14,501 research outputs found
A parallel nearly implicit time-stepping scheme
Across-the-space parallelism still remains the most mature, convenient and natural way to parallelize large scale problems. One of the major problems here is that implicit time stepping is often difficult to parallelize due to the structure of the system. Approximate implicit schemes have been suggested to circumvent the problem. These schemes have attractive stability properties and they are also very well parallelizable.\ud
The purpose of this article is to give an overall assessment of the parallelism of the method
Extrapolation-Based Super-Convergent Implicit-Explicit Peer Methods with A-stable Implicit Part
In this paper, we extend the implicit-explicit (IMEX) methods of Peer type
recently developed in [Lang, Hundsdorfer, J. Comp. Phys., 337:203--215, 2017]
to a broader class of two-step methods that allow the construction of
super-convergent IMEX-Peer methods with A-stable implicit part. IMEX schemes
combine the necessary stability of implicit and low computational costs of
explicit methods to efficiently solve systems of ordinary differential
equations with both stiff and non-stiff parts included in the source term. To
construct super-convergent IMEX-Peer methods with favourable stability
properties, we derive necessary and sufficient conditions on the coefficient
matrices and apply an extrapolation approach based on already computed stage
values. Optimised super-convergent IMEX-Peer methods of order s+1 for s=2,3,4
stages are given as result of a search algorithm carefully designed to balance
the size of the stability regions and the extrapolation errors. Numerical
experiments and a comparison to other IMEX-Peer methods are included.Comment: 22 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1610.0051
QTM: computational package using MPI protocol for quantum trajectories method
The Quantum Trajectories Method (QTM) is one of {the} frequently used methods
for studying open quantum systems. { The main idea of this method is {the}
evolution of wave functions which {describe the system (as functions of time).
Then,} so-called quantum jumps are applied at {a} randomly selected point in
time. {The} obtained system state is called as a trajectory. After averaging
many single trajectories{,} we obtain the approximation of the behavior of {a}
quantum system.} {This fact also allows} us to use parallel computation
methods. In the article{,} we discuss the QTM package which is supported by the
MPI technology. Using MPI allowed {utilizing} the parallel computing for
calculating the trajectories and averaging them -- as the effect of these
actions{,} the time {taken by} calculations is shorter. In spite of using the
C++ programming language, the presented solution is easy to utilize and does
not need any advanced programming techniques. At the same time{,} it offers a
higher performance than other packages realizing the QTM. It is especially
important in the case of harder computational tasks{,} and the use of MPI
allows {improving the} performance of particular problems which can be solved
in the field of open quantum systems.Comment: 28 pages, 9 figure
Effective simulation techniques for biological systems
In this paper we give an overview of some very recent work on the stochastic simulation of systems involving chemical reactions. In many biological systems (such as genetic regulation and cellular dynamics) there is a mix between small numbers of key regulatory proteins, and medium and large numbers of molecules. In addition, it is important to be able to follow the trajectories of individual molecules by taking proper account of the randomness inherent in such a system. We describe different types of simulation techniques (including the stochastic simulation algorithm, Poisson Runge-Kutta methods and the Balanced Euler method) for treating simulations in the three different reaction regimes: slow, medium and fast. We then review some recent techniques on the treatment of coupled slow and fast reactions for stochastic chemical kinetics and discuss how novel computing implementations can enhance the performance of these simulations
Group implicit concurrent algorithms in nonlinear structural dynamics
During the 70's and 80's, considerable effort was devoted to developing efficient and reliable time stepping procedures for transient structural analysis. Mathematically, the equations governing this type of problems are generally stiff, i.e., they exhibit a wide spectrum in the linear range. The algorithms best suited to this type of applications are those which accurately integrate the low frequency content of the response without necessitating the resolution of the high frequency modes. This means that the algorithms must be unconditionally stable, which in turn rules out explicit integration. The most exciting possibility in the algorithms development area in recent years has been the advent of parallel computers with multiprocessing capabilities. So, this work is mainly concerned with the development of parallel algorithms in the area of structural dynamics. A primary objective is to devise unconditionally stable and accurate time stepping procedures which lend themselves to an efficient implementation in concurrent machines. Some features of the new computer architecture are summarized. A brief survey of current efforts in the area is presented. A new class of concurrent procedures, or Group Implicit algorithms is introduced and analyzed. The numerical simulation shows that GI algorithms hold considerable promise for application in coarse grain as well as medium grain parallel computers
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