[petsc-users] [SLEPc] non-deterministic behaviour in GHEP with Krylov-Schur

[Jose E. Roman]

> El 8 mar 2016, a las 11:28, Denis Davydov <davydden at gmail.com> escribió:
> 
> Dear all,
> 
> I have some issues with Krylov-Schur applied to GHEP, namely, that different runs on the same machine with the
> same number of MPI cores gives different eigenvectors results.
> Here is an example:
> 
> mass.InfNorm =15.625
> stiff.InfNorm=726.549
> eigenfunction[0].linf=0.459089
> eigenfunction[1].linf=0.318075
> eigenfunction[2].linf=0.326199
> eigenfunction[3].linf=0.312521
> eigenfunction[4].linf=0.271712
> eigenfunction[5].linf=0.280744
> eigenfunction[6].linf=0.315654
> eigenfunction[7].linf=0.192715
> eigenfunction[8].linf=0.194826
> 
> vs
> 
> mass.InfNorm =15.625
> stiff.InfNorm=726.549
> eigenfunction[0].linf=0.459089
> eigenfunction[1].linf=0.329682
> eigenfunction[2].linf=0.326199
> eigenfunction[3].linf=0.325289
> eigenfunction[4].linf=0.284252
> eigenfunction[5].linf=0.263418
> eigenfunction[6].linf=0.315756
> eigenfunction[7].linf=0.194826
> eigenfunction[8].linf=0.193074
> 
> Eigensolver tolerance is absolute and 1e-20. So it’s a bit surprising that there is a quite a big variation in L-inf norm of eigenvectors (0.318075 vs 0.329682).
> In either case, the biggest issue is non-deterministic behaviour.
> Is there anything I am missing in Krylov-Schur to make its behaviour as deterministic as possible?
> 
> p.s. shift-and-invert is done with LU from MUMPS. Shift value is lower than the exact lowest eigenvalue.
> 
> Kind regards,
> Denis 
> 

Which are the eigenvalues?