  We present the preliminary tests on two modifications of the Hybrid Monte
Carlo (HMC) algorithm. Both algorithms are designed to travel much farther in
the Hamiltonian phase space for each trajectory and reduce the autocorrelations
among physical observables thus tackling the critical slowing down towards the
continuum limit. We present a comparison of costs of the new algorithms with
the standard HMC evolution for pure gauge fields, studying the autocorrelation
times for various quantities including the topological charge.
