Eigen Command - OpenSeesWiki

# Eigen Command

This command is used to perform the analysis.

 eigen <$type> <$solver> $numEigenvalues $numEigenvalues number of eigenvalues required $type optional string detailing type of eigen analysis: -standard or -generalized (default: -generalized)$solver optional string detailing type of solver: -genBandArpack, -symmSparseArpack, -symmBandLapack, -fullGenLapack, -UmfPack, -SuperLU (default: -genBandArpack)

RETURNS:

a tcl string containg eigenvalues.

NOTES:

1. The eigenvectors are stored at the nodes and can be printed out using a Node Recorder, the nodeEigenvector command, or the Print command.
2. The default eigensolver is able to solve only for N-1 eigenvalues, where N is the number of inertial DOFs. When running into this limitation the -fullGenLapack solver can be used instead of the default Arpack solver.

THEORY:

Standard Problem:

$\left (K - \lambda I \right ) \Phi = 0$

Generalized Problem:

$\left (K - \lambda M \right ) \Phi = 0$

EXAMPLE:

set eigenvalues [eigen 10];

Code Developed by: fmk