85,803 research outputs found
Adaptive multi-stage integrators for optimal energy conservation in molecular simulations
We introduce a new Adaptive Integration Approach (AIA) to be used in a wide
range of molecular simulations. Given a simulation problem and a step size, the
method automatically chooses the optimal scheme out of an available family of
numerical integrators. Although we focus on two-stage splitting integrators,
the idea may be used with more general families. In each instance, the
system-specific integrating scheme identified by our approach is optimal in the
sense that it provides the best conservation of energy for harmonic forces. The
AIA method has been implemented in the BCAM-modified GROMACS software package.
Numerical tests in molecular dynamics and hybrid Monte Carlo simulations of
constrained and unconstrained physical systems show that the method
successfully realises the fail-safe strategy. In all experiments, and for each
of the criteria employed, the AIA is at least as good as, and often
significantly outperforms the standard Verlet scheme, as well as fixed
parameter, optimized two-stage integrators. In particular, the sampling
efficiency found in simulations using the AIA is up to 5 times better than the
one achieved with other tested schemes
Orthogonal parallel MCMC methods for sampling and optimization
Monte Carlo (MC) methods are widely used for Bayesian inference and
optimization in statistics, signal processing and machine learning. A
well-known class of MC methods are Markov Chain Monte Carlo (MCMC) algorithms.
In order to foster better exploration of the state space, specially in
high-dimensional applications, several schemes employing multiple parallel MCMC
chains have been recently introduced. In this work, we describe a novel
parallel interacting MCMC scheme, called {\it orthogonal MCMC} (O-MCMC), where
a set of "vertical" parallel MCMC chains share information using some
"horizontal" MCMC techniques working on the entire population of current
states. More specifically, the vertical chains are led by random-walk
proposals, whereas the horizontal MCMC techniques employ independent proposals,
thus allowing an efficient combination of global exploration and local
approximation. The interaction is contained in these horizontal iterations.
Within the analysis of different implementations of O-MCMC, novel schemes in
order to reduce the overall computational cost of parallel multiple try
Metropolis (MTM) chains are also presented. Furthermore, a modified version of
O-MCMC for optimization is provided by considering parallel simulated annealing
(SA) algorithms. Numerical results show the advantages of the proposed sampling
scheme in terms of efficiency in the estimation, as well as robustness in terms
of independence with respect to initial values and the choice of the
parameters
Efficient Gaussian Sampling for Solving Large-Scale Inverse Problems using MCMC Methods
The resolution of many large-scale inverse problems using MCMC methods
requires a step of drawing samples from a high dimensional Gaussian
distribution. While direct Gaussian sampling techniques, such as those based on
Cholesky factorization, induce an excessive numerical complexity and memory
requirement, sequential coordinate sampling methods present a low rate of
convergence. Based on the reversible jump Markov chain framework, this paper
proposes an efficient Gaussian sampling algorithm having a reduced computation
cost and memory usage. The main feature of the algorithm is to perform an
approximate resolution of a linear system with a truncation level adjusted
using a self-tuning adaptive scheme allowing to achieve the minimal computation
cost. The connection between this algorithm and some existing strategies is
discussed and its efficiency is illustrated on a linear inverse problem of
image resolution enhancement.Comment: 20 pages, 10 figures, under review for journal publicatio
- …