[petsc-users] Solving singular systems with petsc

[Barry Smith]

  Exactly what algorithm are you using in Matlab to get the 10 smallest eigenvalues and their corresponding eigenvectors? 

  Barry


> On Aug 15, 2020, at 8:53 PM, Nidish <nb25 at rice.edu> wrote:
> 
> 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