# David Bevan

Lecturer B

### Personal Statement

I am a Lecturer in Combinatorics in the Department of Computer and Information Sciences.

My research interests are in enumerative and extremal combinatorics, particularly in relation to permutation classes.

Enumerative combinatorics is concerned with counting, either exactly or approximately, the number of discrete structures satisfying certain constraints. Extremal combinatorics concerns determining the size of the largest possible discrete structures having given properties.

In the 1980s, following undergraduate studies in mathematics at the University of Oxford, I undertook some computer science research. For my Oxford M.Sc. dissertation, I developed a model for the denotational semantics of the concurrent programming language occam. Following this, I spent two years in industry, during which I produced a paper that introduced weighted reference counting, now a key method for managing memory in distributed computer architectures.

This was followed by a career in software development, first as a developer, consultant and trainer, based in Papua New Guinea, and subsequently as a software engineer and development manager in the UK.

In my spare time, I carried out some independent mathematical research resulting in the publication of a paper improving on a long-standing extremal result of Erdős and Füredi in discrete geometry. In 2012, I left software development for full-time mathematical research, and in 2015 was awarded a PhD from The Open University. The topic of my thesis was the growth of permutation classes. Following a year as a Visiting Research Fellow and Associate Lecturer at The Open University, I took up my current position in September 2016.

### Teaching Interests

My current teaching includes the following:

**CS103 Machines, Languages and Computation**

Propositional logic and proofs using natural deduction; normal forms and satisfiability; computational complexity, P and NP; finite state automata and regular expressions, the Brzozowski algebraic method and the pumping lemma; Turing machines, undecidability, the halting problem and the *Entsheidungsproblem**.*

**CS104 Information and Information Systems (Module 1: Information Theory)**

Data and information (syntax and semantics, text encodings, Unicode and UTF-8); error detection and correction (repetition codes, parity bits and Hamming codes); data compression (run-length encoding, Huffman coding and LZW); measuring information (entropy) and Shannon's Source Coding Theorem.

### Research Interests

My research interests concern aspects of enumerative, asymptotic and extremal combinatorics, particularly with relation to permutations.

#### Preprints

- A structural characterisation of Av(1324) and new bounds on its growth rate (with Robert Brignall, Andrew Elvey Price and Jay Pantone).
- Prolific permutations and permuted packings: downsets containing many large patterns (with Cheyne Homberger and Bridget Tenner), to appear in
*J. Combin. Theory A*.

#### Recent publications

- Staircases, dominoes, and the growth rate of 1324-avoiders (with Robert Brignall, Andrew Elvey Price and Jay Pantone),
*Electron. Notes in Discrete Math.*, 61: 123-129, 2017. - Large butterfly Cayley graphs and digraphs,
*Discrete Math*., 340(10):2432-2436, 2017. - The permutation class Av(4213,2143),
*Discrete Math. & Theor. Comput. Sci*., 18(2): #10, 2017. - Intervals of permutation class growth rates,
*Combinatorica*, 2017. - Large circulant graphs of fixed diameter and arbitrary degree (with Grahame Erskine and Rob Lewis),
*Ars Mathematica Contemporanea*, 13(2):275–291, 2017. - Pattern avoidance in forests of binary shrubs (with Derek Levin, Peter Nugent, Jay Pantone, Lara Pudwell, Manda Riehl and ML Tlachac),
*Discrete Math. & Theor. Comput. Sci*., 18(2), #8, 2016. - The permutation classes Av(1234,2341) and Av(1243,2314),
*Australasian J. Combin.*, 64(1):3–20, 2016. - Permutations avoiding 1324 and patterns in Łukasiewicz paths,
*J. London Math. Soc.*, 92(1):105–122, 2015. - Growth rates of permutation grid classes, tours on graphs, and the spectral radius,
*Trans. Amer. Math. Soc.*, 367(8):5863–5889, 2015. - Growth rates of geometric grid classes of permutations,
*Electron. J. Combin.*, 21(4): P4.51, 2014. - Sets of points determining only acute angles and some related colouring problems,
*Electron. J. Combin.*, 13(1): R12, 2006.

Details of all my publications can be found on my Google Scholar page.

#### Slides from talks

- Staircases, dominoes and leaves: Bounds on gr(Av(1324)), 29 June 2017, at Permutation Patterns 2017, Reykjavík University.
- Prolific permutations and permuted packings, 25 April 2017, at Scottish Combinatorics Meeting, University of St Andrews.
- Expansions in non-integer bases and intervals of permutation class growth rates, 9 March 2015, University of Florida.
- The matching polynomial and geometric grid classes of permutations, 3 March 2015 at 46th Southeastern International Conference on Combinatorics, Graph Theory, and Computing, Florida Atlantic University.
- Two problems in discrete geometry, 17 December 2014, The Open University.
- A fast-growing subset of Av(1324), 7 July 2014 at Permutation Patterns 2014, East Tennessee State University.
- Permutation grid classes and the spectra of graphs, 4 July 2013 at 24th British Combinatorial Conference, Royal Holloway University of London.
- Enumerative combinatorics, 14 March 2013, The Open University.
- Skinny permutation grid classes, 17 August 2012 at 22nd Postgraduate Combinatorial Conference, University of Warwick.

#### Mathematica demonstrations

## Publications

(13)## Large butterfly Cayley graphs and digraphs

Research output: Contribution to journal › Article

## Prolific permutations and permuted packings: downsets containing many large patterns

Research output: Contribution to journal › Article

## Staircases, dominoes, and the growth rate of 1324-avoiders

Research output: Contribution to journal › Conference Contribution

## Activities

(2)## 26th British Combinatorial Conference

Activity: Participating in or organising an event › Organiser of major conference

## Permutation Patterns 2015

Activity: Participating in or organising an event › Organiser of major conference