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Research Interests: Algorithms

 

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The calculations discussed on these pages are all computationally expensive. Of course, computers are becoming faster all the time, which means that more complicated calculations will become possible in the future. However, we feel that we can obtain better throughput for our calculations (i.e. tackle larger problems) by harnessing the power of parallel computers. To do this efficiently, new algorithms are needed.

One such algorithm is the DDPHP algorithm. The key idea behind this algorithm is to distribute the entire wave packet twice, so that each processor in the calculation contains two different slices of the wave packet. This means that no communication between the processors is required for all computations. The wave packet only needs to be resynchronized after each iteration. The result is that the percentage of the wave packet that has to be transferred in each iteration decreases with an increasing number of processors. This is in contrast to an algorithm in which the wave packet is only distributed once, because in that case the percentage of the wave packet to be transferred in each iteration actually increases with increasing number of processors. The efficient communication characteristics of the DDPHP algorithm combined with an efficient computational layout means that the algorithm scales linearly with an increasing number of processors. We have used the DDPHP algorithm already in a number of applications in gas-surface scattering.

One disadvantage of the DDPHP method is that it requires a fast interconnect between the processor of the machine, since the amount of data that has to be is still quite significant. Therefore, we are currently working on methods, which are more suited to more loosely connected parallel computers, such as Beowulf clusters. In the long-term we like to connect these methods with the DDPHP method and the Coriolis coupled method we used earlier to obtain a general parallel method that can be used for a variety of systems from large SMP machines with a large number of processors per node to clusters of workstations.

Some recent references

  • Time-dependent wave packet calculations on parallel computers: A new and efficient algorithm for evaluating HΨ
    Anthony J. H. M. Meijer
    Comp. Phys. Commun., 141, 330-341 (2001).
  • Time-dependent reactive scattering calculations using parallel computers
    in ``Time-dependent quantum dynamics''
    S. C. Althorpe, P. Soldan, and G. G. Balint-Kurti (Eds.) (Collaborative Computational Project on Heavy Particle Dynamics (CCP6), Daresbury UK, 2001), 42
    Anthony J. H. M. Meijer.

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