9 research outputs found
Benchmarking MILC code with OpenMP and MPI
A trend in high performance computers that is becoming increasingly popular
is the use of symmetric multiprocessing (SMP) rather than the older paradigm of
MPP. MPI codes that ran and scaled well on MPP machines can often be run on an
SMP machine using the vendor's version of MPI. However, this approach may not
make optimal use of the (expensive) SMP hardware. More significantly, there are
machines like Blue Horizon, an IBM SP with 8-way SMP nodes at the San Diego
Supercomputer Center that can only support 4 MPI processes per node (with the
current switch). On such a machine it is imperative to be able to use OpenMP
parallelism on the node, and MPI between nodes. We describe the challenges of
converting MILC MPI code to using a second level of OpenMP parallelism, and
benchmarks on IBM and Sun computers.Comment: Lattice 2000 (Computers), 5 pages, 3 figure
Scale Determination Using the Static Potential with Two Dynamical Quark Flavors
We study the static potential using gauge configurations that include the
effects of two flavors of dynamical Kogut-Susskind quarks. The configurations,
generated by the MILC collaboration, and used to study the spectrum and
heavy-light decay constants, cover a range . There are
at least four quark masses for each coupling studied. Determination of
from the potential can be used to set a scale. This alternative scale is useful
to study systematic errors on the spectrum and decay constants.Comment: LATTICE99(spectrum) - 3 pages, 4 figure
Improved Measure of Local Chirality
It is popular to probe the structure of the QCD vacuum indirectly by studying
individual fermion eigenmodes, because this provides a natural way to filter
out UV fluctuations. The double-peaking in the distribution of the local chiral
orientation parameter (X) has been offered as evidence, by some, in support of
a particular model of the vacuum. Here we caution that the X-distribution
peaking varies significantly with various versions of the definition of X.
Furthermore, each distribution varies little from that resulting from a random
reshuffling of the left-handed (and independently the right-handed) fields,
which destroys any QCD-induced left-right correlation; that is, the
double-peaking is mostly a phase-space effect. We propose a new universal
definition of the X parameter whose distribution is uniform for randomly
reshuffled fields. Any deviations from uniformity for actual data can then be
directly attributable to QCD-induced dynamics. We find that the familiar double
peak disappears.Comment: Lattice 2004(topology), Fermilab, June 21-26, 2004; 3 pages, 4
figure
Locality and scaling of quenched overlap fermions
The overlap fermion offers the tremendous advantage of exact chiral symmetry
on the lattice, but is numerically intensive. This can be made affordable while
still providing large lattice volumes, by using coarse lattice spacing, given
that good scaling and localization properties are established. Here, using
overlap fermions on quenched Iwasaki gauge configurations, we demonstrate
directly that the overlap Dirac operator's range is comfortably small in
lattice units for each of the lattice spacings 0.20 fm, 0.17 fm, and 0.13 fm
(and scales to zero in physical units in the continuum limit). In particular,
our direct results contradict recent speculation that an inverse lattice
spacing of is too low to have satisfactory localization.
Furthermore, hadronic masses (available on the two coarser lattices) scale very
well.Comment: Lattice 2005 (chiral fermions), 6 pages, 4 figure