On exact selection of minimally unsatisfiable subformulae

A minimally unsatisfiable subformula (MUS) is a subset of clauses of a given CNF formula which is unsatisfiable but becomes satisfiable as soon as any of its clauses is removed. The selection of a MUS is of great relevance in many practical applications. This expecially holds when the propositional formula encoding the application is required to have a well-defined satisfiability property (either to be satisfiable or to be unsatisfiable). While selection of a MUS is a hard problem in general, we show classes of formulae where this problem can be solved efficiently. This is done by using a variant of Farkas lemma and solving a linear programming problem. Successful results on real-world contradiction detection problems are presented.     

电压无功功率优化控制中不可行问题的研究

分析了电力系统电压无功实时优化控制中出现的不可行问题,通过引入模糊约束,从一个新的角度对不可行问题进行了处理,最终获得尽量靠近原不等式约束空间的解。中结合原对偶内点法的特点提出了不可行问题的探测和中结合原对偶内点法的特点提出了不可行问题的探测和处理方法,并用模型系统和华东电力系统的实际数据进行了验算。结果表明,中所提的方法可以有效地探测和处理优化过程中的不可行问题,快速获得合理解。     

PFC中约束优先级及可行性问题的混杂处理

针对预测函数控制的约束不可行和优先级问题,基于混杂系统以及混合逻辑动态模型的思想提出了约束不可行及优先级问题的混杂PFC处理方法,讨论了由PFC、混杂系统、松弛变量法所组成的约束不可行及优先级问题的具体实现方法与步骤.在通常PFC跟踪性能指标的基础上结合MLD与松弛变量法,通过将命题逻辑转化为混合逻辑不等式并与系统自身...     

A Framework for Optimal Correction of Inconsistent Linear Constraints

The problem of inconsistency between constraints often arises in practice as the result, among others, of the complexity of real models or due to unrealistic requirements and preferences. To overcome such inconsistency two major actions may be taken: removal of constraints or changes in the coefficients of the model. This last approach, that can be generically described as model correction is the problem we address in this paper in the context of linear constraints over the reals. The correction of the right hand side alone, which is very close to a fuzzy constraints approach, was one of the first proposals to deal with inconsistency, as it may be mapped into a linear problem. The correction of both the matrix of coefficients and the right hand side introduces non linearity in the constraints. The degree of difficulty in solving the problem of the optimal correction depends on the objective function, whose purpose is to measure the closeness between the original and corrected model. Contrary to other norms, that provide corrections with quite rigid patterns, the optimization of the important Frobenius norm was still an open problem. We have analyzed the problem using the KKT conditions and derived necessary and sufficient conditions which enabled us to unequivocally characterize local optima, in terms of the solution of the Total Least Squares and the set of active constraints. These conditions justify a set of pruning rules, which proved, in preliminary experimental results, quite successful in a tree search procedure for determining the global minimizer.     

On exact selection of minimally unsatisfiable subformulae

A minimally unsatisfiable subformula (MUS) is a subset of clauses of a given CNF formula which is unsatisfiable but becomes satisfiable as soon as any of its clauses is removed. The selection of a MUS is of great relevance in many practical applications. This expecially holds when the propositional formula encoding the application is required to have a well-defined satisfiability property (either to be satisfiable or to be unsatisfiable). While selection of a MUS is a hard problem in general, we show classes of formulae where this problem can be solved efficiently. This is done by using a variant of Farkas' lemma and solving a linear programming problem. Successful results on real-world contradiction detection problems are presented.     

二手童装市场化前景分析

通过对石家庄市区市场进行二手童装经营可行性的市场调查,说明二手童装不能作为成熟的经营品种进入市场,并在这一基础上较全面地分析了导致这一不可行性的原因。     

化工企业立项时应重视不可行性研究

由于化工企业资金密集 ,厂房、设备专用性强 ,要求立项必须十分准确 ,如果立项错误 ,必将造成大量资金浪费。不可行性研究从反方向来论证可行性程度 ,为全面分析项目的可行性奠定基础 ,以判断项目的最后取舍 ,所以不可行性研究不可缺少     

作业车间调度问题解的不可行性检测算法和快速修复算法

为了判别作业车间调度问题的解的可行性,提出了一种基于图论的启发式判别算法,并通过实例验证了方法的正确性.提出了普适于作业车间调度问题的快速修补新算法,可以对于作业车间调度问题的不可行解进行修正使之变成可行解.判别算法和修补算法在最不利情形下的计算复杂性均为O(n),判别算法在最有利情形下的计算复杂性为O(2 |J|+|M|).所提出的算法具有很大的灵活性,对于局部蚂蚁算法、遗传算法以及一般的作业车间调度问题均适用.     

基于约束主导混合粒子群算法的风力机叶片优化方法研究

为提高叶片在额定风况和低速风况下的功率系数,研究叶片各叶素处的气动外形参数分布。针对风力机通常运行在低风速风况下,而叶片的优化模型很少考虑该因素的影响,建立基于叶素动量理论和Wilson理论的带低风速功率系数的非线性约束优化模型。由于在处理约束条件的惩罚函数法中罚因子难以确定,而导致算法过早陷入局部解的早熟现象,提出一种结合可行性约束主导处理方法的混合粒子群算法。该算法基于粒子群优化和模拟退火理论,采用可行性约束主导在退火概率突跳下对不可行约束解进行随机生存选择,使种群保持多样性,从而朝更优方向进化,解决了非线性约束条件难以处理和种群易陷入局部解的问题。以1.5 MW风力机叶片为研究对象,建立非线性约束优化模型,对该算法进行了验证。研究成果表明该方法可以有效地处理优化模型的非线性约束,避免优化过程陷入早熟,提高了叶片在额定风速和低风速区域的功率系数。为非线性约束处理方法的研究提供了一种很好的理论分析途径。     

Technology forecasting using DEA in the presence of infeasibility

As a predictive application of data envelopment analysis (DEA), technology forecasting using DEA (TFDEA) measures the rate of frontier shift by which the arrival of future technologies can be estimated. However, it is well known that DEA and therefore TFDEA may suffer from the issue of infeasible super‐efficiency especially under the condition of variable returns to scale. This study develops an extended TFDEA model based on the modified super‐efficiency model proposed in the literature, which has the benefit of yielding radial super‐efficiency scores equivalent to those obtained from the original super‐efficiency model when feasibility is present. The previously published application of liquid crystal displays (LCD) is revisited to illustrate the use of the new model. The results show that the proposed approach makes a reasonable forecast for formerly infeasible targets as well as a consistent forecast for feasible targets.