ОЦЕНКА ПАРАМЕТРОВ РАСПРЕДЕЛЕНИЯ ЛОГАРИФМА СЛОЖНОСТИ ЗАДАЧИ КОММИВОЯЖЕРА
The complexity of the individual traveling salesman problem was analyzed by means of mathematical statistics. The complexity is defined as a number of nodes of the decision tree created by the branch and bound algorithm. We obtained approximate representations for parameters of probability distribution of the natural logarithm of the complexity. These representations are functions of the dimension of the problem. The linear function is used to construct the upper estimation for the quantiles of the natural logarithm of the complexity, in cases when the level of the quantile is more than 0.5. We also applied this formula for the lower bound of the quantiles of levels less than 0.5. Then we used the normal distribution with the parameters and as an approximation of the distribution of the natural logarithm of the complexity. We combined a nonlinear function for the parameter and linear function for and obtained a lower bound for the quantiles of the level 0.95 of the natural logarithm of the complexity. The quality of the estimations was analyzed by the experiment. In our experiment the sample’s quantiles of the level 0.95 differ from the estimation less than 0.3% in the case when the dimension of the problem in range from 45 to 50.
The classical Branch and Bound algorithm for the travelling salesman problem, presented in 1963 by Little J.D.C., Murty K.G., Sweeney D.W., Karel C., is nowadays one of the most popular algorithms to find a minimum Hamiltonian cycle in a complete graph. There are many literature references having an algorithm pseudocode with comments. However, there are some special cases which are not discussed in these references. One of these cases is an-alyzedin this article.
This article is about the probability distribution of the maximum of the logarithm of the complexity of an individual travelling salesman problem. The complexity is defined as a number of nodes of the decision tree, which was created by the branch and bound algorithm. We applied our earlier results that the distribution of the logarithm of the complexity of travelling salesman problem can be approximated by the normal distribution. In combination with the representation of the distribution of maximum of normally distributed random variables, we obtain the approximation for the distribution of the maximum of the complexity in cases of infinitely large samples. The accuracy of the approximation was visualized on the graph. In order to simplify the approximation for comparatively small samples, we used the normal distribution with the parameters equal to the expectation and standard deviation of approximation for infinitely large samples. This allowed us to obtain representations for the normal distribution, which approximates the distribution of the maximum of the natural logarithm of the complexity in series of mm travelling salesman problem of size nn. The quality of the representations was analysed by the experiment. On the graph, we showed the quantiles of the theoretical distribution of the maximum of the logarithm of the complexity and the sample’s quantiles in the case of samples of 500 and 1000 travelling salesman problem.
In this paper we present improvements to one of the most recent and fastest branch-and-bound algorithm for the maximum clique problem—MCS algorithm by Tomita et al. (Proceedings of the 4th international conference on Algorithms and Computation, WALCOM’10, pp. 191–203, 2010). The suggested improvements include: incorporating of an efficient heuristic returning a high-quality initial solution, fast detection of clique vertices in a set of candidates, better initial colouring, and avoiding dynamic memory allocation. Our computational study shows some impressive results, mainly we have solved p_hat1000-3 benchmark instance which is intractable for MCS algorithm and got speedups of 7, 3000, and 13000 times for gen400_p0.9_55, gen400_p0.9_65, and gen400_p0.9_75 instances correspondingly.
Many efficient exact branch and bound maximum clique solvers use approximate coloring to compute an upper bound on the clique number for every subproblem. This technique reasonably promises tight bounds on average, but never tighter than the chromatic number of the graph.
Li and Quan, 2010, AAAI Conference, p. 128–133 describe a way to compute even tighter bounds by reducing each colored subproblem to maximum satisfiability problem (MaxSAT). Moreover they show empirically that the new bounds obtained may be lower than the chromatic number.
Based on this idea this paper shows an efficient way to compute related “infra-chromatic” upper bounds without an explicit MaxSAT encoding. The reported results show some of the best times for a stand-alone computer over a number of instances from standard benchmarks.
A model for organizing cargo transportation between two node stations connected by a railway line which contains a certain number of intermediate stations is considered. The movement of cargo is in one direction. Such a situation may occur, for example, if one of the node stations is located in a region which produce raw material for manufacturing industry located in another region, and there is another node station. The organization of freight traﬃc is performed by means of a number of technologies. These technologies determine the rules for taking on cargo at the initial node station, the rules of interaction between neighboring stations, as well as the rule of distribution of cargo to the ﬁnal node stations. The process of cargo transportation is followed by the set rule of control. For such a model, one must determine possible modes of cargo transportation and describe their properties. This model is described by a ﬁnite-dimensional system of diﬀerential equations with nonlocal linear restrictions. The class of the solution satisfying nonlocal linear restrictions is extremely narrow. It results in the need for the “correct” extension of solutions of a system of diﬀerential equations to a class of quasi-solutions having the distinctive feature of gaps in a countable number of points. It was possible numerically using the Runge–Kutta method of the fourth order to build these quasi-solutions and determine their rate of growth. Let us note that in the technical plan the main complexity consisted in obtaining quasi-solutions satisfying the nonlocal linear restrictions. Furthermore, we investigated the dependence of quasi-solutions and, in particular, sizes of gaps (jumps) of solutions on a number of parameters of the model characterizing a rule of control, technologies for transportation of cargo and intensity of giving of cargo on a node station.
Event logs collected by modern information and technical systems usually contain enough data for automated process models discovery. A variety of algorithms was developed for process models discovery, conformance checking, log to model alignment, comparison of process models, etc., nevertheless a quick analysis of ad-hoc selected parts of a journal still have not get a full-fledged implementation. This paper describes an ROLAP-based method of multidimensional event logs storage for process mining. The result of the analysis of the journal is visualized as directed graph representing the union of all possible event sequences, ranked by their occurrence probability. Our implementation allows the analyst to discover process models for sublogs defined by ad-hoc selection of criteria and value of occurrence probability
Existing approaches suggest that IT strategy should be a reflection of business strategy. However, actually organisations do not often follow business strategy even if it is formally declared. In these conditions, IT strategy can be viewed not as a plan, but as an organisational shared view on the role of information systems. This approach generally reflects only a top-down perspective of IT strategy. So, it can be supplemented by a strategic behaviour pattern (i.e., more or less standard response to a changes that is formed as result of previous experience) to implement bottom-up approach. Two components that can help to establish effective reaction regarding new initiatives in IT are proposed here: model of IT-related decision making, and efficiency measurement metric to estimate maturity of business processes and appropriate IT. Usage of proposed tools is demonstrated in practical cases.