57 research outputs found
The Chroma Software System for Lattice QCD
We describe aspects of the Chroma software system for lattice QCD
calculations. Chroma is an open source C++ based software system developed
using the software infrastructure of the US SciDAC initiative. Chroma
interfaces with output from the BAGEL assembly generator for optimised lattice
fermion kernels on some architectures. It can be run on workstations, clusters
and the QCDOC supercomputer.Comment: poster presented at Lattice2004(machines
Parallelizing the QUDA Library for Multi-GPU Calculations in Lattice Quantum Chromodynamics
Graphics Processing Units (GPUs) are having a transformational effect on
numerical lattice quantum chromodynamics (LQCD) calculations of importance in
nuclear and particle physics. The QUDA library provides a package of mixed
precision sparse matrix linear solvers for LQCD applications, supporting single
GPUs based on NVIDIA's Compute Unified Device Architecture (CUDA). This
library, interfaced to the QDP++/Chroma framework for LQCD calculations, is
currently in production use on the "9g" cluster at the Jefferson Laboratory,
enabling unprecedented price/performance for a range of problems in LQCD.
Nevertheless, memory constraints on current GPU devices limit the problem sizes
that can be tackled. In this contribution we describe the parallelization of
the QUDA library onto multiple GPUs using MPI, including strategies for the
overlapping of communication and computation. We report on both weak and strong
scaling for up to 32 GPUs interconnected by InfiniBand, on which we sustain in
excess of 4 Tflops.Comment: 11 pages, 7 figures, to appear in the Proceedings of Supercomputing
2010 (submitted April 12, 2010
Status and Future Perspectives for Lattice Gauge Theory Calculations to the Exascale and Beyond
In this and a set of companion whitepapers, the USQCD Collaboration lays out
a program of science and computing for lattice gauge theory. These whitepapers
describe how calculation using lattice QCD (and other gauge theories) can aid
the interpretation of ongoing and upcoming experiments in particle and nuclear
physics, as well as inspire new ones.Comment: 44 pages. 1 of USQCD whitepapers
Calm Multi-Baryon Operators
Outstanding problems in nuclear physics require input and guidance from
lattice QCD calculations of few baryons systems. However, these calculations
suffer from an exponentially bad signal-to-noise problem which has prevented a
controlled extrapolation to the physical point. The variational method has been
applied very successfully to two-meson systems, allowing for the extraction of
the two-meson states very early in Euclidean time through the use of improved
single hadron operators. The sheer numerical cost of using the same techniques
in two-baryon systems has been prohibitive. We present an alternate strategy
which offers some of the same advantages as the variational method while being
significantly less numerically expensive. We first use the Matrix Prony method
to form an optimal linear combination of single baryon interpolating fields
generated from the same source and different sink interpolators. Very early in
Euclidean time this linear combination is numerically free of excited state
contamination, so we coin it a calm baryon. This calm baryon operator is then
used in the construction of the two-baryon correlation functions.
To test this method, we perform calculations on the WM/JLab iso-clover gauge
configurations at the SU(3) flavor symmetric point with m{\pi} 800 MeV
--- the same configurations we have previously used for the calculation of
two-nucleon correlation functions. We observe the calm baryon removes the
excited state contamination from the two-nucleon correlation function to as
early a time as the single-nucleon is improved, provided non-local (displaced
nucleon) sources are used. For the local two-nucleon correlation function
(where both nucleons are created from the same space-time location) there is
still improvement, but there is significant excited state contamination in the
region the single calm baryon displays no excited state contamination.Comment: 8 pages, 3 figures, proceedings for LATTICE 201
Tuning for Three-flavors of Anisotropic Clover Fermions with Stout-link Smearing
In this work we perform the parameter tuning of three flavors of dynamical
clover quarks on anisotropic lattices. The fermion action uses
three-dimensional spatial stout-link smearing. The gauge anisotropy is
determined in a small box with Schr\"odinger background using Wilson-loop
ratios. The fermion anisotropy is obtained from studying the meson dispersion
relation with antiperiodic boundary conditions in the time direction. The
spatial and temporal clover coefficients are fixed to the tree-level
tadpole-improved values, and we demonstrate that they satisfy the
nonperturbative conditions as determined by the Schr\"odinger functional
method. For the desired lattice spacing fm and renormalized
anisotropy , we find the gauge and fermionic anisotropies can be fixed
to quark mass independent values up through the strange quark mass. This work
lays the foundation needed for further studies of the excited-state hadron
spectrum.Comment: 23 pages, 18 figure
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