  In this work, we study the quasinormal modes of Schwarzschild and
Schwarzschild (Anti-) de Sitter black holes by a matrix method. The proposed
method involves discretizing the master field equation and expressing it in
form of a homogeneous system of linear algebraic equations. The resulting
homogeneous matrix equation furnishes a non-standard eigenvalue problem, which
can then be solved numerically to obtain the quasinormal frequencies. A key
feature of the present approach is that the discretization of the wave function
and its derivatives are made to be independent of any specific metric through
coordinate transformation. In many cases, it can be carried out beforehand
which in turn improves the efficiency and facilitates the numerical
implementation. We also analyze the precision and efficiency of the present
method as well as compare the results to those obtained by different
approaches.
