For nonlinear problems the linesearch may very well fail if the linear update is a bad descent direction (usually indicating a nonconvexity of the corresponding energy functional, if it exists; is this a p-Laplacian problem? To the best of my knowledge it is convex for p > 1, albeit the PDE is not uniformly elliptic for p \neq 2).
Additionally, the linesearch logic has changed a bit since petsc-3.3 to make it more robust in the presence of small (in norm) current solutions and linear updates. There may still be problems with trying to "overconverge" a system where the linesearch cannot make any more progress and declares failure. See this email thread to that end: http://lists.mcs.anl.gov/pipermail/petsc-users/2012-October/015502.html It is quite possible that LU without pivoting is unstable, as John is suggesting. How big is the problem? I would suggest running a small version of the proble with -pc_type svd -pc_svd_monitor to get an idea of the extreme singular values, to see if the system is (nearly) degenerate. Dmitry. On Thu, Mar 7, 2013 at 11:33 AM, John Peterson <[email protected]> wrote: > On Thu, Mar 7, 2013 at 9:31 AM, Subramanya Gautam Sadasiva < > [email protected]> wrote: > > > Yes, that is right... my bad.. > > > > > Nevertheless, I think you are correct that there is *something* wrong with > his Jacobian. Maybe it's "good enough" to work with non-direct solvers but > fails on LU? > > -- > John > > ------------------------------------------------------------------------------ > Symantec Endpoint Protection 12 positioned as A LEADER in The Forrester > Wave(TM): Endpoint Security, Q1 2013 and "remains a good choice" in the > endpoint security space. For insight on selecting the right partner to > tackle endpoint security challenges, access the full report. > http://p.sf.net/sfu/symantec-dev2dev > _______________________________________________ > Libmesh-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/libmesh-users > ------------------------------------------------------------------------------ Symantec Endpoint Protection 12 positioned as A LEADER in The Forrester Wave(TM): Endpoint Security, Q1 2013 and "remains a good choice" in the endpoint security space. For insight on selecting the right partner to tackle endpoint security challenges, access the full report. http://p.sf.net/sfu/symantec-dev2dev _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
