High-order matrix method with delimited expansion domain

Abstract Motivated by the substantial instability of fundamental and high-overtone quasinormal modes (QNMs), recent developments regarding notion black hole pseudospectrum call for numerical results with unprecedented precision. This work generalizes improves matrix method QNMs to higher orders, specifically aiming at a class perturbations metric featured discontinuity intimately associated QNM structural instability. The approach is based on mock-Chebyshev grid, which guarantees its convergence in degree interpolant. In practice, solving formidable task. presence poses further difficulty so that many well-known approaches cannot be employed straightforwardly. Compared other viable methods, modified competent speed accuracy. Therefore, serves as helpful gadget relevant studies.