[petsc-users] Solving singular systems with petsc

[Nidish]

The section on solving singular systems in the manual starts with 
assuming that the singular eigenvectors are already known.

I have a large system where finding the singular eigenvectors is not 
trivially written down. How would you recommend I proceed with making 
initial estimates? In MATLAB (with MUCH smaller matrices), I conduct an 
eigensolve for the first 10 smallest eigenvalues and take the 
eigenvectors corresponding to the zero eigenvalues from this. This 
approach doesn't work here since I'm unable to use SLEPc for solving

K.v = lam*M.v

for cases where K is positive semi-definite (contains a few "rigid body 
modes") and M is strictly positive definite.

I'd appreciate any assistance you may provide with this.

Thank you,
Nidish