On Mon, Dec 6, 2021 at 1:07 PM Fischer, Greg A. via petsc-users < petsc-users@mcs.anl.gov> wrote:
> With -pc_type none, my value matches the ksp value, but it no longer > converges. > So now it seems like the check with unpreconditioned residuals was not right somehow. THanks, Matt > -----Original Message----- > From: Jed Brown <j...@jedbrown.org> > Sent: Monday, December 6, 2021 12:31 PM > To: Fischer, Greg A. <fisch...@westinghouse.com>; Fischer, Greg A. via > petsc-users <petsc-users@mcs.anl.gov>; petsc-users@mcs.anl.gov > Cc: Fischer, Greg A. <fisch...@westinghouse.com> > Subject: RE: [petsc-users] KSPBuildResidual and KSPType compatibility > > [External Email] > > Please try with -pc_type none. > > There is always a small difference due to using the recurrence, but it > should be small so long as the Krylov basis is close to orthogonal. > > I'd note that if you're using this expensive convergence test, then IBCGS > probably isn't helping over BCGS (the I part is to amortize some vector and > reduction costs). It'd be worth comparing when you use normal BCGS. > > "Fischer, Greg A." <fisch...@westinghouse.com> writes: > > > I tried your suggestion, but the values are still quite different. > > > > -----Original Message----- > > From: Jed Brown <j...@jedbrown.org> > > Sent: Monday, December 6, 2021 12:01 PM > > To: Fischer, Greg A. via petsc-users <petsc-users@mcs.anl.gov>; > petsc-users@mcs.anl.gov > > Cc: Fischer, Greg A. <fisch...@westinghouse.com> > > Subject: Re: [petsc-users] KSPBuildResidual and KSPType compatibility > > > > [External Email] > > > > "Fischer, Greg A. via petsc-users" <petsc-users@mcs.anl.gov> writes: > > > >> Hello petsc-users, > >> > >> I would like to check convergence against the infinity norm, so I > defined my own convergence test routine with KSPSetConvergenceTest. (I > understand that it may be computationally expensive.) > >> > >> I would like to do this with the "ibcgs" method. When I use > KSPBuildResidual and calculate the NORM_2 against the output vector, I get > a value that differs from the 2-norm that gets passed into the convergence > test function. However, when I switch to the "gcr" method, the value I > calculate matches the function input value. > > > > IBCGS uses the preconditioned norm by default while GCR uses the > unpreconditioned norm. You can use -ksp_norm_type unpreconditioned or > KSPSetNormType() to make IBCGS use unpreconditioned. > > > >> Is the KSPBuildResidual function only compatible with a subset of the > KSPType methods? If I want to evaluate convergence against the infinity > norm, do I need to set KSPSetInitialGuessNonzero and continually re-start > the solver with a lower tolerance values until I get a satisfactory value > of the infinity norm? > >> > >> Thanks, > >> Greg > >> > >> > >> ________________________________ > >> > >> This e-mail may contain proprietary information of the sending > organization. Any unauthorized or improper disclosure, copying, > distribution, or use of the contents of this e-mail and attached > document(s) is prohibited. The information contained in this e-mail and > attached document(s) is intended only for the personal and private use of > the recipient(s) named above. If you have received this communication in > error, please notify the sender immediately by email and delete the > original e-mail and attached document(s). > > > > ________________________________ > > > > This e-mail may contain proprietary information of the sending > organization. Any unauthorized or improper disclosure, copying, > distribution, or use of the contents of this e-mail and attached > document(s) is prohibited. The information contained in this e-mail and > attached document(s) is intended only for the personal and private use of > the recipient(s) named above. If you have received this communication in > error, please notify the sender immediately by email and delete the > original e-mail and attached document(s). > > ________________________________ > > This e-mail may contain proprietary information of the sending > organization. Any unauthorized or improper disclosure, copying, > distribution, or use of the contents of this e-mail and attached > document(s) is prohibited. The information contained in this e-mail and > attached document(s) is intended only for the personal and private use of > the recipient(s) named above. If you have received this communication in > error, please notify the sender immediately by email and delete the > original e-mail and attached document(s). > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>