Quasinormal modes by improved matrix method and weighted residual method

Abstract This work discusses the Improved Matrix Method and Weighted Residual Method for studying the quasinormal modes (QNMs) of black holes. In the first method, by utilizing Jordan decomposition, the improved matrix method avoids the calculation of inverse matrices in the original matrix method. This significantly saves computational resources and time needed to compute the coefficient square matrices of the derivatives. In the second method, we illustrate the effectiveness of the weighted residual method in QNMs calculations by using the collocation method and Galerkin method as examples. We compared the results of both methods with the Generalized Horowitz-Hubeny Method and the WKB approximation. The methods proposed in this paper demonstrates superior precision. Additionally, we provide five criteria to exclude extraneous roots from the methods.