On the convergence of shifted Laplace preconditioner combined with multilevel deflation. - Abdul Hanan Sheikh; Domenico Lahaye; Cornelis Vuik (Numer. Linear Algebra Appl., 2013)

Accelerating the shifted Laplace preconditioner for the Helmholtz equation by multilevel deflation. - Abdul Hanan Sheikh; Domenico Lahaye; L. Garcia Ramos; Reinhard Nabben; Cornelis Vuik (J. Comput. Phys., 2016)