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## Fast Fourier solvers for the tensor product high-order FEM for a Poisson type equation

We present direct logarithmically optimal in theory and fast in practice algorithms to implement the tensor products finite element method (FEM) based on the tensor products of the 1D high-order FEM spaces on multi-dimensional rectangular parallelepipeds for solving the $N$-dimensional Poisson type equation $-\Delta u+\alpha u=f$ ($N\geq 2$) with the Dirichlet boundary conditions. They are based on the well-known Fourier approaches. The key new points are a detailed description for the eigenpairs of the 1D eigenvalue problems for the high order FEM as well as the fast direct and inverse algorithms for expansion in the respective eigenvectors utilizing simultaneously several versions of the FFT (fast Fourier transform). Results of numerical experiments in 2D and 3D cases are presented.

The algorithms can serve for numerous applications, in particular, to implement the tensor product high order finite element methods for various time-dependent partial differential equations (PDEs) including the multidimensional heat, wave and Schrödinger ones.

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This paper deals with the technique known as the periodic synchronous averaging. The exact analytical expression for the fast Fourier transform (FFT) representing the digital spectrum of the signal undergoing periodic synchronous averaging is derived using the general signal and spectral framework. This formula connects the coefficient of Fourier series of the original continuous-time signal with the FFT of the averaged sampled version taking into consideration all the effects such as difference between the true and averaging periods, the attenuation and the leakage. The results of the numerical simulation are presented for the case of periodic signal, which was chosen a train of triangle pulses, the spectrum of which possesses a closed form and whose Fourier series coefficients rapidly decrease with the index. The chosen example allows the authors to illustrate that the waveform of the recovered signal can vary significantly, despite a rather slight difference in values between the true and averaging periods. Another important effect emphasized in the presented paper is that overall distinction between the original and averaged signals measured by means of relative mean square error raises if the total observation length increases while the other parameters remain fixed.

The boundary value problem for the Poisson and Helmholtz equations with a piecewise constant coefficient with a jump on a triangle is studied numerically. At the jump of the coefficient (at the boundary of the media), the docking conditions are set. A compact difference scheme with high accuracy with a relatively small number of calculations is proposed.

Parallel program for the fast Fourier transform is implemented on the basis of MPI (Message Passing Interface) technology. Radix-4 algorithm is chosen as a basic method to use. The dependence of parallel calculation acceleration on the number of processors is studied for two supercomputers. The formula describing the dependence of the calculation time on the number of processors is proposed for the range of the input data volume and supercomputer characteristics. The number of nodes providing you with maximum acceleration of calculation is estimated.

Modern Elbrus-4S and Elbrus-8S processors show floating point performance comparable to the popular Intel processors in the field of high-performance computing. Tasks oriented to take advantage of the VLIW architecture show even greater efficiency on Elbrus processors. In this paper the efficiency of the most popular materials science codes in the field of classical molecular dynamics and quantum-mechanical calculations is considered. A comparative analysis of the performance of these codes on Elbrus processor and other modern processors is carried out

A model for organizing cargo transportation between two node stations connected by a railway line which contains a certain number of intermediate stations is considered. The movement of cargo is in one direction. Such a situation may occur, for example, if one of the node stations is located in a region which produce raw material for manufacturing industry located in another region, and there is another node station. The organization of freight traﬃc is performed by means of a number of technologies. These technologies determine the rules for taking on cargo at the initial node station, the rules of interaction between neighboring stations, as well as the rule of distribution of cargo to the ﬁnal node stations. The process of cargo transportation is followed by the set rule of control. For such a model, one must determine possible modes of cargo transportation and describe their properties. This model is described by a ﬁnite-dimensional system of diﬀerential equations with nonlocal linear restrictions. The class of the solution satisfying nonlocal linear restrictions is extremely narrow. It results in the need for the “correct” extension of solutions of a system of diﬀerential equations to a class of quasi-solutions having the distinctive feature of gaps in a countable number of points. It was possible numerically using the Runge–Kutta method of the fourth order to build these quasi-solutions and determine their rate of growth. Let us note that in the technical plan the main complexity consisted in obtaining quasi-solutions satisfying the nonlocal linear restrictions. Furthermore, we investigated the dependence of quasi-solutions and, in particular, sizes of gaps (jumps) of solutions on a number of parameters of the model characterizing a rule of control, technologies for transportation of cargo and intensity of giving of cargo on a node station.

This proceedings publication is a compilation of selected contributions from the “Third International Conference on the Dynamics of Information Systems” which took place at the University of Florida, Gainesville, February 16–18, 2011. The purpose of this conference was to bring together scientists and engineers from industry, government, and academia in order to exchange new discoveries and results in a broad range of topics relevant to the theory and practice of dynamics of information systems. Dynamics of Information Systems: Mathematical Foundation presents state-of-the art research and is intended for graduate students and researchers interested in some of the most recent discoveries in information theory and dynamical systems. Scientists in other disciplines may also benefit from the applications of new developments to their own area of study.