# [petsc-users] strange convergence

Hoang Giang Bui hgbk2008 at gmail.com
Mon Apr 24 12:47:47 CDT 2017

Good catch. I get this for the very first step, maybe at that time the
rhs_w is zero. In the later step, it shows 2 step convergence

Residual norms for fieldsplit_u_ solve.
0 KSP Residual norm 3.165886479830e+04
1 KSP Residual norm 2.905922877684e-01
Residual norms for fieldsplit_wp_ solve.
0 KSP Residual norm 2.397669419027e-01
1 KSP Residual norm 0.000000000000e+00
0 KSP preconditioned resid norm 3.165886479920e+04 true resid norm
7.963616922323e+05 ||r(i)||/||b|| 1.000000000000e+00
Residual norms for fieldsplit_u_ solve.
0 KSP Residual norm 9.999891813771e-01
1 KSP Residual norm 1.512000395579e-05
Residual norms for fieldsplit_wp_ solve.
0 KSP Residual norm 8.192702188243e-06
1 KSP Residual norm 0.000000000000e+00
1 KSP preconditioned resid norm 5.252183822848e-02 true resid norm
7.135927677844e+04 ||r(i)||/||b|| 8.960661653427e-02
Residual norms for fieldsplit_u_ solve.
0 KSP Residual norm 6.946213936597e-01
1 KSP Residual norm 1.195514007343e-05
Residual norms for fieldsplit_wp_ solve.
0 KSP Residual norm 1.025694497535e+00
1 KSP Residual norm 0.000000000000e+00
2 KSP preconditioned resid norm 8.785709535405e-03 true resid norm
1.419341799277e+04 ||r(i)||/||b|| 1.782282866091e-02
Residual norms for fieldsplit_u_ solve.
0 KSP Residual norm 7.255149996405e-01
1 KSP Residual norm 6.583512434218e-06
Residual norms for fieldsplit_wp_ solve.
0 KSP Residual norm 1.015229700337e+00
1 KSP Residual norm 0.000000000000e+00
3 KSP preconditioned resid norm 7.110407712709e-04 true resid norm
5.284940654154e+02 ||r(i)||/||b|| 6.636357205153e-04
Residual norms for fieldsplit_u_ solve.
0 KSP Residual norm 3.512243341400e-01
1 KSP Residual norm 2.032490351200e-06
Residual norms for fieldsplit_wp_ solve.
0 KSP Residual norm 1.282327290982e+00
1 KSP Residual norm 0.000000000000e+00
4 KSP preconditioned resid norm 3.482036620521e-05 true resid norm
4.291231924307e+01 ||r(i)||/||b|| 5.388546393133e-05
Residual norms for fieldsplit_u_ solve.
0 KSP Residual norm 3.423609338053e-01
1 KSP Residual norm 4.213703301972e-07
Residual norms for fieldsplit_wp_ solve.
0 KSP Residual norm 1.157384757538e+00
1 KSP Residual norm 0.000000000000e+00
5 KSP preconditioned resid norm 1.203470314534e-06 true resid norm
4.544956156267e+00 ||r(i)||/||b|| 5.707150658550e-06
Residual norms for fieldsplit_u_ solve.
0 KSP Residual norm 3.838596289995e-01
1 KSP Residual norm 9.927864176103e-08
Residual norms for fieldsplit_wp_ solve.
0 KSP Residual norm 1.066298905618e+00
1 KSP Residual norm 0.000000000000e+00
6 KSP preconditioned resid norm 3.331619244266e-08 true resid norm
2.821511729024e+00 ||r(i)||/||b|| 3.543002829675e-06
Residual norms for fieldsplit_u_ solve.
0 KSP Residual norm 4.624964188094e-01
1 KSP Residual norm 6.418229775372e-08
Residual norms for fieldsplit_wp_ solve.
0 KSP Residual norm 9.800784311614e-01
1 KSP Residual norm 0.000000000000e+00
7 KSP preconditioned resid norm 8.788046233297e-10 true resid norm
2.849209671705e+00 ||r(i)||/||b|| 3.577783436215e-06
Linear solve converged due to CONVERGED_ATOL iterations 7

The outer operator is an explicit matrix.

Giang

On Mon, Apr 24, 2017 at 7:32 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> > On Apr 24, 2017, at 3:16 AM, Hoang Giang Bui <hgbk2008 at gmail.com> wrote:
> >
> > Thanks Barry, trying with -fieldsplit_u_type lu gives better
> convergence. I still used 4 procs though, probably with 1 proc it should
> also be the same.
> >
> > The u block used a Nitsche-type operator to connect two non-matching
> domains. I don't think it will leave some rigid body motion leads to not
> sufficient constraints. Maybe you have other idea?
