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gravitySimulator Beyond the Million Body Problem

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  1. gravitySimulatorBeyond the Million Body Problem Stefan Harfst and David Merritt Rochester Institute of Technology Collaborators: Rainer Spurzem (Heidelberg) Peter Berczik (Heidelberg/Kiev) Simon Portegies Zwart (Amsterdam) Alessia Gualandris (Amsterdam) Hans-Peter Bischof (RIT)

  2. Modelling Dense Stellar Systems • one approach: direct N-body simulations • exact but very compute-intensive ~O(N2) • many problems require large N • e.g. the evolution of binary Black holes • “empty losscone” is artificially repopulated by two-body scattering unless N > 106

  3. How to deal with large N • A standard Supercomputer • Special-purpose hardware • GRAvity PipEline (GRAPE) • Customed-designed pipelines for force calculations • Very fast (~1 TFlops) • Limited particle numbers (< 1/4 million) • Cost: ~$50K + extras (GRAPE-6) (J. Makino, T. Fukushige)

  4. mini-GRAPEs (GRAPE-6A) The GRAPE cluster N < 131,072

  5. GRAPE cluster RIT’s gravitySimulator is operational since Feb 2005 • 32 dual 3GHz-Xeon nodes • 32 GRAPE-6A’s • 14 Tbyte RAID • low-latency Infiniband interconnects (10Gbps) • Speed: 4 TFlops • N up to 4 Million particles • Cost: $0.5x106 • Funding: NSF/NASA/RIT • Next largest: • 24 nodes (University of Tokyo) • soon 32 nodes (Heidelberg)

  6. store local particles • select active particles • collect all active particles • compute local force and sum over all nodes GRAPE PC The Code and Performance • new parallel direct-summation code • fourth-order Hermite integrator • individual, block time steps • achieves best performance • for small particle numbers communication dominates • efficiencies are between 60% (many processors) and 90% (few processors) For details see poster

  7. Visualization of N-Body Simulations in collaboration with Hans-Peter Bischof (RIT) • new software package “Spiegel” • GUI to plot N-body data and make movies • See Poster for details