[petsc-users] Divergence when using Line Search

[Avery Bingham]

I have also seen this behavior, and I think this might be related to
the scaling of the variables in the nonlinear system.  I am using
PETSc through an application of MOOSE which allows for scaling of the
variables.  This scaling reduces the chance that the default cubic
backtracking line search fails, but it is not reliable on all
problems. Would it be possible to get a scaling-independent Line
Search Method implemented within PETSc?


Thanks,

Avery Bingham






*Dear Developers,

I used SNES with LS cubic and basic. In some cases the cubic model can
stabilised the global convergence BUT in some case it fails while the basic
model has given better convergence !!!

The error is as follows:
.
.
.
46:   CFL = 3894.09, Nonlinear = 6.9086e-05, Linear = (64,4.54181e-10,1e-05)
  Linear solve converged due to CONVERGED_RTOL iterations 66
47:   CFL = 3921.01, Nonlinear = 6.86117e-05, Linear =
(66,3.51905e-10,1e-05)
  Linear solve converged due to CONVERGED_RTOL iterations 64
48:   CFL = 3936.79, Nonlinear = 6.83367e-05, Linear =
(64,4.50959e-10,1e-05)
  Linear solve converged due to CONVERGED_RTOL iterations 61
[0]PETSC ERROR: --------------------- Error Message
------------------------------------
[0]PETSC ERROR: Floating point exception!
[0]PETSC ERROR: Infinite or not-a-number generated in norm!
[0]PETSC ERROR:
------------------------------------------------------------------------
[0]PETSC ERROR: Petsc Release Version 3.2.0, Patch 3, Fri Sep 30 10:28:33
CDT 2011
[0]PETSC ERROR: See docs/changes/index.html for recent updates.
[0]PETSC ERROR: See docs/faq.html for hints about trouble shooting.
[0]PETSC ERROR: See docs/index.html for manual pages.
[0]PETSC ERROR:
------------------------------------------------------------------------
[0]PETSC ERROR: ./code on a linux-gnu named baghapour by baghapour Thu Jan
5 16:44:14 2012
[0]PETSC ERROR: Libraries linked from
/home/baghapour/softs/petsc/linux-gnu-cxx-debug/lib
[0]PETSC ERROR: Configure run at Wed Nov  9 19:16:47 2011
[0]PETSC ERROR: Configure options --with-cc=gcc --with-fc=gfortran
--with-cxx=g++ --download-f2cblaslapack=1 --download-mpich=1
--with-clanguage=cxx --with-debugging=no --download-parms --download-hypre
[0]PETSC ERROR:
------------------------------------------------------------------------
[0]PETSC ERROR: VecNorm() line 167 in src/vec/vec/interface/rvector.c
[0]PETSC ERROR: SNESLineSearchCubic() line 581 in src/snes/impls/ls/ls.c
[0]PETSC ERROR: SNESSolve_LS() line 218 in src/snes/impls/ls/ls.c
[0]PETSC ERROR: SNESSolve() line 2676 in src/snes/interface/snes.c
[0]PETSC ERROR: _petsc_NewtonTimeAdvance() line 131 in Newton.cpp

I am wondering while the basic model can solve the problem but cubic model
can not.
Please help me what conditions may leads the above issue in line search.

Regards,
BehZad*
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