> >
> >     Residual norms for fieldsplit_u_ solve.
> >     0 KSP Residual norm 3.129067184300e+05
> >     1 KSP Residual norm 5.906261468196e-01
> >     Residual norms for fieldsplit_wp_ solve.
> >     0 KSP Residual norm 0.000000000000e+00
>
>     ^^^^ something is wrong here. The sub solve should not be starting
> with a 0 residual (this means the right hand side for this sub solve is
> zero which it should not be).
>
> > FieldSplit with MULTIPLICATIVE composition: total splits = 2
>
>
>    How are you providing the outer operator? As an explicit matrix or with
> some shell matrix?
>
>
>
> >   0 KSP preconditioned resid norm 3.129067184300e+05 true resid norm
> 9.015150492169e+06 ||r(i)||/||b|| 1.000000000000e+00
> >     Residual norms for fieldsplit_u_ solve.
> >     0 KSP Residual norm 9.999955993437e-01
> >     1 KSP Residual norm 4.019774691831e-06
> >     Residual norms for fieldsplit_wp_ solve.
> >     0 KSP Residual norm 0.000000000000e+00
> >   1 KSP preconditioned resid norm 5.003913641475e-01 true resid norm
> 4.692996324114e+01 ||r(i)||/||b|| 5.205677185522e-06
> >     Residual norms for fieldsplit_u_ solve.
> >     0 KSP Residual norm 1.000012180204e+00
> >     1 KSP Residual norm 1.017367950422e-05
> >     Residual norms for fieldsplit_wp_ solve.
> >     0 KSP Residual norm 0.000000000000e+00
> >   2 KSP preconditioned resid norm 2.330910333756e-07 true resid norm
> 3.474855463983e+01 ||r(i)||/||b|| 3.854461960453e-06
> >     Residual norms for fieldsplit_u_ solve.
> >     0 KSP Residual norm 1.000004200085e+00
> >     1 KSP Residual norm 6.231613102458e-06
> >     Residual norms for fieldsplit_wp_ solve.
> >     0 KSP Residual norm 0.000000000000e+00
> >   3 KSP preconditioned resid norm 8.671259838389e-11 true resid norm
> 3.545103468011e+01 ||r(i)||/||b|| 3.932384125024e-06
> > Linear solve converged due to CONVERGED_ATOL iterations 3
> > KSP Object: 4 MPI processes
> >   type: gmres
> >     GMRES: restart=1000, using Modified Gram-Schmidt Orthogonalization
> >     GMRES: happy breakdown tolerance 1e-30
> >   maximum iterations=1000, initial guess is zero
> >   tolerances:  relative=1e-20, absolute=1e-09, divergence=10000
> >   left preconditioning
> >   using PRECONDITIONED norm type for convergence test
> > PC Object: 4 MPI processes
> >   type: fieldsplit
> >     FieldSplit with MULTIPLICATIVE composition: total splits = 2
> >     Solver info for each split is in the following KSP objects:
> >     Split number 0 Defined by IS
> >     KSP Object:    (fieldsplit_u_)     4 MPI processes
> >       type: richardson
> >         Richardson: damping factor=1
> >       maximum iterations=1, initial guess is zero
> >       tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
> >       left preconditioning
> >       using PRECONDITIONED norm type for convergence test
> >     PC Object:    (fieldsplit_u_)     4 MPI processes
> >       type: lu
> >         LU: out-of-place factorization
> >         tolerance for zero pivot 2.22045e-14
> >         matrix ordering: natural
> >         factor fill ratio given 0, needed 0
> >           Factored matrix follows:
> >             Mat Object:             4 MPI processes
> >               type: mpiaij
> >               rows=938910, cols=938910
> >               package used to perform factorization: pastix
> >               total: nonzeros=0, allocated nonzeros=0
> >       Error :                        3.36878e-14
> >           total number of mallocs used during MatSetValues calls =0
> >                 PaStiX run parameters:
> >                   Matrix type :                      Unsymmetric
> >                   Level of printing (0,1,2):         0
> >                   Number of refinements iterations : 3
> >   Error :                        3.36878e-14
> >       linear system matrix = precond matrix:
> >       Mat Object:      (fieldsplit_u_)       4 MPI processes
> >         type: mpiaij
> >         rows=938910, cols=938910, bs=3
> >   Error :                        3.36878e-14
> >   Error :                        3.36878e-14
> >         total: nonzeros=8.60906e+07, allocated nonzeros=8.60906e+07
> >         total number of mallocs used during MatSetValues calls =0
