Introduction
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The operator DYNA_VIBRA makes it possible to perform a transient or harmonic response calculation on a physical or reduced basis (called a modal base by misuse of language).

It is dedicated to linear models, but a particularity has been introduced for the study of structures with localized nonlinearities where the analysis is done on a reduced basis, supposed to represent the behavior of the structure in the frequency band of interest.

Taking this nonlinearity into account is only available for a transient response calculation on a modal basis. In *Code_Aster*, this corresponds to BASE_CALCUL = 'GENE' and TYPE_CALCUL = 'TRAN'.