OK, that's clear, thank you! David
On Tue, Mar 8, 2022 at 11:43 AM Jed Brown <j...@jedbrown.org> wrote: > I think SNESLineSearchApply_Basic will clarify these points. Note that the > pre-check is applied before "taking the step", so X is x_k. You're right > that the sign is flipped on search direction Y, as it's using -lambda below. > > /* precheck */ > ierr = SNESLineSearchPreCheck(linesearch,X,Y,&changed_y);CHKERRQ(ierr); > > /* update */ > ierr = VecWAXPY(W,-lambda,Y,X);CHKERRQ(ierr); > [...] > ierr = VecCopy(W, X);CHKERRQ(ierr); > > David Knezevic <david.kneze...@akselos.com> writes: > > > We're using SNESLinesearchPrecheck in order to implement some nonlinear > > continuation methods, and we had a couple of questions: > > > > 1. The "search direction" that is handed to the pre-check function is > > referred to as "y" in the documentation. We had assumed that we would > have > > "y = delta_x_k", where delta_x_k is as shown in the attached screenshot > > from the PETSc manual. But after doing some testing it seems that in fact > > we have "y = -delta_x_k", i.e. y is the NEGATIVE of the Newton step. Is > > this correct? > > > > 2. In the documentation for SNESLineSearchPreCheck it says that "x" is > the > > "current solution". Referring again to the attached screenshot, does this > > mean that it's x_k+1 or x_k? I assume it means x_k+1 but I wanted to > > confirm this. > > > > Thanks for your help! > > > > Regards, > > David >
