Journal:Informatica
Volume 25, Issue 4 (2014), pp. 581–616
Abstract
Abstract
The paper summarizes the results of research on the modeling and implementation of advanced planning and scheduling (APS) systems done in recent twenty years. It discusses the concept of APS system – how it is thought of today – and highlights the modeling and implementation challenges with which the developers of such systems should cope. Some from these challenges were identified as a result of the study of scientific literature, others – through an in-depth analysis of the experience gained during the development of real-world APS system – a Production Efficiency Navigator (PEN system). The paper contributes to APS systems theory by proposing the concept of an ensemble of collaborating algorithms.
Journal:Informatica
Volume 22, Issue 4 (2011), pp. 489–505
Abstract
In this paper, we consider the so-called structured low rank approximation (SLRA) problem as a problem of optimization on the set of either matrices or vectors. Briefly, SLRA is defined as follows. Given an initial matrix with a certain structure (for example, Hankel), the aim is to find a matrix of specified lower rank that approximates this initial matrix, whilst maintaining the initial structure. We demonstrate that the optimization problem arising is typically very difficult; in particular, the objective function is multiextremal even in simple cases. We also look at different methods of solving the SLRA problem. We show that some traditional methods do not even converge to a locally optimal matrix.
Journal:Informatica
Volume 10, Issue 4 (1999), pp. 457–466
Abstract
The Steiner problem asks for the shortest network that spans a given set of fixed points in the Euclidean plane. The problem is NP hard.
The result of simulation of an idealized “wet” film connecting fixed points is a length-minimizing curve. Increasing the exterior pressure step by step we are able to achieve the film configuration near to the Steiner minimal tree. “Dead-point” situations may occur for some symmetric allocation of fixed points.
The limited simulation experiments show that the average computation time depends almost linearly on the number of fixed points for the situations without “dead-points”.
Journal:Informatica
Volume 5, Issues 3-4 (1994), pp. 364–372
Abstract
We consider finite population slotted ALOHA where each of n terminals has its own transmission probability pi. Given the overall traffic load λ, the probabilities pi are determined in such a way as to maximize throughput. This is achieved by solving a constrained optimization problem. The results of Abramson (1970) are obtained as a special case. Our recent results are improved (Mathar and Žilinskas, 1993).
Journal:Informatica
Volume 1, Issue 1 (1990), pp. 107–124
Abstract
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.