On Tue, Mar 14, 2023 at 12:11 PM Barry Smith <[email protected]> wrote:
> > Matt can help you more directly. > > Barry > > > On Mar 14, 2023, at 11:40 AM, Jonathan Davud Razi Seyed Mirpourian < > [email protected]> wrote: > > Dear Barry, > > Thank you very much for the quick answer! > > To my understanding, in the snes examples, it is the call: > DMPlexSetSnesLocalFEM that takes care of computing the identities important > for snes (jacobian, residual, boundary values). > Is there an equivalent for KSP (just computing the system Matrix A and the > rhs b)? I cannot find any DMPlexSetKSPLocalFEM in the docs or am I missing > something? > > Also, I was not aware of SNESKSP, so thank you very much for that, it will > be my fallback strategy. > > There are no KSP analogues. The intent is for you to use -snes_type ksp for truly linear problems. Thanks, Matt > All the best, > Jonathan > > *From:* Barry Smith <[email protected]> > *Sent:* 14. marts 2023 16:18 > *To:* Jonathan Davud Razi Seyed Mirpourian <[email protected]> > *Cc:* [email protected] > *Subject:* Re: [petsc-users] Dmplex+PetscFe+KSP > > > KSP/SNES do not automatically assemble the linear system, that is the > responsibility of DMPLEX in this case. Thus the process for assembling the > matrix is largely the same whether done with KSP or SNES and DMPLEX. The > difference is, of course, that constructing the linear matrix does not > depend on some “solution” vector as with SNES. > > Note also you can simply use SNES for a linear problem by selecting the > SNESType of SNESKSP; this will just as efficient as using KSP directly. > > You should be able to locate a SNES example and extract the calls for > defining the mesh and building the matrix but using them with KSP. > > Barry > > > > > > > On Mar 14, 2023, at 8:48 AM, Jonathan Davud Razi Seyed Mirpourian via > petsc-users <[email protected]> wrote: > > Dear Petsc team, > > I am trying to use DMplex in combination with PetscFE and KSP to solve a > linear system. > > I have struggled to do so, as all the examples I found ( for example: > https://petsc.org/release/src/snes/tutorials/ex26.c.html) use SNES. > > Is there a way to avoid this? Optimally I would like to use dmplex for the > mesh management, then create the discretization with PetscFE and then get > KSP to automatically > assemble the system matrix A. > > I hope my questions is reasonable. > > All the best, > > Jonathan > > > -- 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/>
