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Monte Carlo Methods in Practice and Efficiency Enhancements via Parallel Computation


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Type

Thesis

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Authors

Marie D'Avigneau, Alix 

Abstract

Monte Carlo methods are crucial when dealing with advanced problems in Bayesian inference. Indeed, common approaches such as Markov chain Monte Carlo (MCMC) and sequential Monte Carlo (SMC) can be endlessly adapted to tackle the most complex problems. What is important then is to construct efficient algorithms, and significant attention in the literature is devoted to developing algorithms that mix well, have low computational complexity and can scale up to large datasets. One of the most commonly used and straightforward approaches is to speed up Monte Carlo algorithms by running them in parallel computing environments. The compute time of Monte Carlo algorithms is random and can vary depending on the current state of the Markov chain. Other computing-infrastructure related factors, such as competing jobs on the same processor, or memory bandwidth, which are prevalent in shared computing architectures such as cloud computing, can also affect this compute time. However, many algorithms running in parallel require the processors to communicate every so often, and for that we must ensure that they are simultaneously ready and any idle wait time is minimised. This can be done by employing a framework known as Anytime Monte Carlo, which imposes a real-time deadline on parallel computations. The contributions in this thesis include novel applications of the Anytime framework to construct efficient Anytime MCMC and SMC algorithms which make use of parallel computing in order to perform inference for advanced problems. Examples of such problems investigated include models in which the likelihood cannot be evaluated analytically, and changepoint models, which are often used to model the heterogeneity of sequential data, but tricky to infer upon due to the unknown number and locations of the changepoints. This thesis also focuses on the difficult task of performing parameter inference in single-molecule microscopy, a category of models in which the arrival rate of observations is not uniformly distributed and measurement models have complex forms. These issues are exacerbated when molecules have trajectories described by stochastic differential equations. The original contributions of this thesis are organised in Chapters 4-6. Chapter 4 shows the development of a novel Anytime parallel tempering algorithm and demonstrates the performance enhancements the Anytime framework brings to parallel tempering, an algorithm, which runs multiple interacting MCMC chains in order to more efficiently explore the state space. In Chapter 5, a general Anytime SMC sampler is developed for performing changepoint inference using reversible jump MCMC (RJ-MCMC), an algorithm that takes into account the unknown number of changepoints by including transdimensional MCMC updates. The workings of the algorithm are illustrated on a particularly complex changepoint model, and once again the improvements in performance brought by employing the Anytime framework are demonstrated. Chapter 6 moves away from the Anytime framework, and presents a novel and general SMC approach to performing parameter inference for molecules with stochastic trajectories.

Description

Date

2020-10-31

Advisors

Singh, Sumeetpal Sidhu

Keywords

Monte Carlo, Sequential Monte Carlo, SMC, Markov Chain Monte Carlo, MCMC, Particle filtering, Particle Smoothing, Anytime Monte Carlo, Approximate Bayesian Computation, Parallel Tempering, Reversible Jump Markov Chain Monte Carlo, Reversible Jump MCMC, RJ-MCMC, Single Molecule Microscopy, Fluorescence Microscopy

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Sponsorship
EPSRC (1766519)