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

Table 3

3D Dirichlet problem.

Grid size (ℎ)	GMRES	SKS	CA	Err6	Err2
1/64	5	10	23	3.03∗10^−04	4.47∗10^−06
1/128	3	6	15	8.13∗10^−05	6.35∗10^−08
1/256	3	5	14	2.06∗10^−05	9.68∗10^−10