> >           using I-node (on process 0) routines: found 78749 nodes, limit
> used is 5
> >     Split number 1 Defined by IS
> >     KSP Object:    (fieldsplit_wp_)     4 MPI processes
> >       type: richardson
> >         Richardson: damping factor=1
> >       maximum iterations=1, initial guess is zero
> >       tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
> >       left preconditioning
> >       using PRECONDITIONED norm type for convergence test
> >     PC Object:    (fieldsplit_wp_)     4 MPI processes
> >       type: lu
> >         LU: out-of-place factorization
> >         tolerance for zero pivot 2.22045e-14
> >         matrix ordering: natural
> >         factor fill ratio given 0, needed 0
> >           Factored matrix follows:
> >             Mat Object:             4 MPI processes
> >               type: mpiaij
> >               rows=34141, cols=34141
> >               package used to perform factorization: pastix
> >                 Error :                        -nan
> >   Error :                        -nan
> >   Error :                        -nan
> > total: nonzeros=0, allocated nonzeros=0
> >               total number of mallocs used during MatSetValues calls =0
> >                 PaStiX run parameters:
> >                   Matrix type :                      Symmetric
> >                   Level of printing (0,1,2):         0
> >                   Number of refinements iterations : 0
> >   Error :                        -nan
> >       linear system matrix = precond matrix:
> >       Mat Object:      (fieldsplit_wp_)       4 MPI processes
> >         type: mpiaij
> >         rows=34141, cols=34141
> >         total: nonzeros=485655, allocated nonzeros=485655
> >         total number of mallocs used during MatSetValues calls =0
> >           not using I-node (on process 0) routines
> >   linear system matrix = precond matrix:
> >   Mat Object:   4 MPI processes
> >     type: mpiaij
> >     rows=973051, cols=973051
> >     total: nonzeros=9.90037e+07, allocated nonzeros=9.90037e+07
> >     total number of mallocs used during MatSetValues calls =0
> >       using I-node (on process 0) routines: found 78749 nodes, limit
> used is 5
> >
> >
> >
> > Giang
> >
> > On Sun, Apr 23, 2017 at 10:19 PM, Barry Smith <bsmith at mcs.anl.gov>
> wrote:
> >
> > > On Apr 23, 2017, at 2:42 PM, Hoang Giang Bui <hgbk2008 at gmail.com>
> wrote:
> > >
> > > Dear Matt/Barry
> > >
> > > With your options, it results in
> > >
> > >   0 KSP preconditioned resid norm 1.106709687386e+31 true resid norm
> 9.015150491938e+06 ||r(i)||/||b|| 1.000000000000e+00
> > >     Residual norms for fieldsplit_u_ solve.
> > >     0 KSP Residual norm 2.407308987203e+36
> > >     1 KSP Residual norm 5.797185652683e+72
> >
> > It looks like Matt is right, hypre is seemly producing useless garbage.
> >
> > First how do things run on one process. If you have similar problems
> then debug on one process (debugging any kind of problem is always far easy
> on one process).
> >
> > First run with -fieldsplit_u_type lu (instead of using hypre) to see if
> that works or also produces something bad.
> >
> > What is the operator and the boundary conditions for u? It could be
> singular.
> >
> >
> >
> >
> >
> >
> > >     Residual norms for fieldsplit_wp_ solve.
> > >     0 KSP Residual norm 0.000000000000e+00
> > > ...
> > > 999 KSP preconditioned resid norm 2.920157329174e+12 true resid norm
> 9.015683504616e+06 ||r(i)||/||b|| 1.000059124102e+00
> > >     Residual norms for fieldsplit_u_ solve.
> > >     0 KSP Residual norm 1.533726746719e+36
> > >     1 KSP Residual norm 3.692757392261e+72
> > >     Residual norms for fieldsplit_wp_ solve.
> > >     0 KSP Residual norm 0.000000000000e+00
> > >
> > > Do you suggest that the pastix solver for the "wp" block encounters
> small pivot? In addition, seem like the "u" block is also singular.
> > >
> > > Giang
> > >
> > > On Sun, Apr 23, 2017 at 7:39 PM, Barry Smith <bsmith at mcs.anl.gov>
> wrote:
> > >
> > >    Huge preconditioned norms but normal unpreconditioned norms almost
> always come from a very small pivot in an LU or ILU factorization.
