PADE-Z(2) ESTIMATOR OF DETERMINANTS

We introduce the Pade-Z(2) (PZ) stochastic estimator for calculating d eterminants and determinant ratios. The estimator is applied to the ca lculation of fermion determinants from the two ends of the hybrid Mont e Carlo trajectories with pseudofermions. Our results on the 8(3) x 12 lattice with Wilson action show that the statistical errors from the stochastic estimator can be reduced by more than an order of magnitude by employing an unbiased variational subtraction scheme which utilize s the off-diagonal matrices from the hopping expansion. Having been ab le to reduce the error of the determinant ratios to about 20% with a r elatively small number of noise vectors. this may become a feasible al gorithm for simulating dynamical fermions in full QCD. We also discuss the application to the density of states in Hamiltonian systems.