Astronomy and Astrophysics – Astronomy
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004dda....35.0407m&link_type=abstract
American Astronomical Society, DDA meeting #35, #04.07; Bulletin of the American Astronomical Society, Vol. 36, p.854
Astronomy and Astrophysics
Astronomy
Scientific paper
The Gradient Particle Magnetohydrodynamics (GPM) algorithm combines the strengths of an adaptive grid code (AMR) and a smoothed particle code (SPH) by instilling grid-quality gradients into a Lagrangian particle code. It is of particular utility for disk/jet systems.
The hypergradient code uses high-precision tuned finite differences to achieve spectral-quality resolution with 5 times the speed of a spectral code. The finite differencing is not based on a high-order polynomial fit. The polynomial scheme has supurb accuracy for low-wavenumber gradients but fails at high wavenumbers. We instead use a scheme tuned to enhance high-wavenumber accuracy at the expense of low wavenumbers, although the loss of low-wavenumber accuracy is negligibly slight. A tuned gradient is capable of capturing all wavenumbers up to 80 percent of the Nyquist limit with an error of no worse than 1 percent. The fact that gradients are based on finite differences enables diverse geometries to be considered and eliminates the parallel communications bottleneck.
The gravity algorithm is based on the Barnes-Hut tree. It evades the latencies associated with memory accesses, divides, and square roots by grouping bundles of particles together into a simultaneous treewalk and using a polynomial series to approximate the divides and square roots. The algorithm runs 10 times faster than the standard tree codes with no loss of accuracy and it works for individual timesteps.
Blackman Eric
Brandenburg Axel
Chandran Benjamin
Dennis Timothy
Howes Gregory G.
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