Truncated Overlap Fermions

In this talk I propose a new computational scheme with overlap fermions and a fast algorithm to invert the corresponding Dirac operator.Comment: LATTICE99(algorithms

Global Monte Carlo for fermions using ordered statistics

In this talk I discuss a new possibility for stochastic representation of the fe rmion determinant. The method can be used for global Monte Carlo fermion algorit hms and is tested in the case of the Schwinger model.Comment: 3 pages, Lattice2003 (Machines I

Scaling in SU(3) theory with a MCRG improved lattice action

We test various improved gauge actions which are made of linear combinations of Wilson loops. We observe the restoration of rotational symmetry in the static interquark potential already on coarse lattices as small as 6^3x12. Furthermore, we study scaling and asymptotic scaling of the string tension with a MCRG-improved action on 12^3x24 lattices. Preliminary results show that scaling sets in at a ~ 0.3 fm.Comment: 3 pages, 4 figures, contribution at Lattice '97, Edinburg

Exact Local Bosonic Algorithm for Dynamical Quarks

We present an exact local bosonic algorithm for the simulation of dynamical fermions in lattice QCD. We show that this algorithm is a viable alternative to the Hybrid Monte Carlo algorithm.Comment: 3 pages, 1 PostScript figure; Talk presented at LATTICE96(algorithms

Non-hermitian Exact Local Bosonic Algorithm for Dynamical Quarks

We present an exact version of the local bosonic algorithm for the simulation of dynamical quarks in lattice QCD. This version is based on a non-hermitian polynomial approximation of the inverse of the quark matrix. A Metropolis test corrects the systematic errors. Two variants of this test are presented. For both of them, a formal proof is given that this Monte Carlo algorithm converges to the right distribution. Simulation data are presented for different lattice parameters. The dynamics of the algorithm and its scaling in lattice volume and quark mass are investigated.Comment: 32 pages, LaTex, 8 ps figure

Chiral Fermions and Multigrid

Lattice regularization of chiral fermions is an important development of the theory of elementary particles. Nontheless, brute force computer simulations are very expensive, if not prohibitive. In this letter I exploit the non-interacting character of the lattice theory in the flavor space and propose a multigrid approach for the simulation of the theory. Already a two-grid algorithm saves an order of magnitude of computer time for fermion propagator calculations.Comment: Latex, 6 pages, 1 figur

The overlap operator as a continued fraction

We use a continued fraction expansion of the sign-function in order to obtain a five dimensional formulation of the overlap lattice Dirac operator. Within this formulation the inverse of the overlap operator can be calculated by a single Krylov space method where nested conjugate gradient procedures are avoided. We show that the five dimensional linear system can be made well conditioned using equivalence transformations on the continued fractions. This is of significant importance when dynamical overlap fermions are simulated.Comment: 3 pages, 1 figure, talk presented by U. Wenger at Lattice2001(chiral

Linear systems solvers - recent developments and implications for lattice computations

We review the numerical analysis' understanding of Krylov subspace methods for solving (non-hermitian) systems of equations and discuss its implications for lattice gauge theory computations using the example of the Wilson fermion matrix. Our thesis is that mature methods like QMR, BiCGStab or restarted GMRES are close to optimal for the Wilson fermion matrix. Consequently, preconditioning appears to be the crucial issue for further improvements.Comment: 7 pages, LaTeX using espcrc2.sty, 2 figures, 9 eps-files, Talk presented at LATTICE96(algorithms), submitted to Nucl. Phys. B, Proc. Supp