive constant ε. Furthermore, we show that even allowing sub-exponential time computation, it is still not possible to obtain constant factor approximations for such problems unless the Exponential Time Hypothesis turns out to be false.     

Simulating spin models on GPU

Over the last couple of years it has been realized that the vast computational power of graphics processing units (GPUs) could be harvested for purposes other than the video game industry. This power, which at least nominally exceeds that of current CPUs by large factors, results from the relative simplicity of the GPU architectures as compared to CPUs, combined with a large number of parallel processing units on a single chip. To benefit from this setup for general computing purposes, the problems at hand need to be prepared in a way to profit from the inherent parallelism and hierarchical structure of memory accesses. In this contribution I discuss the performance potential for simulating spin models, such as the Ising model, on GPU as compared to conventional simulations on CPU.     

P2P协议通用仿真器模型设计

P2P技术是一种分布式控制网络技术,它将逐渐取代集中式的客户/服务器结构。P2P的发展非常迅速,目前研究P2P技术流行使用的仿真器存在可仿真协议种类少等问题。文章通过分析P2P各种协议系统及其特性,在分析的基础上设计P2P的通用仿真器模型。     

Redundancy in logic II: 2CNF and Horn propositional formulae

We report results about the redundancy of formulae in 2CNF form. In particular, we give a slight improvement over the trivial redundancy algorithm and give some complexity results about some problems related to finding Irredundant Equivalent Subsets (i.e.s.) of 2CNF formulae. The problems of checking whether a 2CNF formula has a unique i.e.s. and checking whether a clause in is all its i.e.s.'s are polynomial. Checking whether a 2CNF formula has an i.e.s. of a given size and checking whether a clause is in some i.e.s.'s of a 2CNF formula are polynomial or NP-complete depending on whether the formula is cyclic. Some results about Horn formulae are also reported.     

在ARM上模拟串行数据通信方法的研究

系统分析软件模拟串行通信的优缺点,提出一种在ARM上实现软件模拟串行总线接口的通用方法,并成功应用于某ATCA项目中.该方法根据外围器件提供的时序图,利用ARM处理器的IO资源来实现与串行接口芯片的数据通信.     

Simulating fermions on a quantum computer

The real-time probabilistic simulation of quantum systems in classical computers is known to be limited by the so-called dynamical sign problem, a problem leading to exponential complexity. In 1981 Richard Feynman raised some provocative questions in connection to the “exact imitation” of such systems using a special device named a “quantum computer”. Feynman hesitated about the possibility of imitating fermion systems using such a device. Here we address some of his concerns and, in particular, investigate the simulation of fermionic systems. We show how quantum computers avoid the sign problem in some cases by reducing the complexity from exponential to polynomial. Our demonstration is based upon the use of isomorphisms of algebras. We present specific quantum algorithms that illustrate the main points of our algebraic approach.     

微电网的建模仿真研究

研究微电网的建模仿真问题,针对微电网中的微电源种类多样且输出特性各异,由传统的简易微电源模型所构成的微电网平台很难对现今微电网的研究进行仿真.针对以上情况,构建了结构、功能完整的风电机组、燃料电池、带有MPPT(最大功率点跟踪)光伏电池以及柴油发电机等微电源模型,及具有调频作用的二次负载模型,仿真验证了所建模型的合理性及有效性.在此基础上,又构建了一个含多种能源负荷的微型电网模型,对负荷突变及严重故障的条件下微电网维持电能质量和快速恢复的能力予以评估,结果表明所构建的微电源模型和微电网模型能较好地仿真实际情况,为微电网的进一步研究提供了良好的仿真平台.     

虚拟大气环境模拟仿真的研究

为更好地实现视景仿真的实时场景渲染,使虚拟环境更加逼真形象,提出了云彩和薄雾的实现方法,给出了虚拟大气环境的模拟仿真过程.Vega是一个先进的虚拟场景开发工具,采用Vega开发虚拟大气场景,在大气模拟仿真领域有着非常广泛的应用前景.     

CNF and DNF Considered Harmful for Computing Prime Implicants/Implicates

Several methods to compute the prime implicants and the prime implicates of a negation normal form (NNF) formula are developed and implemented. An algorithm PI is introduced that is an extension to negation normal form of an algorithm given by Jackson and Pais. A correctness proof of the PI algorithm is given. The PI algorithm alone is sufficient in a computational sense. However, it can be combined with path dissolution, and it is shown empirically that this is often an advantage. None of these variations rely on conjunctive normal form or on disjunctive normal form. A class of formulas is described for which reliance on CNF or on DNF results in an exponential increase in the time required to compute prime implicants/implicates. The possibility of avoiding this problem with efficient structure preserving clause form translations is examined briefly and appears unfavorable.     

Testing satisfiability of CNF formulas by computing a stable set of points

We show that a conjunctive normal form (CNF) formula F is unsatisfiable if and only if there is a set of points of the Boolean space that is stable with respect to F. So testing the satisfiability of a CNF formula reduces to looking for a stable set of points (SSP). We give some properties of SSPs and describe a simple algorithm for constructing an SSP for a CNF formula. Building an SSP can be viewed as a natural way of search space traversal. This naturalness of search space examination allows one to make use of the regularity of CNF formulas to be checked for satisfiability. We illustrate this point by showing that if a CNF F formula is symmetric with respect to a group of permutations, it is very easy to make use of this symmetry when constructing an SSP. As an example, we show that the unsatisfiability of pigeon-hole CNF formulas can be proven by examining only a set of points whose size is quadratic in the number of holes. Finally, we introduce the notion of an SSP with excluded directions and sketch a procedure of satisfiability testing based on the construction of such SSPs.