[4] GILLES L, VOGEL C, ELLERBROEK B. Multigrid preconditioned conjugate gradient method for large-scale wave-front reconstruction [J] . JOSA, 2002, A 19(9): 1817-1822.

[5] VAN D, VORST H. Iterative solution methods for certain sparse linear systems with a nonsymmetric matrix arising from PDE-problems [J]. Journal of Computational Physics, 1981, 44(1): 1-19.

[6] VAN D, VORST H. Bi-CGSTAB: A fast and smoothly converging variant of BI-CG for the solution of nonsymmetric linear systems [J]. SIAM J. Sci. Stat. Comput. 1992, 13(2): 631-644.