# Natural frequency extraction

 The frequency extraction procedure: performs eigenvalue extraction to calculate the natural frequencies and the corresponding mode shapes of a system; will include initial stress and load stiffness effects due to preloads and initial conditions if geometric nonlinearity is accounted for in the base state, so that small vibrations of a preloaded structure can be modeled; will compute residual modes if requested; is a linear perturbation procedure; can be performed using the traditional Abaqus software architecture if appropriate, but the high-performance SIM architecture (see Using the SIM architecture for modal superposition dynamic analyses) is used as the default; and solves the eigenfrequency problem only for symmetric mass and stiffness matrices; the complex eigenfrequency solver must be used if unsymmetric contributions, such as the load stiffness, are needed. The following topics are discussed:
 Related Topics Defining an analysis General and perturbation procedures About dynamic analysis procedures In Other Guides *FREQUENCY Configuring a frequency procedure

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