4 research outputs found
Computational advances in gravitational microlensing: a comparison of CPU, GPU, and parallel, large data codes
To assess how future progress in gravitational microlensing computation at
high optical depth will rely on both hardware and software solutions, we
compare a direct inverse ray-shooting code implemented on a graphics processing
unit (GPU) with both a widely-used hierarchical tree code on a single-core CPU,
and a recent implementation of a parallel tree code suitable for a CPU-based
cluster supercomputer. We examine the accuracy of the tree codes through
comparison with a direct code over a much wider range of parameter space than
has been feasible before. We demonstrate that all three codes present
comparable accuracy, and choice of approach depends on considerations relating
to the scale and nature of the microlensing problem under investigation. On
current hardware, there is little difference in the processing speed of the
single-core CPU tree code and the GPU direct code, however the recent plateau
in single-core CPU speeds means the existing tree code is no longer able to
take advantage of Moore's law-like increases in processing speed. Instead, we
anticipate a rapid increase in GPU capabilities in the next few years, which is
advantageous to the direct code. We suggest that progress in other areas of
astrophysical computation may benefit from a transition to GPUs through the use
of "brute force" algorithms, rather than attempting to port the current best
solution directly to a GPU language -- for certain classes of problems, the
simple implementation on GPUs may already be no worse than an optimised
single-core CPU version.Comment: 11 pages, 4 figures, accepted for publication in New Astronom
The shell game: a panoramic view of Fornax
We present a panoramic study of the Fornax dwarf spheroidal galaxy, using data obtained as part of the VLT Survey Telescope (VST) ATLAS Survey. The data presented here – a subset of the full survey – uniformly cover a region of 25 deg2 centred on the galaxy, in g, r and i bands. This large area coverage reveals two key differences to previous studies of Fornax. First, data extending beyond the nominal tidal radius of the dwarf highlight the presence of a second distinct red giant branch population. This bluer red giant branch appears to be co-eval with the horizontal branch population. Secondly, a shell structure located approximately 1 ∘ . .∘ 4 from the centre of Fornax is shown to be a mis-identified background overdensity of galaxies. This last result casts further doubt on the hypothesis that Fornax underwent a gas-rich merger in its relatively recent past