Can you set up the preconditioner so that you can just use GMRES?
> On Jun 22, 2018, at 4:33 PM, Nishant Nangia <[email protected]> > wrote: > > Hi, > > I am solving a saddle point system using a shell preconditioner (which itself > uses Krylov solvers, hence the use of FGMRES). I had added the option to > re-scale parts of the saddle point system to minimize loss of floating point > precision for cases where there are varying orders of magnitude in the > system/unknowns. > > I wanted to show that re-scaling can alleviate large differences between the > preconditioned and unpreconditioned residual norms. However, I notice that > FGMRES only supports right preconditioning, meaning the preconditioned > residual is never formed/used (I think). > > Is there any way to form the preconditioned norm for FGMRES, or does it just > not make sense in the context of right-preconditioned iterative solvers? Is > there any way to show that the re-scaling is improving the solver convergence > (i.e. showing that it ensures that the true and relative residual are close > to each other)? > > Nishant Nangia > Northwestern University > Ph.D. Candidate | Engineering Sciences and Applied Mathematics > Tech L386
