SNESSetKSP() (and friends) was a mistake, it was originally introduced for symmetry reasons but doesn't seem to have a good reason to exist.
Barry > On Oct 12, 2021, at 2:24 PM, Matthew Knepley <knep...@gmail.com> wrote: > > On Tue, Oct 12, 2021 at 10:27 AM Nicolás Barnafi <nab...@gmail.com > <mailto:nab...@gmail.com>> wrote: > Thank you for the support. I rewrote the initialization in a simpler way, now > it works as expected: > > > dofmap_s = V.sub(0).dofmap().dofs(); is_s = > > PETSc.IS().createGeneral(dofmap_s) > > dofmap_p = V.sub(1).dofmap().dofs(); is_p = > > PETSc.IS().createGeneral(dofmap_p) > > snes = PETSc.SNES().create(MPI.COMM_WORLD) > > snes.setFunction(problem.F, b.vec()); snes.setJacobian(problem.J, > > J_mat.mat()) > > pc = snes.ksp.getPC() > > pc.setType('fieldsplit') > > pc.setFieldSplitIS((None, is_s), (None, is_p)) > > snes.setFromOptions() > > snes.solve(None, problem.u.vector().vec()) > > Apparently trying to setup the solver's internals is not recommended. As a > side note, I tried also setting up the KSP using 'SNESSetKSP', but this > solution is not so good as giving the command 'snes_ksp_ew' does nothing, > even though it gets correctly read as shown by snes.view(). > > I think I can explain this. The Eisenstat-Walker scheme is a way to set > tolerances for the linear solves inside a Newton iteration. The goal is > to avoid over-solving the linear systems, meaning that far away from the > solution accurate linear solves have no advantage over inaccurate ones. > Implementing this involves coordination with the linear solver since we are > setting the convergence tolerance. When you replace the linear solve, > that setup is discarded. Thus, when configuring things, we recommend that you > pull out the existing object > > SNESGetKSP() > > and customize it, rather than creating a new object and setting it. > > Thanks, > > Matt > > Thanks for the help! > Best, > Nicolas > > On Tue, Oct 12, 2021 at 4:23 PM Matthew Knepley <knep...@gmail.com > <mailto:knep...@gmail.com>> wrote: > I looked over every place we use that error code. I do not think it is coming > from PETSc, but rather from petsc4py. However, something > is eating the error message, and I think Stefano indicated. My first step > would be to get the FEniCS folks to display the error message. > > Another option is to just run it in Firedrake since I think we can see the > stack properly there. > > Thanks, > > Matt > > On Tue, Oct 12, 2021 at 8:37 AM Nicolás Barnafi <nab...@gmail.com > <mailto:nab...@gmail.com>> wrote: > Thank you Stefano for the help. I added the lines you indicated, but the > error remains the same, here goes snes.view() + error > > > SNES Object: 1 MPI processes > > type: qn > > SNES has not been set up so information may be incomplete > > type is BROYDEN, restart type is DEFAULT, scale type is JACOBIAN > > Stored subspace size: 10 > > Using the single reduction variant. > > maximum iterations=10000, maximum function evaluations=30000 > > tolerances: relative=1e-08, absolute=1e-50, solution=1e-08 > > total number of function evaluations=0 > > norm schedule ALWAYS > > SNESLineSearch Object: 1 MPI processes > > type: basic > > maxstep=1.000000e+08, minlambda=1.000000e-12 > > tolerances: relative=1.000000e-08, absolute=1.000000e-15, > > lambda=1.000000e-08 > > maximum iterations=1 > > Traceback (most recent call last): > > File "Twist.py", line 234, in <module> > > snes.setUp() > > File "PETSc/SNES.pyx", line 530, in petsc4py.PETSc.SNES.setUp > > petsc4py.PETSc.Error: error code 83 > > On Tue, Oct 12, 2021 at 2:07 PM Stefano Zampini <stefano.zamp...@gmail.com > <mailto:stefano.zamp...@gmail.com>> wrote: > > > Il giorno mar 12 ott 2021 alle ore 13:56 Nicolás Barnafi <nab...@gmail.com > <mailto:nab...@gmail.com>> ha scritto: > Hello PETSc users, > > first email sent! > I am creating a SNES solver using fenics, my example runs smoothly with > 'newtonls', but gives a strange missing function error (error 83): > > > Dolphin swallows any useful error information returned from PETSc. You can > try using the below code snippet at the beginning of your script > > from petsc4py import PETSc > from dolfin import * > # Remove the dolfin error handler > PETSc.Sys.pushErrorHandler('python') > > > > these are the relevant lines of code where I setup the solver: > > > problem = SNESProblem(Res, sol, bcs) > > b = PETScVector() # same as b = PETSc.Vec() > > J_mat = PETScMatrix() > > snes = PETSc.SNES().create(MPI.COMM_WORLD) > > snes.setFunction(problem.F, b.vec()) > > snes.setJacobian(problem.J, J_mat.mat()) > > # Set up fieldsplit > > ksp = snes.ksp > > ksp.setOperators(J_mat.mat()) > > pc = ksp.pc > > pc.setType('fieldsplit') > > dofmap_s = V.sub(0).dofmap().dofs() > > dofmap_p = V.sub(1).dofmap().dofs() > > is_s = PETSc.IS().createGeneral(dofmap_s) > > is_p = PETSc.IS().createGeneral(dofmap_p) > > pc.setFieldSplitIS((None, is_s), (None, is_p)) > > pc.setFromOptions() > > snes.setFromOptions() > > snes.setUp() > > If it can be useful, this are the outputs of snes.view(), ksp.view() and > pc.view(): > > > type: qn > > SNES has not been set up so information may be incomplete > > type is BROYDEN, restart type is DEFAULT, scale type is JACOBIAN > > Stored subspace size: 10 > > Using the single reduction variant. > > maximum iterations=10000, maximum function evaluations=30000 > > tolerances: relative=1e-08, absolute=1e-50, solution=1e-08 > > total number of function evaluations=0 > > norm schedule ALWAYS > > SNESLineSearch Object: 4 MPI processes > > type: basic > > maxstep=1.000000e+08, minlambda=1.000000e-12 > > tolerances: relative=1.000000e-08, absolute=1.000000e-15, > > lambda=1.000000e-08 > > maximum iterations=1 > > KSP Object: 4 MPI processes > > type: gmres > > restart=1000, using Modified Gram-Schmidt Orthogonalization > > happy breakdown tolerance 1e-30 > > maximum iterations=1000, initial guess is zero > > tolerances: relative=1e-05, absolute=1e-50, divergence=10000. > > left preconditioning > > using UNPRECONDITIONED norm type for convergence test > > PC Object: 4 MPI processes > > type: fieldsplit > > PC has not been set up so information may be incomplete > > FieldSplit with Schur preconditioner, factorization FULL > > I know that PC is not setup, but if I do it before setting up the SNES, the > error persists. Thanks in advance for your help. > > Best, > Nicolas > -- > Nicolás Alejandro Barnafi Wittwer > > > -- > Stefano > > > -- > Nicolás Alejandro Barnafi Wittwer > > > -- > 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/> > > > -- > Nicolás Alejandro Barnafi Wittwer > > > -- > 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/>
