In this report we describe the conversion of a simple Master-Worker parallel program from global blocking communications to non-blocking communications. The program is MPI-based and has been run on different computer architectures. By moving the communication to the background the processors can use the former waiting time for computation. However we find that the computing time increases by the time the communication time decreases in the used MPICH implementation on a cluster of workstations. Also using non-global communication instead of the global communication slows the algorithm down on computers with optimized global communication routines like the Cray T3D.

Im Rahmen der Arbeit in der damaligen DFG-Forschungsgruppe ¨Scientific Parallel Computing¨ wurde ein hierarchischer paralleler Netzgenerator fuer das Finite-Elemente- Programmpaket SPC-PM CFD unter dem Namen NETGEN69 entwickelt. Als Programmiersprache wurde seinerzeit - wie auch in den FEM-Programmen selbst - FORTRAN benutzt. Im Rahmen des Teilprojektes B2 im Sonderforschungsbereich 393 bestand nunmehr die Aufgabe, den Netzgenerator in ein objektorientiertes Layout zu fassen und in C++zu implementieren. Die Beschreibung von Ein- und Ausgabedaten kann in [3] nachgelesen werden. Die Form der Eingabedaten hat sich aus Kompatibilitaetsgruenden nicht geaendert und wird auch in Zukunft so beibehalten werden. Auch das der Assemblierung und FEM-Rechnung zuge- wandte Interface wurde vorerst nicht geaendert. Ein Wrapper, der fuer die Generierung der erwarteten Ausgabedaten aus den netzgeneratoreigenen Datenbestaenden sorgt, ist derzeit in Planung. Diese Lösung ist freilich nur voruebergehender Natur; sie ermoeglicht es uns, den Netzgenerator innerhalb der FEM-Bibliotheken zu testen.

This paper is devoted to asymptotic estimates for the condition numbers $\kappa(T_n(a))=||T_n(a)|| ||T_n^(-1)(a)||$ of large $n\cross n$ Toeplitz matrices $T_N(a)$ in the case where $\alpha \element L^\infinity$ and $Re \alpha \ge 0$ . We describe several classes of symbols $\alpha$ for which $\kappa(T_n(a))$ increases like $(log n)^\alpha, n^\alpha$ , or even $e^(\alpha n)$ . The consequences of the results for singular values, eigenvalues, and the finite section method are discussed. We also consider Wiener-Hopf integral operators and multidimensional Toeplitz operators.

We describe the structure of those graphs that have largest spectral radius in the class of all connected graphs with a given degree sequence. We show that in such a graph the degree sequence is non-increasing with respect to an ordering of the vertices induced by breadth-first search. For trees the resulting structure is uniquely determined up to isomorphism. We also show that the largest spectral radius in such classes of trees is strictly monotone with respect to majorization. This paper is the revised final version of the preprint no. 35 of this research report series. (author´s abstract) / Series: Research Report Series / Department of Statistics and Mathematics

Given an undirected graph G(V,E) and a vertex subset U\subseteq V the U-space is the vector space over GF(2) spanned by the paths with end-points in U and the cycles in G(V,E). We extend Vismara's algorithm to the computation of the union of all minimum length bases of the U-space. (author's abstract) / Series: Preprint Series / Department of Applied Statistics and Data Processing

We show that results on the characterization of admissible quantizations, which have been derived in Potzelberger [3], have to be modified in case the probability distribution has linear components. Furthermore, we provide an example, where the limit of optimal quantizations is not admissible. (author's abstract) / Series: Forschungsberichte / Institut für Statistik

Let P be a Borel probability measure on Rd. We characterize the maximal elements p E M(P,m) with respect to the Bishop-De Leeuw order, where p E M(P, m) if and only if p P and [supp(p)] m. The results obtained have important consequences for statistical inference, such as tests of homogeneity or multivariate cluster analysis and for the theory of comparison of experiments. (author's abstract) / Series: Forschungsberichte / Institut für Statistik

Location dataflow analysis of mobile objects in GSM network is performed in this project. Dataflow are analyzed in these network nodes: BTS, BSC, MSC, and HLR. During research it is analyzed how data flows changes during day period, how these changes influence network nodes. The possibilities to gather and store data about subscribers' location are explored. The main target of this project is to set guidelines for implementation of European Union directive ST15449 in real GSM networks. Statistic data about data flow types is supplied by real GSM network operator. Experiments were performed using emulator of GSM network data flows. Additional features necessary for analysis were specified and implemented. After analysis it is determined that lowest impact of location dataflow is for BSC component. It is proposed to implement any location data gathering device in BSC nodes.

The one-dimensional distribution of pseudo-random numbers generated by the ratio of uniforms methods using linear congruential generators (LCGs) as the source of uniform random numbers is investigated in this paper. Due to the two-dimensional lattice structure of LCGs there is always a comparable large gap without a point in the one-dimensional distribution of any ratio of uniforms method. Lower bounds for these probabilities only depending on the modulus and the Beyer quotient of the LCG are proved for the case that the Cauchy the normal or the exponential distribution are generated. These bounds justify the recommendation not to use the ratio of uniforms method combined with LCGs. (author's abstract) / Series: Preprint Series / Department of Applied Statistics and Data Processing

To evaluate the expectation of a simple function with respect to a complicated multivariate density Monte Carlo integration has become the main technique. Gibbs sampling and importance sampling are the most popular methods for this task. In this contribution we propose a new simple general purpose importance sampling procedure. In a simulation study we compare the performance of this method with the performance of Gibbs sampling and of importance sampling using a vector of independent variates. It turns out that the new procedure is much better than independent importance sampling; up to dimension five it is also better than Gibbs sampling. The simulation results indicate that for higher dimensions Gibbs sampling is superior. (author's abstract) / Series: Preprint Series / Department of Applied Statistics and Data Processing