Preconditioned Krylov Subspace Methods for Sixth Order Compact Approximations of the Helmholtz Equation

Table 5

3D Dirichlet-Neumann problem.

Grid size (ℎ)	GMRES	SKS	Err6	Err2
1/64	8	11	4.65∗10^−06	3.67∗10^−04
1/128	5	8	6.61∗10^−08	8.74∗10^−05
1/256	4	7	1.01∗10^−09	2.17∗10^−05