[petsc-users] Restarting a SLEPC run to refine an eigenvector

[Jose E. Roman]

> El 29 mar 2023, a las 9:58, LUTSKO James <Jim.Lutsko at ulb.be> escribió:
> 
> I withdraw my question. In trying to put together an example to illustrate the problem, I found thatEPSSetInitialSubspace() does indeed "work" - in the sense that the eigenvalue, which decreases monotonically during the calculation, picks up from where the previous run left off. I am not sure why I had previously thought it was otherwise.
> 
> thanks
> 

Your use case is a typical one that might have slow convergence. In Davidson-type methods it is generally better if you can use a more powerful preconditioner (jacobi is likely not helping).

If you can afford to factorize the matrix I would suggest using shift-and-invert with target=0 (or whatever is better for your application) with the default solver (Krylov-Schur). But normally factorizing a large Hamiltonian matrix is prohibitive.

If you want, send me a sample matrix and I can do some tests.

Jose