Communications - Scientific Letters of the University of Zilina, 2003 (vol. 5), issue 4
Articles
Allocation Fragments of the Distributed Database
Karol Matiasko
Communications - Scientific Letters of the University of Zilina 2003, 5(4):5-9 | DOI: 10.26552/com.C.2003.4.5-9 
The paper describes the distribution fragments of the database under a mathematical model with criterial function involving the influence of the Transaction and Concurrency proccesing in Database systems. The model could solve variants for replication of the fragments setting constraints in the model. This approach is prepared for revision of actual distribution using real values of the database (cardinality of tables, referential integrity, important requests etc).
Intelligent Transportation Systems
Petr Cenek
Communications - Scientific Letters of the University of Zilina 2003, 5(4):10-15 | DOI: 10.26552/com.C.2003.4.10-15
Intelligent transportation system (ITS) stands for a transportation system with improved quality of control using an added "intelligence". Improved control can be attained by optimisation methods, by simualtions, interactive methods or artificial intelligence. Anyhow, a suitable model of the system, correct input data, optimisation routines and user-friendly environment for data input and output are typical parts of such a system. Basic parts of a transportation system, transportation processes and their models, optimisation methods and problems of implementation of an ITS are discussed in the paper in more detail.
Bus Scheduling as a Graph Coloring Problem
Stanislav Paluch
Communications - Scientific Letters of the University of Zilina 2003, 5(4):16-20 | DOI: 10.26552/com.C.2003.4.16-20
The fundamental vehicle-scheduling problem (VSP) is usually formulated as a matching problem for which there exists a polynomial algorithm. The formulation of VSP as a graph coloring problem may seem not to be practical since a graph coloring problem is NP-hard and it is not a good idea to solve a polynomial problem using a non polynomial algorithm. However, no polynomial algorithms have been found for generalizations of VSP and hence the graph coloring formulation offers good approximation algorithms for their solution.
SQL Algorithm for Solving Markov Models by Graph Method
Stefan Pesko
Communications - Scientific Letters of the University of Zilina 2003, 5(4):21-23 | DOI: 10.26552/com.C.2003.4.21-23
A simple graph algorithm for finding stabilized probabilities of the finite Markov models implemented in SQL is presented. The algorithm generates systematically all oriented spanning trees of a transition graph. The method is demonstrated on the computation of probabilities in the MMPP2/M/1/K queue.
Vehicle Routing Problem with Stochastic Demands
Vaclav Korenar
Communications - Scientific Letters of the University of Zilina 2003, 5(4):24-26 | DOI: 10.26552/com.C.2003.4.24-26
In the introductory section of this paper there is a view of several types of stochastic vehicle routing problems. In the second section of the paper the vehicle routing problem with stochastic demands is described. The following modifications to the vehicle routing problem are required: Customers demand is a random variable with a known probability distribution. Routes must be designed before the actual demands become known.The presence of nonlinear constraints, caused by random demands, can complicate the solution. Under the specific presumptions it is possible to transfer a nonlinear constraint to a linear form. This transformation enables to use...
An Impact of Improvement-Exchange Heuristics to Quality of Probabilistic TSP Solution
Jaroslav Janacek, Juraj Hurtik
Communications - Scientific Letters of the University of Zilina 2003, 5(4):27-35 | DOI: 10.26552/com.C.2003.4.27-35
This paper deals with a probabilistic travelling salesman problem (PTSP), which differs from a travelling salesman problem (TSP) [6] in the demand for a customer visit. In PTSP is each customer visited with a given probability only. An objective function for PTSP is in general hard to enumerate and it is even harder to estimate an influence of a local change of a PTSP solution on the final value of the objective function of the resulting solution. This hardiness complicates construction of an efficient heuristic for this problem. In this contribution we have focused on research of a relation between type of local change operation and the resulting...
