Eigen analysis

[arbarbosa]

Dear All,

I realize the eigenvalues are computed when we set the [eigen $numModes] command without using the analyze command. Is it also possible to output the eigenvectors without invoking the analyze command? If not, I would like to understand why not?

Thank you

[vesna]

To perform eigen analysis you do not need to invoke the analyze command. Analyze command you should use to perform static or transient analysis. However to build a recorder, one step of analysis is needed. This is a feature of OpenSees, something that has to be changed. As of now that is how it works. So, to record eigenvectors you need at least one step of analysis. If you do not plan of doing any analysis other then eigen analysis you can perform one step of analysis with no loading. In case you have either static or dynamic analysis following the eigen analysis the recorder for eigenvectors will be created after the first step of analysis and populated after you exit opensees.

[arbarbosa]

That makes perfect sense now. Thank you for that very clear response.

[vesna]

Frank, added a recorder command to OpenSees. So, if you want to perform only eigen alnalysis and record eigenvectors, insert "record" command after eigen command.

e.g.,
set lambda [eigen $numModes];
record

This way you can avoid having one step of analysis for your recorders to be created.

[arbarbosa]

Thank you very much again.

[arbarbosa]

By the way, it might be worth changing the very nice and clear example of the eigen analysis shown available in: http://opensees.berkeley.edu/wiki/index ... hear_frame

Thanks again for the good job.

[vesna]

I did it. Thanks for pointing it out.

[uyupeng]

thanks