A Spectral Method with Harmonic Map for Elliptic PDEs on General Two-Dimensional Domains

Abstract In this paper, we develop an efficient Fourier-Legendre spectral-Galerkin method for solving elliptic partial differential equations on general two-dimensional domains. A key core of our approach is employing a harmonic map to handle the general physical domains. This technique ensures broad geometric applicability, making the method highly effective for both complex star-shaped and nonstar-shaped domains. Moreover, this method is rigorously proved, with optimal convergence results established under $$H^1$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>H</mml:mi> <mml:mn>1</mml:mn> </mml:msup> </mml:math> -norm, which is independent of the domain boundary’s smoothness. The effectiveness and generality of the scheme are validated through some numerical examples on a wide variety of complex geometries.