Statistics and Probability
Department of Mathematical Sciences
The University of Liverpool

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Topics of projects for prospective research students.


Convex Analytic Approach to certain controlled Markov chains and jump processes.

This project is mainly theoretical. As is known, the Convex Analytic approach, dual to the Dynamic Programming approach, is convenient for the study of constrained problems. Currently, there are several particular models for which this approach is still not developed. (For instance, absorbing Markov Decision Processes with Borel spaces and jump processes with unbounded intensities.) The objective is to obtain and investigate the characteristic equation for occupation measures, find necessary and sufficient conditions of optimality and describe sufficient classes of policies in multicriteria problems.

Analysis of communication networks.

The project involves mathemtical analysis of several Active Queue Management models of TCP connection. A typical model is the continuous time Queuing System with a varying input stream of jobs (customers). Moreover, one can control the input intensity, and the goal is to find an optimal control policy. Generally speaking, such models are "piece-wise deterministic" processes, and optimal control of them is at the cutting edge of modern control theory. Another project in this field involves "Call Admission Control" where the Decision Maker must decide whether to accept or reject the newly arrived customer (job).

Approximations of controlled birth-and-death processes.

Such processes (with discrete or continuous time) appear in Queuing Theory, Reliability, Epidemiology and many other areas. In some cases, the underlying model can be approximated by a diffusion, or by a deterministic ordinary differential equation (e.g. so called "Fluid Model" of a queuing system). The objective of the project is to evaluate the accuracy of such approximations and to elaborate optimal control policies for them.

To succeed in the project and to enjoy your study you must have good background in at least two areas out of the following:

1. functional analysis (metric spaces, Lebesgue integrals and so on);
2. standard calculus (knowledge of differential equations, ordinary and partial, is an advantage);
3. basic probability (knowledge of random processes is an advantage);
4. methods of optimisation (knowledge of methods for constrained problems is an advantage);
5. computer programming (knowledge of mathematical software like MATLAB and MAPLE is an advantage).

Books to read:

1. D.Burghes, A.Graham. Control and Optimal Control Theories with Applications. Horwood Publ. Limited, 2004, ISBN: 190427501X
2. H.M.Taylor, S.Karlin. An Introduction to Stochastic Modeling. Academic Press, 1998, ISBN: 0126848874
3. M.L.Puterman. Markov Decision Processes. Wiley, 1994, ISBN: 0471619779
4. S.M.Ross. Applied Probability Models with Optimization Applications. Dover Publ. 1992, ISBN: 0486673146

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