Chao Liang and Xueshuang Xiang. (2016). Convergence of an Anisotropic Perfectly Matched Layer Method for Helmholtz Scattering Problems .
            <i>Numerical Mathematics: Theory, Methods and Applications</i>. <i>9</i> (3).
            358-382.
         doi:10.4208/nmtma.2016.m1505