2,812 research outputs found
GPS-ABC: Gaussian Process Surrogate Approximate Bayesian Computation
Scientists often express their understanding of the world through a
computationally demanding simulation program. Analyzing the posterior
distribution of the parameters given observations (the inverse problem) can be
extremely challenging. The Approximate Bayesian Computation (ABC) framework is
the standard statistical tool to handle these likelihood free problems, but
they require a very large number of simulations. In this work we develop two
new ABC sampling algorithms that significantly reduce the number of simulations
necessary for posterior inference. Both algorithms use confidence estimates for
the accept probability in the Metropolis Hastings step to adaptively choose the
number of necessary simulations. Our GPS-ABC algorithm stores the information
obtained from every simulation in a Gaussian process which acts as a surrogate
function for the simulated statistics. Experiments on a challenging realistic
biological problem illustrate the potential of these algorithms
Noise enhanced spontaneous chaos in semiconductor superlattices at room temperature
Physical systems exhibiting fast spontaneous chaotic oscillations are used to
generate high-quality true random sequences in random number generators. The
concept of using fast practical entropy sources to produce true random
sequences is crucial to make storage and transfer of data more secure at very
high speeds. While the first high-speed devices were chaotic semiconductor
lasers, the discovery of spontaneous chaos in semiconductor superlattices at
room temperature provides a valuable nanotechnology alternative. Spontaneous
chaos was observed in 1996 experiments at temperatures below liquid nitrogen.
Here we show spontaneous chaos at room temperature appears in idealized
superlattices for voltage ranges where sharp transitions between different
oscillation modes occur. Internal and external noises broaden these voltage
ranges and enhance the sensitivity to initial conditions in the superlattice
snail-shaped chaotic attractor thereby rendering spontaneous chaos more robust.Comment: 6 pages, 4 figures, revte
Accelerating delayed-acceptance Markov chain Monte Carlo algorithms
Delayed-acceptance Markov chain Monte Carlo (DA-MCMC) samples from a
probability distribution via a two-stages version of the Metropolis-Hastings
algorithm, by combining the target distribution with a "surrogate" (i.e. an
approximate and computationally cheaper version) of said distribution. DA-MCMC
accelerates MCMC sampling in complex applications, while still targeting the
exact distribution. We design a computationally faster, albeit approximate,
DA-MCMC algorithm. We consider parameter inference in a Bayesian setting where
a surrogate likelihood function is introduced in the delayed-acceptance scheme.
When the evaluation of the likelihood function is computationally intensive,
our scheme produces a 2-4 times speed-up, compared to standard DA-MCMC.
However, the acceleration is highly problem dependent. Inference results for
the standard delayed-acceptance algorithm and our approximated version are
similar, indicating that our algorithm can return reliable Bayesian inference.
As a computationally intensive case study, we introduce a novel stochastic
differential equation model for protein folding data.Comment: 40 pages, 21 figures, 10 table
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