HELP : Modal Analysis of Piezoelectric UEL Element

Hello Experts,

I am trying to do modal analysis on user-defined piezoelectric shell element. My eigen value probelm of free vibration is given in the attachment.

My issue is Mass matrix [M] is not positive definite due to electrical degrees of freedom having no mass associated with them and the stiffness matrix [K] given is non-positive definite due to negative dielectric terms. I know , it is possible to condense out the above equations and find the real eigen values and eigen vectors but how to do this in UEL subroutine using Lanczos solver. I introduced arbitrary/artificial mass terms in Mass matrix to get the eigen values and eigen vectors. Is there any other  appropriate method? / ideas?

I need to resolve this issue asap. I would really  appreciate any help regarding this.

Thanking you in advance,

Somu