EigenValues of a Vibrating system

Hello,

I have to do a vibration analysis of a beam, but first I am calculating the eigen values of it using the formula

eigs(A,k,'smallestabs')

For my case, I have changed it to

eigs(Mass_Matrix,Stiffness_Matrix,12,'smallestabs') is it correct? or I should change it to

eigs(Stiffness_Matrix,Mass_Matrix,12,'smallestabs')

Answer 1

[Christine Tobler]

Usually for finite element problems, the stiffness matrix is passed in as the first input, and the mass matrix as the second input.

Think of it this way: If all the basis functions in your model were orthogonal to each other and normalized, the mass matrix would be an identity matrix, and you would want to calculate the eigenvalues of the stiffness matrix as a simple eigenvalue problem.