Adaptive complex frequency with V-cycle GMRES for preconditioning 3D Helmholtz equation Xu, Wenhao ; Zhong, Yang ; Wu, Bangyu ; Gao, Jinghuai ; Liu, Qing Huo Abstract Publication: Geophysics Pub Date: September 2021 DOI: 10.1190/geo2020-0901.1 Bibcode: 2021Geop...86..349X