“…For examples, methods based on the Fourier/spectral representation include finite difference (FD) methods [17,23,24,25,30,31,39], spectral element method [35], and sinc-based method [6]. Methods based on the singular integral representation include FD methods [14,28,36], finite element methods [1,2,3,4,8,15,37], discontinuous Galerkin methods [12,13], and spectral method [26]; and FD methods [11,32,38] based on the Grünwald-Letnikov representation. Loosely speaking, most of the existing FD methods have been constructed on uniform grids, have the advantage of efficient matrix-vector multiplication via the fast Fourier transform (FFT), but do not work for domains with complex geometries and have difficulty to incorporate with mesh adaptation.…”