Informatica - Volume 11, issue 4

Authors: Brosalina, Anna | Melnikov, Boris

Article Type: Research Article

Abstract: This work is an attempt of generalization of the simple statement about the requirements of commutation of words for the case of languages. In the paper, the necessary condition for commutation of languages are obtained, and in the prefix case the necessary and sufficient conditions are obtained. It is important to note that the considered alphabets and languages can be infinite. The possibilities of application of the obtained results are shown in the other problems of the theory of formal languages. The boundary problems for the further solution are formulated.

Keywords: formal languages, commutation of languages, infinite and prefix languages

DOI: 10.3233/INF-2000-11401

Citation: Informatica, vol. 11, no. 4, pp. 353-370, 2000

Authors: Čiegis, Raimondas | Suboč, Olga | Čiegis, Remigijus

Article Type: Research Article

Abstract: The accuracy of adaptive integration algorithms for solving stiff ODE is investigated. The analysis is done by comparing the discrete and exact amplification factors of the equations. It is proved that the usage of stiffness number of the Jacobian matrix is sufficient in order to estimate the complexity of solving ODE problems by explicit integration algorithms. The complexity of implicit integration algorithms depends on the distribution of eigenvalues of the Jacobian. Results of numerical experiments are presented.

Keywords: stiff ODE, adaptive integration, explicit and implicit algorithms

DOI: 10.3233/INF-2000-11402

Citation: Informatica, vol. 11, no. 4, pp. 371-380, 2000

Authors: Dičiūnas, Valdas | Raudys, Šarūnas

Article Type: Research Article

Abstract: An estimation of the generalization performance of classifier is one of most important problems in pattern clasification and neural network training theory. In this paper we estimate the generalization error (mean expected probability of classification) for randomized linear zero empirical error (RLZEE) classifier which was considered by Raudys, Dičiūnas and Basalykas. Instead of “non-explicit” asymptotics of a generalization error of RLZEE classifier for centered multivariate spherically Gaussian classes proposed by Basalykas et al. (1996) we obtain an “explicit” and more simple asymptotics. We also present the numerical simulations illustrating our theoretical results and comparing them with each other and previously …obtained results. Show more

Keywords: randomized linear classifier, generalization error, Gaussian classes, probability of misclassification

DOI: 10.3233/INF-2000-11403

Citation: Informatica, vol. 11, no. 4, pp. 381-396, 2000

Authors: Garliauskas, Algis | Šoliūnas, Alvydas

Article Type: Research Article

Abstract: In this paper, the hexagonal approach was proposed for modeling the functioning of cerebral cortex, especially, the processes of learning and recognition of visual information. This approach is based on the real neurophysiological data of the structure and functions of cerebral cortex. Distinctive characteristic of the proposed neural network is the hexagonal arrangement of excitatory connections between neurons that enable the spreading or cloning of information on the surface of neuronal layer. Cloning of information and modification of the weight of connections between neurons are used as the basic principles for learning and recognition processes. Computer simulation of the hexagonal …neural network indicated a suitability and prospectiveness of proposed approach in the creation, together with other modern concepts, of artificial neural network which will realize the most complicated processes that take place in the brain of living beings, such as short-term and long-term memory, episodic and declarative memory, recall, recognition, categorisation, thinking, and others. Described neural network was realized with computer program written on Delfi 3 language named the first order hexagon brainware (HBW-1). Show more

Keywords: visual cortex, thalamus, pyramidal neuron, hexagonal approach

DOI: 10.3233/INF-2000-11404

Citation: Informatica, vol. 11, no. 4, pp. 397-410, 2000

Authors: Grigolienė, Rasa | Švitra, Donatas

Article Type: Research Article

Abstract: This article is an introduction to the simplest mathematical model, which describes the hormone interaction during the menstrual cycle. Modifications of the mathematical model of the menstrual cycle including the mathematical model with the time delay depending on function researched and the mathematical model with the dispersed time delay are researched and described here. A numerical investigation was conducted, during which solutions for the above mentioned models were calculated. The solutions found are compared mutually and with the clinical data.

