So left preconditioning converges fine, the true residual gets as small as one could expect. Right preconditioning fails completely; I have no explanation for this, could be a bug in the PETSc implementation for right preconditioning with this method.
What do you get with -ksp_type bcgs both left and right preconditioning? Barry > On Dec 7, 2021, at 4:25 PM, Fischer, Greg A. <[email protected]> > wrote: > > I’ve attached typical examples of “A” and “b”. Do these qualify as large > values? > > The two runs are with and without “-ksp_pc_side right”. > > From: Barry Smith <[email protected] <mailto:[email protected]>> > Sent: Tuesday, December 7, 2021 3:44 PM > To: Fischer, Greg A. <[email protected] > <mailto:[email protected]>> > Cc: Fischer, Greg A. via petsc-users <[email protected] > <mailto:[email protected]>> > Subject: Re: [petsc-users] KSPBuildResidual and KSPType compatibility > > [External Email] > > When the preconditioned and non-preconditioner residual norms as so hugely > different this usually indicates something is badly scaled or something "bad" > is happening within the preconditioner. > > 0 KSP preconditioned resid norm 2.434689662304e-01 true resid norm > 1.413757649058e+09 ||r(i)||/||b|| 1.442188243865e-04 > .... > 19 KSP preconditioned resid norm 4.505576228085e-15 true resid norm > 1.810377537457e-02 ||r(i)||/||b|| 1.846784138157e-15 > > notice that at the end the true residual is not particularly small. Is your b > really big and does the matrix have really large values in it? > > What are the two runs? Left and right preconditioning with ibcgs or something > else? > > > On Dec 7, 2021, at 12:44 PM, Fischer, Greg A. <[email protected] > <mailto:[email protected]>> wrote: > > Attached are outputs with these options. > > What should I make of these? > > From: Barry Smith <[email protected] <mailto:[email protected]>> > Sent: Monday, December 6, 2021 2:16 PM > To: Fischer, Greg A. via petsc-users <[email protected] > <mailto:[email protected]>> > Cc: Fischer, Greg A. <[email protected] > <mailto:[email protected]>> > Subject: Re: [petsc-users] KSPBuildResidual and KSPType compatibility > > [External Email] > > What do you get for -ksp_type ibcgs -ksp_monitor -ksp_monitor_true_residual > > with and without -ksp_pc_side right ? > > > > > On Dec 6, 2021, at 12:00 PM, Jed Brown <[email protected] > <mailto:[email protected]>> wrote: > > "Fischer, Greg A. via petsc-users" <[email protected] > <mailto:[email protected]>> 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). > <ksp-monitor_output.txt><ksp-monitor_output-pc_side_right.txt> > > > > 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). > <typ_A.txt><typ_b.txt>
