[petsc-users] GAMG Indefinite

[Mark Adams]

Barry, this is probably the Chebyshev problem.

Sanjay, this is fixed but has not yet been moved to the master branch.  You
can fix this now with with -ksp_chebyshev_esteig_random.  This should
recover v3.5 semantics.

Mark

On Thu, May 19, 2016 at 2:42 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>    We see this occasionally, there is nothing in the definition of GAMG
> that guarantees a positive definite preconditioner even if the operator was
> positive definite so we don't think this is a bug in the code. We've found
> using a slightly stronger smoother, like one more smoothing step seems to
> remove the problem.
>
>    Barry
>
> > On May 19, 2016, at 1:07 PM, Sanjay Govindjee <s_g at berkeley.edu> wrote:
> >
> > I am trying to solve a very ordinary nonlinear elasticity problem
> > using -ksp_type cg -pc_type gamg in PETSc 3.7.0, which worked fine
> > in PETSc 3.5.3.
> >
> > The problem I am seeing is on my first Newton iteration, the Ax=b
> > solve returns with and Indefinite Preconditioner error
> (KSPGetConvergedReason == -8):
> > (log_view.txt output also attached)
> >
> >   0 KSP Residual norm 8.411630828687e-02
> >   1 KSP Residual norm 2.852209578900e-02
> >   NO CONVERGENCE REASON:  Indefinite Preconditioner
> >   NO CONVERGENCE REASON:  Indefinite Preconditioner
> >
> > On the next and subsequent Newton iterations, I see perfectly normal
> > behavior and the problem converges quadratically.  The results look fine.
> >
> > I tried the same problem with -pc_type jacobi as well as super-lu, and
> mumps
> > and they all work without complaint.
> >
> > My run line for GAMG is:
> > -ksp_type cg -ksp_monitor -log_view -pc_type gamg -pc_gamg_type agg
> -pc_gamg_agg_nsmooths 1 -options_left
> >
> > The code flow looks like:
> >
> > ! If no matrix allocation yet
> > if(Kmat.eq.0) then
> >   call MatCreate(PETSC_COMM_WORLD,Kmat,ierr)
> >   call
> MatSetSizes(Kmat,numpeq,numpeq,PETSC_DETERMINE,PETSC_DETERMINE,ierr)
> >   call MatSetBlockSize(Kmat,nsbk,ierr)
> >   call MatSetFromOptions(Kmat, ierr)
> >   call MatSetType(Kmat,MATAIJ,ierr)
> >   call
> MatMPIAIJSetPreallocation(Kmat,PETSC_NULL_INTEGER,mr(np(246)),PETSC_NULL_INTEGER,mr(np(247)),ierr)
> >   call
> MatSeqAIJSetPreallocation(Kmat,PETSC_NULL_INTEGER,mr(np(246)),ierr)
> > endif
> >
> > call MatZeroEntries(Kmat,ierr)
> >
> > ! Code to set values in matrix
> >
> > call MatAssemblyBegin(Kmat, MAT_FINAL_ASSEMBLY, ierr)
> > call MatAssemblyEnd(Kmat, MAT_FINAL_ASSEMBLY, ierr)
> > call MatSetOption(Kmat,MAT_NEW_NONZERO_LOCATIONS,PETSC_TRUE,ierr)
> >
> > ! If no rhs allocation yet
> > if(rhs.eq.0) then
> >   call VecCreate        (PETSC_COMM_WORLD, rhs, ierr)
> >   call VecSetSizes      (rhs, numpeq, PETSC_DECIDE, ierr)
> >   call VecSetFromOptions(rhs, ierr)
> > endif
> >
> > ! Code to set values in RHS
> >
> > call VecAssemblyBegin(rhs, ierr)
> > call VecAssemblyEnd(rhs, ierr)
> >
> > if(kspsol_exists) then
> >   call KSPDestroy(kspsol,ierr)
> > endif
> >
> > call KSPCreate(PETSC_COMM_WORLD, kspsol   ,ierr)
> > call KSPSetOperators(kspsol, Kmat, Kmat, ierr)
> > call KSPSetFromOptions(kspsol,ierr)
> > call KSPGetPC(kspsol, pc ,      ierr)
> >
> > call PCSetCoordinates(pc,ndm,numpn,hr(np(43)),ierr)
> >
> > call KSPSolve(kspsol, rhs, sol, ierr)
> > call KSPGetConvergedReason(kspsol,reason,ierr)
> >
> > ! update solution, go back to the top
> >
> > reason is coming back as -8 on my first Ax=b solve and 2 or 3 after that
> > (with gamg).  With the other solvers it is coming back as 2 or 3 for
> > iterative options and 4 if I use one of the direct solvers.
> >
> > Any ideas on what is causing the Indefinite PC on the first iteration
> with GAMG?
> >
> > Thanks in advance,
> > -sanjay
> >
> > --
> > -----------------------------------------------
> > Sanjay Govindjee, PhD, PE
> > Professor of Civil Engineering
> >
> > 779 Davis Hall
> > University of California
> > Berkeley, CA 94720-1710
> >
> > Voice:  +1 510 642 6060
> > FAX:    +1 510 643 5264
> >
> > s_g at berkeley.edu
> > http://www.ce.berkeley.edu/~sanjay
> >
> > -----------------------------------------------
> >
> > Books:
> >
> > Engineering Mechanics of Deformable
> > Solids: A Presentation with Exercises
> >
> >
> http://www.oup.com/us/catalog/general/subject/Physics/MaterialsScience/?view=usa&ci=9780199651641
> > http://ukcatalogue.oup.com/product/9780199651641.do
> > http://amzn.com/0199651647
> >
> >
> > Engineering Mechanics 3 (Dynamics) 2nd Edition
> >
> > http://www.springer.com/978-3-642-53711-0
> > http://amzn.com/3642537111
> >
> >
> > Engineering Mechanics 3, Supplementary Problems: Dynamics
> >
> > http://www.amzn.com/B00SOXN8JU
> >
> >
> > -----------------------------------------------
> >
> > <log_view.txt>
>
>
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