Nadir-Alexandre Messaï, Sebastien Pernet & Abdesselam Bouguerra. (2022). Directional $\mathcal{H}^2$ Compression Algorithm: Optimisations and Application to a Discontinuous Galerkin BEM for the Helmholtz Equation. Communications in Computational Physics. 31 (5). 1585-1635. doi:10.4208/cicp.OA-2021-0241