Grid Implementation of Parallel Algorithm for Laplacean Equation Computation by Jacobi Iteration Method
Peter Hanuliak, Peter Varsa
Communications - Scientific Letters of the University of Zilina 2003, 5(4):36-41 | DOI: 10.26552/com.C.2003.4.36-41
The article is devoted to the problem of parallel algorithms and their practical implementations. On the basis of parallel computer analysis in the world the parallel systems are divided into two basic groups - synchronous and asynchronous systems - which are very different from the system point of view. This article describes the development of real parallel algorithms for Jacobi iteration. This individual practical example demonstrates the influence of decomposition strategies for performance evaluation of parallel Jacobi iteration and discusses the ways for their parallel implementations.
Supply Chains in Network Economy
Petr Fiala
Communications - Scientific Letters of the University of Zilina 2003, 5(4):42-46 | DOI: 10.26552/com.C.2003.4.42-46
A supply chain can be shown as a set of units interconnected by material, financial, information and decision flows from initial suppliers to ultimate customers. Supply chain management is more and more affected by network business environment and by information and communication technologies. The paper analyzes a combination of non-cooperative and cooperative decision making of supply chains in network economy.
A Note on using Graphs in Regular Scheduling Problems
Peter Czimmermann
Communications - Scientific Letters of the University of Zilina 2003, 5(4):47-48 | DOI: 10.26552/com.C.2003.4.47-48
This paper deals with regular permutation scheduling on graphs. Peško and Czimmermann introduced this problem (in [3]) and it is generalisation of a matrix permutation problem. The goal is to minimise differences between row sums of a real matrix that represents a schedule, but external conditions don't allow moving matrix elements arbitrarily. The conditions can be represented by permutation obtained from a certain graph.
New Real Environment Simulation Models on Railway Network
Karel Sotek, Hynek Bachraty, Jan Ruzbarsky, Viliam Tavac
Communications - Scientific Letters of the University of Zilina 2003, 5(4):49-54 | DOI: 10.26552/com.C.2003.4.49-54
Transport network simulation models become inseparable part of the innovation processes in transport technology. They approach current operation especially in conjunction with the realization of the information and control systems. References about partial applications were published in various occasions. The authors try to offer integrated up-to-date information about result of their work concerning described area. This name is used for the models whose parameters and data structures encompass terms and parameters adapted from the real system in a considerable amount.
Economic Time Series Forecasting: Box-Jenkins Methodology, Signal Processing and Neural Network Approach
Dusan Marcek, Michaela Acova
Communications - Scientific Letters of the University of Zilina 2003, 5(4):55-58 | DOI: 10.26552/com.C.2003.4.55-58
This paper is devoted to the presentation of methods of economic time series analysis and modelling using the Box-Jenkins methodology, the signal processing approach and the feedforward neural network technique. Some results of our research on time series modelling with emphasis on potential improving forecast accuracy are presented here. The assessment of the particular models has been made using the root mean square error.
VOIP Transmission Quality Increase using Adaptive Play-Out Buffer
Marek Repcik
Communications - Scientific Letters of the University of Zilina 2003, 5(4):59-62 | DOI: 10.26552/com.C.2003.4.59-62
In this paper we consider some quality aspects of VoIP (Voice over Internet Protocol) transmission. We try to increase the voice transmission quality using the adaptive play-out buffer instead of common buffer at the receiver's side. The hypothesis is that the less packet-loss probability increases the transmission quality more that the additional jitter decreases it. The aim of this paper is to formulate the problem.
Novel Adaptive Method of Setting Parameters for Marsik Control Algorithm
Samuel Alexik
Communications - Scientific Letters of the University of Zilina 2003, 5(4):63-65 | DOI: 10.26552/com.C.2003.4.63-65
A novel method of Marsik algorithm improvement is described in the paper. The KappaZ parameter in Marsik algorithm representing a required rate of control error oscillations that influences the quality of control most can be changed adaptively to obtain a better process performance. In the original version of the algorithm a constant value of KappaZ = 0,5 is recommended by the author. Here, a concept how to improve control performance by adaptively changing KappaZ is described. An analysis of the parameter influence is made.
