Ivan Dimov
Bulgarian Academy of Sciences
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Featured researches published by Ivan Dimov.
Journal of Computational and Applied Mathematics | 1998
Ivan Dimov; Todor V. Gurov
A new approach of iterative Monte Carlo algorithms for the well-known inverse matrix problem is presented and studied. The algorithms are based on a special techniques of iteration parameter choice, which allows to control the convergence of the algorithm for any column (row) of the matrix using different relaxation parameters. The choice of these parameters is controlled by a posteriori criteria for every Monte Carlo iteration. The presented Monte Carlo algorithms are implemented on a SUN Sparkstation. Numerical tests are performed for matrices of moderate in order to show how work the algorithms. The algorithms under consideration are well parallelized.
Environmental Modeling & Assessment | 2001
Zahari Zlatev; Ivan Dimov; Tz. Ostromsky; Gerald Geernaert; Ilia Tzvetanov; Annemarie Bastrup-Birk
In order to help guide air pollution legislation at the European level, harmful air pollution effects on agriculture crops and the consequent economic implications for policy have been studied for more than a decade. Ozone has been labeled as the most serious of the damaging air pollutants to agriculture, where growth rates and consequently yields are dramatically reduced. Quantifying the effects has formed a key factor in policymaking. Based on the widely held view that AOT40 (Accumulated exposure Over Threshold of 40 ppb) is a good indicator of ozone-induced damage, the Danish Eulerian Model (DEM) was used to compute reduced agriculture yields on a 50 km×50 km grid over Europe. In one set of scenarios, a ten year meteorological time series was combined with realistic emission inventories. In another, various idealized emission reduction scenarios are applied to the same meteorological time series. The results show substantial inter-annual variability in economic losses, due in most part to meteorological conditions which varied much more substantially than the emissions during the same period. It is further shown that, taking all uncertainties into account, estimates of ozone-induced economic losses require that a long meteorological record is included in the analysis, for statistical significance to be improved to acceptable levels for use in policy analysis. In this study, calculations were made for Europe as a whole, though this paper presents results relevant for Denmark.
computational science and engineering | 1994
Zahari Zlatev; Ivan Dimov; Krassimir Georgiev
NO ONE DOUBTS THAT HIGH CONCENTRATIONS OF air pollutants can damage (either directly or indirectly) plants, animals, and people. But at what point do these concentrations go from acceptable to dangerous level-nd just as importantly, from dangerous to acceptable? Recent environmental studies show that in order to prevent ecosystem destruction, it is absolutely necessary to reduce the concentration and deposition of certain dangerous air pollutants, at least in Europe and North America, to acceptable levels, and keep them there. These are urgent tasks: some damaging effects may soon be irreversible. O n the other hand, because lowering pollution levels is expensive, we need to reduce them to safe levels but no further. T h e critical concentration of a pollutant is the highest concentration that will not damage biological systems over a long period of time, say 50 years. Deposition is the physical process by which air pollutants are returned to the surface of the Earth. There are two deposition mechanisms: d y deposition takes place continuously, and met depos.itioii occurs only during precipitation periods. Concentration and deposition are two separate processes, with significant but different effects on people and the environment; much of the discussion below deals with both. However, for the sake of brevity in this discussion, we’ll use the term “concentration” to mean both concentration and deposition. T h e two problems outlined-establishing critical concentration levels of pollutants and developing effective control strategies to keep pollutants just under those levels--are very complicated, for a t least three reasons:
Journal of Computational and Applied Mathematics | 1993
Ivan Dimov; Ognyan I. Tonev
Abstract The paper deals with the performance analysis of three Monte Carlo algorithms for some models of computer architectures. To estimate the performance and the speedup of these algorithms, we introduce a special modification of the criterion for the time required to achieve a preset probable error and consider a serial (von Neumann) architecture, a pipeline architecture, and two MIMD (Multiple Instruction stream, Multiple Data stream) parallel architectures. An approach to constructing Monte Carlo vector algorithms to be efficiently run on pipeline computers has also been considered.
