Special Research Centre for the Subatomic Structure of Matter publications

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Browsing Special Research Centre for the Subatomic Structure of Matter publications by Author "Adams, D."

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    Accelerated overlap fermions
    (American Physical Soc, 2002) Kamleh, W.; Adams, D.; Leinweber, D.; Williams, A.; Special Research Centre for the Subatomic Structure of Matter
    Numerical evaluation of the overlap Dirac operator is difficult since it contains the sign function ε(Hw) of the Hermitian Wilson-Dirac operator Hw with a negative mass term. The problems are due to Hw having very small eigenvalues on the equilibrium background configurations generated in current day Monte Carlo simulations. Since these are a consequence of the lattice discretization and do not occur in the continuum version of the operator, we investigate in this paper to what extent the numerical evaluation of the overlap can be accelerated by making the Wilson-Dirac operator more continuum-like. Specifically, we study the effect of including the clover term in the Wilson-Dirac operator and smearing the link variables in the irrelevant terms. In doing so, we have obtained a factor of 2 speedup by moving from the Wilson action to a fat link irrelevant clover action as the overlap kernel.
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    Improving the low-lying spectrum of the overlap kernel
    (Elsevier Science BV, 2002) Kamleh, W.; Adams, D.; Leinweber, D.; Williams, A.; Special Research Centre for the Subatomic Structure of Matter
    The action of the overlap-Dirac operator on a vector is typically implemented in directly through a multi-shift conjugate gradient solver. The compute-time this takes to evaluate depends upon the condition number $\kappa$ of the matrix that is used as the overlap kernel. We examine the low-lying spectra of various candidate kernels in an effort to optimise $\kappa$, thereby speeding up the overlap evaluation.