Keywords: mathematical modeling, time delay, menstrual cycle

DOI: 10.3233/INF-2000-11405

Citation: Informatica, vol. 11, no. 4, pp. 411-420, 2000

Authors: Ho, James K.

Article Type: Research Article

Abstract: It is well known that in linear programming, the optimal values of the dual variables can be interpreted as shadow prices (marginal values) of the right-hand side coefficients. However, this is true only under nondegeneracy assumptions. Since real problems are often degenerate, the output from conventional LP software regarding such marginal information can be misleading. This paper surveys and generalizes known results in this topic and demonstrates how true shadow prices can be computed with or without modification to existing software.

Keywords: linear programming, shadow prices, optimization software

DOI: 10.3233/INF-2000-11406

Citation: Informatica, vol. 11, no. 4, pp. 421-434, 2000

Authors: Hwang, Min-Shiang

Article Type: Research Article

Abstract: This paper discusses a known-plaintext attack on a redundancy reducing cipher method which is proposed by Wayner. We also propose an extension of Wayner's redundancy reducing cipher scheme so that the security will be improved greatly.

Keywords: cryptography, data encryption standard (DES), Huffman coding

DOI: 10.3233/INF-2000-11407

Citation: Informatica, vol. 11, no. 4, pp. 435-440, 2000

Authors: Melnikov, Boris | Kashlakova, Elena

Article Type: Research Article

Abstract: We consider in this paper so called simple bracketed languages having special limitations. They are sometimes used for the definitions of some grammatical structures of programming languages. Generally speaking, these languages are context-free, but not deterministic context-free, i.e., they cannot be defined by deterministic push-down automata. For the simple bracketed languages having special limitations, the equivalence problem is decidable. We obtain the sufficient conditions for the representation some language by special sequences of simple bracketed languages. We also consider the examples of grammatical structures as the simple bracketed languages. Therefore, we can decide equivalence problem for some grammatical structures …of programming languages, and such structures define neither regular, nor deterministic context-free languages. Show more

Keywords: context-free languages, bracket languages, equivalence problem

DOI: 10.3233/INF-2000-11408

Citation: Informatica, vol. 11, no. 4, pp. 441-454, 2000

Authors: Sakalauskas, Leonidas

Article Type: Research Article

Abstract: Methods for solving stochastic optimization problems by Monte-Carlo simulation are considered. The stoping and accuracy of the solutions is treated in a statistical manner, testing the hypothesis of optimality according to statistical criteria. A rule for adjusting the Monte-Carlo sample size is introduced to ensure the convergence and to find the solution of the stochastic optimization problem from acceptable volume of Monte-Carlo trials. The examples of application of the developed method to importance sampling and the Weber location problem are also considered.

Keywords: Monte-Carlo method, stochastic optimization, statistical decisions

DOI: 10.3233/INF-2000-11409

Citation: Informatica, vol. 11, no. 4, pp. 455-468, 2000

Authors: Šaltenis, Vydūnas

Article Type: Research Article

Abstract: The result of simulation of an idealized thin wet film connecting fixed points in the Euclidean plane is a length-minimizing curve. Gradually increasing the exterior pressure we are able to achieve the film configuration near to the Steiner minimal tree. This film evolution may be an interesting tool for solving the Euclidean Steiner problem, but several dead-point situations may occur for a certain location of fixed points. A continuous evolution of the film is impossible by increasing the pressure in these situations. The investigation of dead-point situations gives the ways of overcoming the difficulties of dead-point situations and continuing the …film evolution by temporarily decreasing pressure. Show more

Keywords: optimization, Steiner problem, wet film, simulation

DOI: 10.3233/INF-2000-11410

Citation: Informatica, vol. 11, no. 4, pp. 469-478, 2000