Abstract: A universal matrix perturbation technique for complex modes is presented. This technique is applicable to all the three cases of complex eigenvalues: distinct, repeated and closely spaced eigenvalues. The lower order perturbation formulas are obtained by performing two complex eigensubspace condensations, and the higher order perturbation formulas are derived by a successive approximation process. Three illustrative examples are given to verify the proposed method and satisfactory results are observed.

Key words: perturbation method, complex modes, repeated eigenvalues, closely spaced eigenvalues