[petsc-users] Singular Eigenproblem with SLEPc

[Nidish]

Hello,

I'm presently working with a large finite element model with several 
RBE3 constraints with "virtual" 6DOF nodes in the model.

I have about ~36000 3DOF nodes making up my model and about ~10 RBE3 
virtual nodes (which have zero intrinsic mass and stiffness). I've 
extracted the matrices from Abaqus.

The way these constraints are implemented is by introducing static 
linear constraints (populating the stiffness matrix) and padding the 
mass matrix with zero rows and columns in the rows corresponding to the 
virtual nodes. So this leaves me with an eigenproblem of the form,

K.v = lam*M.v

where M is singular but the eigenproblem is well defined. Abaqus seems 
to solve this perfectly well, but after exporting the matrices, I'm 
struggling to get slepc to solve this. The manual talks about deflation, 
etc., but I couldn't really understand too much.

Is there any example code for such a case with a singular matrix where 
these procedures are carried out? Or could you provide 
references/guidances for approaching the problem?

Thank you,
Nidish