Exponential Model of Token Bucket System
Juraj Smiesko
Communications - Scientific Letters of the University of Zilina 2003, 5(4):66-70 | DOI: 10.26552/com.C.2003.4.66-70
In the presented paper we use the Theory of Markovov Chains for simulation of a simple model of the Token Bucket System (TBS). In the first section we deal with a steady-state analysis of the TBS with Exponential model of On-Off Source of human speech. We develop recurrent formulas for state probabilities of the TBS. In the second section we use real parameters of VoIP and we calculate characteristic of the TBS. In the last section the values of probability of a loosing packet are approximated by more types of regression functions. It is shown that the cubic approximation is the most efficient. Using this function we can directly compute values of...
A Note on "More For Less" Paradox in Relation to Economic Problems
Miroslav Plevny
Communications - Scientific Letters of the University of Zilina 2003, 5(4):71-73 | DOI: 10.26552/com.C.2003.4.71-73
The More for Less Paradox is not only an interesting theoretic construction. An optimization problem, which has this interesting property, can also be found in the real economic world. This contribution was stimulated by the paper [4], which results from the contribution [1] and [2] discussing one interesting property of the linear programming models behaviour, and comments on it and discusses it further. In the paper we attempt to show on a concrete case of a real practical problem [5] that similar property does not need to be a purely theoretical plaything, and it can also be spotted when analysing different variants of a real problem solution.
Deadlock Solving in Transport System with Methods from Computer Operating System
Michal Zarnay
Communications - Scientific Letters of the University of Zilina 2003, 5(4):74-77 | DOI: 10.26552/com.C.2003.4.74-77
In its first part, the article compares control principles in computer operating systems and in transport systems, and outlines similarities. One part of the control in both systems is handling of deadlock situations. When replacing human control by computer control in transport systems, handling of deadlock situations must be tackled as well. In its second part, the article outlines algorithms used in the operating systems field for that and discusses their potential application in the transport systems field. It comes to a conclusion that avoidance of deadlock by dynamic analysis of requested and assigned resources to processes looks to be the most...
Effective Bandwidth for Deterministic Networks
Katarína Bachrata
Communications - Scientific Letters of the University of Zilina 2003, 5(4):78-82 | DOI: 10.26552/com.C.2003.4.78-82
In present paper are given exact definitions of the studied notions. Some elementary properties of an effective bandwidth are deduced. Some terms and results are illustrated with examples for finite as well as for infinite packet flows in the internet network.
To a Performance Evaluation of Parallel Algorithms in Now
Juraj Hanuliak
Communications - Scientific Letters of the University of Zilina 2003, 5(4):83-88 | DOI: 10.26552/com.C.2003.4.83-88
A recent trend in high performance computing (HPC) is to use networks of workstations (NOW) as a cheaper alternative to massively parallel multiprocessors or supercomputers. In such parallel systems (NOW's) individual workstations are connected through widely used communication standard networks and co-operate to solve one large problem. Every workstation is treated similarly as a processing element in a conventional multiprocessor system. To make the whole system appear to the applications as a single parallel computing engine (a virtual parallel system), run-time environments such as PVM (Parallel virtual machine), MPI (Message passing interfaces)...
The Aircraft Landing Problem
Jan Pelikan
Communications - Scientific Letters of the University of Zilina 2003, 5(4):89-91 | DOI: 10.26552/com.C.2003.4.89-91
The problem studied in the paper is an air traffic problem on the airport runway. The goal is finding an aircraft landing sequence that meets the time window for the particular aircraft and at the same time the separation times between two aircraft, which is necessary for the security of landings. The integer programming formulations and the relationship to the traveling salesman problem with cumulative costs are shown.
Design of a Traffic Microsimulation in UML
Genia Ortis
Communications - Scientific Letters of the University of Zilina 2003, 5(4):92-96 | DOI: 10.26552/com.C.2003.4.92-96
From the programming point of view traffic microsimulations consist of concurrent, interacting processes. Several representations of the same type (i.e. a car) are simulated over time. This structure highly corresponds to the concept of object oriented programming, which is therefore the first choice for the implementation of a traffic microsimulation. However, object oriented software has to be designed througly before the first line of program code is writen. Otherwise, with the expansion of the software and the increase of the number of developers a serious danger of incompatibilities and incorrect model behaviour arises. There exists a standard...