Monte Carlo Methods and Applications | 2014
Jean Michel D. Sellier; Mihail Nedjalkov; Ivan Dimov; Siegfried Selberherr
Abstract. The Wigner equation is a promising full quantum model for the simulation of nanodevices. It is also a challenging numerical problem. Two basic Monte Carlo approaches to this model exist exploiting, in the time-dependent case, the so-called particle affinity and, in the stationary case, integer particle signs. In this paper we extend the second approach for time-dependent simulations and present a validation against a well-known benchmark model, the Schrödinger equation. Excellent quantitative agreement is demonstrated by the compared results despite the very different numerical properties of the utilized stochastic and deterministic approaches.
6th International Conference on Finite Difference Methods, FDM 2014 | 2015
Ivan Dimov; István Faragó; Lubin G. Vulkov
This volume is the Proceedings of the First Conference on Finite Difference Methods which was held at the University of Rousse, Bulgaria, 10--13 August 1997. The conference attracted more than 50 participants from 16 countries. 10 invited talks and 26 contributed talks were delivered. The volume contains 28 papers presented at the Conference. The most important and widely used methods for solution of differential equations are the finite difference methods. The purpose of the conference was to bring together scientists working in the area of the finite difference methods, and also people from the applications in physics, chemistry and other natural and engineering sciences.
Mathematics and Computers in Simulation | 2004
Ivan Dimov; István Faragó; Ágnes Havasi; Zahari Zlatev
In this paper the splitting error arising in the Danish Eulerian Model is investigated. Sufficient conditions under which the local splitting error vanishes are formulated for the continuous case. The numerical solution of the model problem introduces several other error sources, which makes the task of determining the effect of the splitting error more complicated. Therefore, we need numerical examples which will allow us to separate the splitting errors from the other errors in order to evaluate both the magnitude of these errors and the relationships between splitting errors and other errors for different values of the discretization parameters. Several such examples have been constructed and analysed. The appropriate conclusions were drawned. The experiences obtained from these experiments can be a starting step towards a total error analysis of the numerical solution of split systems of partial differential equations.
Mathematics and Computers in Simulation | 1998
Ivan Dimov; Vassil N. Alexandrov
An apparatus for raising and supporting the foundation or slab of a building in which a lifting assembly is inserted underneath the foundation or slab and is adapted to receive a pipe assembly. A clamping assembly is provided for engaging a portion of the pipe assembly extending above the lifting assembly, and a hydraulic system extends between the lifting assembly and the clamping assembly for sequentially lowering the pipe assembly into the ground so that, when it encounters resistance, the foundation or slab is supported and can be raised to a predetermined level.
Parallel Algorithms and Applications | 1994
Graham M. Megson; V.N. Aleksandrov; Ivan Dimov
ABSTRACT A systolic array for inverting an n × n matrix using a Monte Carlo method is proposed. The basic array computes a single row of the inverse in 3n + N + T steps ( including input and output time) and O( nNT) cells where N is the number of chains and T is the length of each chain in the stochastic process. A full inverse is computed in the same time but requires O(n2NT) cells. Further improvements reduce the time to 3n/ 2 + N + T using the same number of cells. A number of bounds on N and T are established which show that our design is faster than existing designs for reasonably large values of n Indeed the final arrays require less than n4 cells and have a computing time bounded above by 4n.
Journal of Computational Physics | 2014
Jean Michel D. Sellier; Ivan Dimov
The aim of ab-initio approaches is the simulation of many-body quantum systems from the first principles of quantum mechanics. These methods are traditionally based on the many-body Schrodinger equation which represents an incredible mathematical challenge. In this paper, we introduce the many-body Wigner Monte Carlo method in the context of distinguishable particles and in the absence of spin-dependent effects. Despite these restrictions, the method has several advantages. First of all, the Wigner formalism is intuitive, as it is based on the concept of a quasi-distribution function. Secondly, the Monte Carlo numerical approach allows scalability on parallel machines that is practically unachievable by means of other techniques based on finite difference or finite element methods. Finally, this method allows time-dependent ab-initio simulations of strongly correlated quantum systems. In order to validate our many-body Wigner Monte Carlo method, as a case study we simulate a relatively simple system consisting of two particles in several different situations. We first start from two non-interacting free Gaussian wave packets. We, then, proceed with the inclusion of an external potential barrier, and we conclude by simulating two entangled (i.e. correlated) particles. The results show how, in the case of negligible spin-dependent effects, the many-body Wigner Monte Carlo method provides an efficient and reliable tool to study the time-dependent evolution of quantum systems composed of distinguishable particles.