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

Table 2

1D Dirichlet problem.

Grid size (ℎ)	GMRES	SKS	CA	Err6	Err2
1/32	6	8	6	3.88∗10^−03	1.16∗10^−01
1/64	4	4	5	5.08∗10^−05	2.4∗10^−02
1/128	3	3	4	7.61∗10^−7	5.7∗10^−03
1/258	3	3	3	1.14∗10^−8	1.4∗10^−03