A comparison of periodic travelling wave generation by Robin and Dirichlet boundary conditions in oscillatory reaction–diffusion equations

Periodic travelling waves are an important solution form in oscillatory reaction–diffusion equations. I have shown previously that such waves arise naturally near a boundary at which a Dirichlet condition is applied. This result has applications in ecology, providing a potential explanation for the periodic waves seen in a number of natural populations. However, in ecological applications the Dirichlet boundary condition typically arises as a simple approximation to a more realistic Robin condition. In this paper, I consider the generation of periodic travelling waves by Robin boundary conditions and how the wave amplitude compares with that arising from Dirichlet conditions. I study a ‘λ–ω’ system of equations, which is the normal form of an oscillatory reaction–diffusion system with scalar diffusion matrix close to a Hopf bifurcation. I consider a Robin boundary condition close to the Dirichlet limit, with proximity measured by a small parameter , and I study the equations as a perturbation problem in this small parameter. I show that the perturbation is singular and that although the solution itself changes at O( ), the amplitude of the periodic travelling wave which this solution approaches far from the boundary is unchanged at both O( ) and O( 2). This provides strong justification for the use of the Dirichlet approximation to the Robin condition when studying periodic travelling wave generation in equations of λ–ω type. Finally, I discuss the ecological applications of the results.