[petsc-users] Petsc ILU PC Change between 3.6.4 and 3.7.x?

[Barry Smith]

   Thanks for confirming this. The change was actually in the 3.4 release. I have updated the 3.4 changes file to include this change in both the maint and master branches.

    Barry

> On Aug 11, 2017, at 12:47 PM, Gaetan Kenway <gaetank at gmail.com> wrote:
> 
> OK, so that was certainly it.  I vaguely recall reading something about this on the mailing list at one point in time, but couldn't find anything. 
> I would definitely put something on the 3.7 change doc since I looked there first to see if anything stuck out. 
> 
> Thanks!
> 
> On Fri, Aug 11, 2017 at 10:28 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
>    Run with the additional option
> 
>  -sub_pc_factor_shift_type nonzero
> 
> does this resolve the problem. We changed the default behavior for ILU when it detects "zero" pivots.
> 
> Please let us know if this resolves the problem and we'll update the changes file.
> 
>    Barry
> 
> 
> 
> > On Aug 11, 2017, at 12:14 PM, Gaetan Kenway <gaetank at gmail.com> wrote:
> >
> > Hi All
> >
> > I'm in the process of updating a code that uses PETSc for solving linear systems for an unstructured CFD code. As of recently, it was using an ancient version (3.3). However, when I updated it up to 3.7.6 I ended up running into issues with one of the KSP solves. The remainder of the code is identical,
> > I've tracked the issue down to occurring between version 3.6.4 and version 3.7.0 . The same issue is present on the most recent version 3.7.6.
> >
> > Specifically the issue is that on the second iteration, on the 3.7 version the KSP kicks out with KSP converged reason of -11 or  KSP_DIVERGED_PCSETUP_FAILED . After that the two runs differ.  The KSPView for each of the two are given below which are identical, up to small formatting changes. There is still more I can track down, but I thought I would ask if someone knows what might have changed between these two versions which could save me a lot of time.
> >
> > Thanks,
> > Gaetan
> >
> > 3.6 KSP View:
> > KSP Object: 8 MPI processes
> >   type: gmres
> >     GMRES: restart=3, using Classical (unmodified) Gram-Schmidt Orthogonalization with no iterative refinement
> >     GMRES: happy breakdown tolerance 1e-30
> >   maximum iterations=3
> >   using preconditioner applied to right hand side for initial guess
> >   tolerances:  relative=1e-08, absolute=1e-20, divergence=1e+15
> >   left preconditioning
> >   using nonzero initial guess
> >   using PRECONDITIONED norm type for convergence test
> > PC Object: 8 MPI processes
> >   type: bjacobi
> >     block Jacobi: number of blocks = 8
> >     Local solve is same for all blocks, in the following KSP and PC objects:
> >   KSP Object:  (sub_)   1 MPI processes
> >     type: preonly
> >     maximum iterations=10000, initial guess is zero
> >     tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
> >     left preconditioning
> >     using NONE norm type for convergence test
> >   PC Object:  (sub_)   1 MPI processes
> >     type: ilu
> >       ILU: out-of-place factorization
> >       0 levels of fill
> >       tolerance for zero pivot 2.22045e-14
> >       matrix ordering: natural
> >       factor fill ratio given 1, needed 1
> >         Factored matrix follows:
> >           Mat Object:           1 MPI processes
> >             type: seqaij
> >             rows=46439, cols=46439
> >             package used to perform factorization: petsc
> >             total: nonzeros=502615, allocated nonzeros=502615
> >             total number of mallocs used during MatSetValues calls =0
> >               not using I-node routines
> >     linear system matrix = precond matrix:
> >     Mat Object:     1 MPI processes
> >       type: seqaij
> >       rows=46439, cols=46439
> >       total: nonzeros=502615, allocated nonzeros=504081
> >       total number of mallocs used during MatSetValues calls =0
> >         not using I-node routines
> >   linear system matrix = precond matrix:
> >   Mat Object:   8 MPI processes
> >     type: mpiaij
> >     rows=368656, cols=368656
> >     total: nonzeros=4.63682e+06, allocated nonzeros=4.64417e+06
> >     total number of mallocs used during MatSetValues calls =0
> >       not using I-node (on process 0) routines
> > <my output: reason, iterations, rtol, atol>
> > reason,its: 2 3 0.001 1e-20
> >
> >
> > Petsc 3.7 KSP View
> > KSP Object: 8 MPI processes
> >   type: gmres
> >     GMRES: restart=3, using Classical (unmodified) Gram-Schmidt Orthogonalization with no iterative refinement
> >     GMRES: happy breakdown tolerance 1e-30
> >   maximum iterations=3
> >   using preconditioner applied to right hand side for initial guess
> >   tolerances:  relative=1e-08, absolute=1e-20, divergence=1e+15
> >   left preconditioning
> >   using nonzero initial guess
> >   using PRECONDITIONED norm type for convergence test
> > PC Object: 8 MPI processes
> >   type: bjacobi
> >     block Jacobi: number of blocks = 8
> >     Local solve is same for all blocks, in the following KSP and PC objects:
> >   KSP Object:  (sub_)   1 MPI processes
> >     type: preonly
> >     maximum iterations=10000, initial guess is zero
> >     tolerances:  relative=1e-05, absolute=1e-50, divergence=10000.
> >     left preconditioning
> >     using NONE norm type for convergence test
> >   PC Object:  (sub_)   1 MPI processes
> >     type: ilu
> >       ILU: out-of-place factorization
> >       0 levels of fill
> >       tolerance for zero pivot 2.22045e-14
> >       matrix ordering: natural
> >       factor fill ratio given 1., needed 1.
> >         Factored matrix follows:
> >           Mat Object:           1 MPI processes
> >             type: seqaij
> >             rows=46439, cols=46439
> >             package used to perform factorization: petsc
> >             total: nonzeros=502615, allocated nonzeros=502615
> >             total number of mallocs used during MatSetValues calls =0
> >               not using I-node routines
> >     linear system matrix = precond matrix:
> >     Mat Object:     1 MPI processes
> >       type: seqaij
> >       rows=46439, cols=46439
> >       total: nonzeros=502615, allocated nonzeros=504081
> >       total number of mallocs used during MatSetValues calls =0
> >         not using I-node routines
> >   linear system matrix = precond matrix:
> >   Mat Object:   8 MPI processes
> >     type: mpiaij
> >     rows=368656, cols=368656
> >     total: nonzeros=4636822, allocated nonzeros=4644168
> >     total number of mallocs used during MatSetValues calls =0
> >       not using I-node (on process 0) routines
> > <my output: reason, iterations, rtol, atol>
> > reason,its: -11 0 0.001 1e-20
> >
> >
> 
>