“…At first, they were used to accelerate computations [1], but they also allowed larger numbers of dipoles to be simulated [6,108], since storage of the entire matrix is prohibitive for direct methods. The most widely used iterative methods in the DDA are Krylov-space methods, such as [107] conjugate gradient (CG), CG applied to the Normalized equation with minimization of Residual norm (CGNR), Bi-CG, Bi-CG stabilized (Bi-CGSTAB), CG squared (CGS), generalized minimal residual (GMRES), quasi-minimal residual (QMR), transpose free QMR (TFQMR), and generalized product-type methods based on Bi-CG (GPBi-CG) [109].…”