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Continue to ChatFinite element method and step-by-step perturbation method for high frequency eigenvalue problems - https://avesis.deu.edu.tr/yonetilen-tez/10ae5f10-3b90-4639-832e-6c3e86b20554/finite-element-method-and-step-by-step-perturbation-method-for-high-frequency-eigenvalue-problems