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Applied mathematics, nonlinear and complex systems research

Explore the work we're doing in this area of expertise, one of two within our Mathematics research

The world is governed by simple laws of physics, but the consequences of these laws is far from simple.

We see immense complexity and beauty around us, and our researchers are studying how this complexity and order arises from simple rules. Through our research, we're trying to understand the world around us, and finding new ways to make it better – with our applied mathematicians currently working on applications in diverse areas including engineering, biology, and medicine.


Our work spans many topics – from the highly abstract, to intensely practical – including the following:

  • Nonlinear Dynamics, Dynamical Systems, Chaos, Renormalisation.
  • Hamiltonian Dynamics, Integrability, Chaos and Integrability from an algebraic viewpoint.
  • Mathematical Biology, Cancer, Medicine, Mathematical Epidemiology, Theoretical Ecology, Differential Equations, Delay Differential Equations.
  • Statistical Physics, Complex Systems, Game Theory, Population Dynamics, Collective Behaviour, Networks.
  • Geodesics, Differential Geometry, Geometry and Chaos, Astrodynamics (e.g., Solar Sails).
  • Homotopy theory, general topology, category theory, applications.
  • Ultra-discrete and Tropical Mathematics

Explore our major research topics

The symmetric barrier billiard system was first introduced by Wiersig, and is an example of a pseudo-integrable dynamical system: a system which consists of multiple copies of an integrable Hamiltonian system, but which itself is not integrable. The motion consists of a particle moving at constant speed inside a rectangle experiencing specular collisions with the boundary (think of a screensaver), but with a partial barrier placed centrally which splits the configuration space into two chambers.

It can be shown that the system can be completely understood by studying the transitions between these two chambers, and this leads to analysis of the autocorrelation function. For a particle moving at with slope equal to the golden mean, we have shown using a renormalization analysis that the correlations at Fibonacci times chaotically explore an invariant surface. Our current aim is to construct a model space which completely describes the behaviour of the renormalization operator which gives rise to this phenomena.

In the realm of Dynamical Systems, an important problem is to decide whether a given system is “solvable” in a reasonably simple manner. If so, the system is usually called “integrable”. Otherwise, its evolution with respect to time is generally unpredictable and very sensitive to initial conditions (a phenomenon commonly known as chaos). One concept is not intrinsically antonymous with the other, but there seems to be indeed an inverse correlation between the two in practical examples.

We currently use Galois theory, monodromy, Stokes’ theorem, and more recently formal calculus and infinite dimensional linear operators as tools to find intrinsic algebraic structures and settings characterising dynamical systems.

Geodesics are the “straight lines” of curved surfaces, and even on apparently simple surfaces the behaviour of geodesics can be very complex. Recent work established the chaotic nature of geodesics on surfaces defined in terms of spherical harmonics, and current work focuses on the conjugate locus and in particular its bifurcations.

Mathematical models are of major importance in understanding biological and medical systems. Infectious diseases, plant-soil-atmosphere interactions, cancer cells dynamics are all examples of successful synergy between mathematics and biological understanding. Analysis of these models reveals the connections between system components, the effects of these connections, and predicts how the system will evolve if changes in its components occur.

From ecosystems to chemical reactors to computer networks, many natural and artificial systems have a network structure - individual elements communicate with each other and some collective behaviour emerges. But to what extent does the network architecture of such a system determine whether behaviours such as "switching", oscillation, or chaos are allowed? In fact, using analytical, algebraic and geometric approaches, a surprising amount can be said about the dynamics of networks from the network structure alone, and without computer simulation.

On the smallest length scales, and at low temperatures, physical matter acts in ways that are different to those of our everyday experience. The gas Helium, for example, when cooled to sufficiently low temperatures undergoes a change of state and becomes a superfluid, exhibiting highly unusual properties. Tiny droplets of superfluid Helium, in which different types of molecules have been dissolved, might in the future have a wide range of uses.

Quantum Mechanics provides mathematical techniques that can be used to understand the behaviour of materials like this. The pictures illustrate a recent "Bosons on a Ring (BoaR)" model, in which a single central molecule is surrounded by a ring of Helium atoms. The work aims to answer the following question: since superfluidity is a property exhibited by "bulk" liquid Helium, rather than single atoms, how few atoms can be present in order for the phenomenon to occur?

A Solar Sail is a novel type of spacecraft, which uses sunlight for its propulsion. Solar sails are capable of unusual orbits and missions which conventional spacecraft are not. Recent work has focused on the periodic orbits of solar sails in the Earth-Sun system, and in particular their stability.

The goal of Statistical Physics is to understanding how the interactions between the individual, sometimes microscopic, elements of physical systems leads to the emergence of large scale properties such as pattern, order and dramatic changes in state. Our recent work has focused on understanding how collective behaviour of groups of agents playing games (competing for the best investments, searching for the best territory) can emerge from simple models of their intelligence.

We also use ideas from statistical physics to understand how certain unusual rock formations appear, and why the distributions of landslide sizes and disease outbreaks may have a 'double pareto' distribution due to shocks in the processes which drive them. This work has led to the discovery of some new families of Stochastic Jump Processes.

Objects called strange non-chaotic attractors (SNAs) can arise in the study of quasiperiodically forced systems, and are fractal sets upon which nearby trajectories do not separate exponentially (on average). These seemingly paradoxical objects have been of great interest over the past three decades, after first being shown to exist in a paper by Grebogi et al. in 1984.

Our recent contribution to this topic has been in the exploration of the “non-smooth pitchfork bifurcation”. In particular, we have examined scaling properties and the box-counting dimension of attractors arising from this route to SNA. One of the key ingredients in this analysis is the technique of renormalization, which can be used under certain circumstances to show self-similarity of the attractors and to calculate scaling factors describing their growth near the point of transition.

Discover our areas of expertise

Applied mathematics, nonlinear and complex systems is one of our 2 areas of research expertise in Mathematics – explore the other area below.

Industrial mathematics

Industrial mathematics

We're using modelling and mathematical analysis to find new ways of improving practices across a range of areas in science and industry – including renewable energy.
Read more

Research groups

Interested in a PhD in Mathematics?

Browse our postgraduate research degrees – including PhDs and MPhils – at our Mathematics postgraduate research degrees page.