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Journal of Nonlinear Science

, Volume 23, Issue 2, pp 241–282 | Cite as

Boundary Value Problems for the Elliptic Sine-Gordon Equation in a Semi-strip

  • A. S. Fokas
  • J. Lenells
  • B. Pelloni
Article

Abstract

We study boundary value problems posed in a semistrip for the elliptic sine-Gordon equation, which is the paradigm of an elliptic integrable PDE in two variables. We use the method introduced by one of the authors, which provides a substantial generalization of the inverse scattering transform and can be used for the analysis of boundary as opposed to initial-value problems. We first express the solution in terms of a 2×2 matrix Riemann–Hilbert problem whose “jump matrix” depends on both the Dirichlet and the Neumann boundary values. For a well posed problem one of these boundary values is an unknown function. This unknown function is characterised in terms of the so-called global relation, but in general this characterisation is nonlinear. We then concentrate on the case that the prescribed boundary conditions are zero along the unbounded sides of a semistrip and constant along the bounded side. This corresponds to a case of the so-called linearisable boundary conditions, however, a major difficulty for this problem is the existence of non-integrable singularities of the function q y at the two corners of the semistrip; these singularities are generated by the discontinuities of the boundary condition at these corners. Motivated by the recent solution of the analogous problem for the modified Helmholtz equation, we introduce an appropriate regularisation which overcomes this difficulty. Furthermore, by mapping the basic Riemann–Hilbert problem to an equivalent modified Riemann–Hilbert problem, we show that the solution can be expressed in terms of a 2×2 matrix Riemann–Hilbert problem whose “jump matrix” depends explicitly on the width of the semistrip L, on the constant value d of the solution along the bounded side, and on the residues at the given poles of a certain spectral function denoted by h(λ). The determination of the function h remains open.

Keywords

Elliptic sine-Gordon Boundary value problems Integrable PDEs 

Mathematics Subject Classification

35J60 35J65 35P25 

Notes

Acknowledgements

This research was partially supported by EPSRC grant EP/E022960/1. ASF would like to express his gratitude to the Guggenheim Foundation, USA.

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Copyright information

© Springer Science+Business Media New York 2012

Authors and Affiliations

  1. 1.Department of Applied Mathematics and Theoretical PhysicsCambridge UniversityCambridgeUK
  2. 2.Department of MathematicsBaylor UniversityWacoUSA
  3. 3.Department of MathematicsUniversity of ReadingReadingUK

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