Maximum Number of Eigenvalues

Hello,

I am looking at eigen frequencies in a simple beam. In the end I want the modal matrix and the corresponding eigen values. The error message I receive is that I can only solve for less than the number of unconstrained degrees of freedom minus 1. Which means that a bar with free-free end conditions, I can solve for 6*(number of nodes)-2 eigenvalues.

So if I broke a beam into 4 elements (5 nodes) it would have 30 degrees of freedom. it would have 30 eigenvalues. I however, can only solve for 28 of them. Which means I can also only solve for 28 eigenvectors.

My Mass and Stiffness matrices will be 30X30. My modal matrix will 30X28.

Is there a solution for this?

Any help is greatly appreciated.

Thanks,

Joshua