1,137 research outputs found
A hybrid MPI-OpenMP scheme for scalable parallel pseudospectral computations for fluid turbulence
A hybrid scheme that utilizes MPI for distributed memory parallelism and
OpenMP for shared memory parallelism is presented. The work is motivated by the
desire to achieve exceptionally high Reynolds numbers in pseudospectral
computations of fluid turbulence on emerging petascale, high core-count,
massively parallel processing systems. The hybrid implementation derives from
and augments a well-tested scalable MPI-parallelized pseudospectral code. The
hybrid paradigm leads to a new picture for the domain decomposition of the
pseudospectral grids, which is helpful in understanding, among other things,
the 3D transpose of the global data that is necessary for the parallel fast
Fourier transforms that are the central component of the numerical
discretizations. Details of the hybrid implementation are provided, and
performance tests illustrate the utility of the method. It is shown that the
hybrid scheme achieves near ideal scalability up to ~20000 compute cores with a
maximum mean efficiency of 83%. Data are presented that demonstrate how to
choose the optimal number of MPI processes and OpenMP threads in order to
optimize code performance on two different platforms.Comment: Submitted to Parallel Computin
Simulating Film Grain using the Noise Power Spectrum
Adding grain to simulated images makes them look more exciting. While its relativly easy to add some noise, here we use the principles developed by imaging scientists to produce grain which is theoretically "correct". While the results are usefull, they also illustrate the limitations of current photographic theories of grain
Fast Computation of Voigt Functions via Fourier Transforms
This work presents a method of computing Voigt functions and their
derivatives, to high accuracy, on a uniform grid. It is based on an adaptation
of Fourier-transform based convolution. The relative error of the result
decreases as the fourth power of the computational effort. Because of its use
of highly vectorizable operations for its core, it can be implemented very
efficiently in scripting language environments which provide fast vector
libraries. The availability of the derivatives makes it suitable as a function
generator for non-linear fitting procedures.Comment: 8 pages, 1 figur
The numerical simulation tool for the MAORY multiconjugate adaptive optics system
The Multiconjugate Adaptive Optics RelaY (MAORY) is and Adaptive Optics
module to be mounted on the ESO European-Extremely Large Telescope (E-ELT). It
is a hybrid Natural and Laser Guide System that will perform the correction of
the atmospheric turbulence volume above the telescope feeding the Multi-AO
Imaging Camera for Deep Observations Near Infrared spectro-imager (MICADO). We
developed an end-to-end Monte- Carlo adaptive optics simulation tool to
investigate the performance of a the MAORY and the calibration, acquisition,
operation strategies. MAORY will implement Multiconjugate Adaptive Optics
combining Laser Guide Stars (LGS) and Natural Guide Stars (NGS) measurements.
The simulation tool implements the various aspect of the MAORY in an end to end
fashion. The code has been developed using IDL and uses libraries in C++ and
CUDA for efficiency improvements. Here we recall the code architecture, we
describe the modeled instrument components and the control strategies
implemented in the code.Comment: 6 pages, 1 figure, Proceeding 9909 310 of the conference SPIE
Astronomical Telescopes + Instrumentation 2016, 26 June 1 July 2016
Edinburgh, Scotland, U
High energy gravitational scattering: a numerical study
The S-matrix in gravitational high energy scattering is computed from the
region of large impact parameters b down to the regime where classical
gravitational collapse is expected to occur. By solving the equation of an
effective action introduced by Amati, Ciafaloni and Veneziano we find that the
perturbative expansion around the leading eikonal result diverges at a critical
value signalling the onset of a new regime. We then discuss the main features
of our explicitly unitary S-matrix down to the Schwarzschild's radius R=2G
s^(1/2), where it diverges at a critical value b ~ 2.22 R of the impact
parameter. The nature of the singularity is studied with particular attention
to the scaling behaviour of various observables at the transition. The
numerical approach is validated by reproducing the known exact solution in the
axially symmetric case to high accuracy.Comment: 11 pages, 6 figure
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