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Comparison theorems and variable speed waves for a scalar reaction–diffusion equation

Published online by Cambridge University Press:  12 July 2007

Alison L. Kay
Affiliation:
Department of Mathematics, University of Reading, Whiteknights, Reading RG6 6AX, UK ([email protected])
Jonathan A. Sherratt
Affiliation:
Centre for Theoretical Modelling in Medicine, Department of Mathematics, Heriot-Watt University, Edinburgh EH14 4AS, UK ([email protected])
J. B. McLeod
Affiliation:
Department of Mathematics, University of Pittsburgh, Pittsburgh, PA 15260, USA ([email protected])

Abstract

This paper concerns the reaction-diffusion equation ut = uxx + u2(1 − u). Previous numerical solutions of this equation have demonstrated various different types of wave front solutions, generated by different initial conditions. In this paper, the authors use a phase-plane form of comparison theorems for partial differential equations (PDEs) to confirm analytically these numerical results. In particular, they show that initial conditions with an exponentially decaying tail evolve to the unique exponentially decaying travelling wave, while initial conditions with algebraically decaying tails evolve either to an algebraically decaying travelling wave, or to the exponentially decaying wave, or to a perpetually accelerating wave, dependent upon the exact form of the decay of the initial conditions. We then focus on the case of accelerating waves and investigate their form in more detail, by approximating the full equation in this case with a hyperbolic PDE, which we solve using the method of characteristics. We use this approximate solution to derive a leading-order approximation to the wave speed.

Type
Research Article
Copyright
Copyright © Royal Society of Edinburgh 2001

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