Informatica

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.

Teaching of computer programming by electronic mail has been held in Lithuanian schools since 1992. School students of upper grades (8–12) took part in the experiments. The experiments showed that students cope better with first stages of programming (specifying the problem, etc.) than with the last ones (programming, debugging). The analysis of programming products (made by their peers) by students themselves may be expected to be an important component of learning and teaching.

We consider here the optimization problems of simple competitive model. There are two servers providing the some service. Each server fix the price and the rate of service. The rate of service defines the customer losses waiting in line for the service. The customer go to the server with lesser total service cost. The total cost includes the service price plus waiting losses. A customer goes away, if the total cost exceeds some critical level. The flow of customers and the service time both are stochastic. There is no known analytical solution for this model. We get the results by Monte Carlo simulation. We get the analytical solution of the simplyfied model.

The model of the HIV/AIDS infection spread is proposed and investigated. The paper deals with some specific features of the disease spread at the initial stage, i.e., when the infection extent is small enough. We propose a model characterizing any risk group by three differential equations. These equations describe the dynamics of active susceptible, active infected, and passive infected individuals. The evaluation of parameters from demographical and medical data is discussed. The package for the investigation of infection is presented, and possibilities to control the infection are shown. Two general directions of control may be distinguished: the HIV/AIDS blood tests and the publicity and availability of protective means. The investigations showed under what conditions the HIV/AIDS infection may be stopped.

The aggregate approach to the formal description, verification and simulation of computer network protocols is considered in the paper. With this approach, the offered design stages can be performed using a single mathematical scheme. The reachability analysis method and the program proof technique are viewed as methods for correctness analysis. The proposed approach for correctness analysis and model construction was used in creating the protocol analysis system PRANAS.