101,458 research outputs found
Accelerating Staggered Fermion Dynamics with the Rational Hybrid Monte Carlo (RHMC) Algorithm
Improved staggered fermion formulations are a popular choice for lattice QCD
calculations. Historically, the algorithm used for such calculations has been
the inexact R algorithm, which has systematic errors that only vanish as the
square of the integration step-size. We describe how the exact Rational Hybrid
Monte Carlo (RHMC) algorithm may be used in this context, and show that for
parameters corresponding to current state-of-the-art computations it leads to a
factor of approximately seven decrease in cost as well as having no step-size
errors.Comment: 4 pages, 2 figures, 1 tabl
The Rational Hybrid Monte Carlo Algorithm
The past few years have seen considerable progress in algorithmic development
for the generation of gauge fields including the effects of dynamical fermions.
The Rational Hybrid Monte Carlo (RHMC) algorithm, where Hybrid Monte Carlo is
performed using a rational approximation in place the usual inverse quark
matrix kernel is one of these developments. This algorithm has been found to be
extremely beneficial in many areas of lattice QCD (chiral fermions, finite
temperature, Wilson fermions etc.). We review the algorithm and some of these
benefits, and we compare against other recent algorithm developements. We
conclude with an update of the Berlin wall plot comparing costs of all popular
fermion formulations.Comment: 15 pages. Proceedings from Lattice 200
A history of the city of Somerville for the first four grades
Thesis (Ed.M.)--Boston Universit
The RHMC algorithm for theories with unknown spectral bounds
The Rational Hybrid Monte Carlo (RHMC) algorithm extends the Hybrid Monte
Carlo algorithm for lattice QCD simulations to situations involving fractional
powers of the determinant of the quadratic Dirac operator. This avoids the
updating increment () dependence of observables which plagues the Hybrid
Molecular-dynamics (HMD) method. The RHMC algorithm uses rational
approximations to fractional powers of the quadratic Dirac operator. Such
approximations are only available when positive upper and lower bounds to the
operator's spectrum are known. We apply the RHMC algorithm to simulations of 2
theories for which a positive lower spectral bound is unknown: lattice QCD with
staggered quarks at finite isospin chemical potential and lattice QCD with
massless staggered quarks and chiral 4-fermion interactions (QCD). A
choice of lower bound is made in each case, and the properties of the RHMC
simulations these define are studied. Justification of our choices of lower
bounds is made by comparing measurements with those from HMD simulations, and
by comparing different choices of lower bounds.Comment: Latex(Revtex 4) 25 pages, 8 postscript figure
The government's child poverty target: how much progress has been made?
Before the 2001 election the Treasury said that `tax and benefit reforms announced in this Parliament will lift over 1.2 million children out of relative poverty'. But official figures released on 11 April show a smaller fall in child poverty, of only 0.5 million since 1996-97. This commentary attempts to explain the discrepancy. Using the data that lie behind the official Households Below Average Income publications, we analyse trend in child poverty, measured against various poverty lines, since 1979. We show how the government's choice of a relative poverty line is making its goal to abolish child poverty more difficult and more expensive. We also discuss how easy the government will find it to make further reductions in child poverty
Exact 2+1 flavour RHMC simulations
We consider the Rational Hybrid Monte Carlo algorithm for performing exact
2+1 flavour fermion simulations. The specific cases of ASQTAD and domain wall
fermions are considered. We find that in both cases the naive performance is
similar to conventional hybrid algorithms.Comment: 3 pages, no figure
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