> > >
> > >    The first thing to do is monitor the two sub solves. Run with the
> -fieldsplit_u_ksp_monitor -fieldsplit_u_ksp_max_it 1
> -fieldsplit_wp_ksp_type richardson -fieldsplit_wp_ksp_monitor
> -fieldsplit_wp_ksp_max_it 1
> > >
> > > > On Apr 23, 2017, at 12:22 PM, Hoang Giang Bui <hgbk2008 at gmail.com>
> wrote:
> > > >
> > > > Hello
> > > >
> > > > I encountered a strange convergence behavior that I have trouble to
> understand
> > > >
> > > > KSPSetFromOptions completed
> > > >   0 KSP preconditioned resid norm 1.106709687386e+31 true resid norm
> 9.015150491938e+06 ||r(i)||/||b|| 1.000000000000e+00
> > > >   1 KSP preconditioned resid norm 2.933141742664e+29 true resid norm
> 9.015152282123e+06 ||r(i)||/||b|| 1.000000198575e+00
> > > >   2 KSP preconditioned resid norm 9.686409637174e+16 true resid norm
> 9.015354521944e+06 ||r(i)||/||b|| 1.000022631902e+00
> > > >   3 KSP preconditioned resid norm 4.219243615809e+15 true resid norm
> 9.017157702420e+06 ||r(i)||/||b|| 1.000222648583e+00
> > > > .....
> > > > 999 KSP preconditioned resid norm 3.043754298076e+12 true resid norm
> 9.015425041089e+06 ||r(i)||/||b|| 1.000030454195e+00
> > > > 1000 KSP preconditioned resid norm 3.043000287819e+12 true resid
> norm 9.015424313455e+06 ||r(i)||/||b|| 1.000030373483e+00
> > > > Linear solve did not converge due to DIVERGED_ITS iterations 1000
> > > > KSP Object: 4 MPI processes
> > > >   type: gmres
> > > >     GMRES: restart=1000, using Modified Gram-Schmidt
> Orthogonalization
> > > >     GMRES: happy breakdown tolerance 1e-30
> > > >   maximum iterations=1000, initial guess is zero
> > > >   tolerances:  relative=1e-20, absolute=1e-09, divergence=10000
> > > >   left preconditioning
> > > >   using PRECONDITIONED norm type for convergence test
> > > > PC Object: 4 MPI processes
> > > >   type: fieldsplit
> > > >     FieldSplit with MULTIPLICATIVE composition: total splits = 2
> > > >     Solver info for each split is in the following KSP objects:
> > > >     Split number 0 Defined by IS
> > > >     KSP Object:    (fieldsplit_u_)     4 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:    (fieldsplit_u_)     4 MPI processes
> > > >       type: hypre
> > > >         HYPRE BoomerAMG preconditioning
> > > >         HYPRE BoomerAMG: Cycle type V
> > > >         HYPRE BoomerAMG: Maximum number of levels 25
> > > >         HYPRE BoomerAMG: Maximum number of iterations PER hypre call
> 1
> > > >         HYPRE BoomerAMG: Convergence tolerance PER hypre call 0
> > > >         HYPRE BoomerAMG: Threshold for strong coupling 0.6
> > > >         HYPRE BoomerAMG: Interpolation truncation factor 0
> > > >         HYPRE BoomerAMG: Interpolation: max elements per row 0
> > > >         HYPRE BoomerAMG: Number of levels of aggressive coarsening 0
> > > >         HYPRE BoomerAMG: Number of paths for aggressive coarsening 1
> > > >         HYPRE BoomerAMG: Maximum row sums 0.9
> > > >         HYPRE BoomerAMG: Sweeps down         1
> > > >         HYPRE BoomerAMG: Sweeps up           1
> > > >         HYPRE BoomerAMG: Sweeps on coarse    1
> > > >         HYPRE BoomerAMG: Relax down          symmetric-SOR/Jacobi
> > > >         HYPRE BoomerAMG: Relax up            symmetric-SOR/Jacobi
> > > >         HYPRE BoomerAMG: Relax on coarse     Gaussian-elimination
> > > >         HYPRE BoomerAMG: Relax weight  (all)      1
> > > >         HYPRE BoomerAMG: Outer relax weight (all) 1
> > > >         HYPRE BoomerAMG: Using CF-relaxation
> > > >         HYPRE BoomerAMG: Measure type        local
> > > >         HYPRE BoomerAMG: Coarsen type        PMIS
> > > >         HYPRE BoomerAMG: Interpolation type  classical
> > > >       linear system matrix = precond matrix:
> > > >       Mat Object:      (fieldsplit_u_)       4 MPI processes
> > > >         type: mpiaij
> > > >         rows=938910, cols=938910, bs=3
> > > >         total: nonzeros=8.60906e+07, allocated nonzeros=8.60906e+07
> > > >         total number of mallocs used during MatSetValues calls =0
> > > >           using I-node (on process 0) routines: found 78749 nodes,
> limit used is 5
> > > >     Split number 1 Defined by IS
> > > >     KSP Object:    (fieldsplit_wp_)     4 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:    (fieldsplit_wp_)     4 MPI processes
> > > >       type: lu
> > > >         LU: out-of-place factorization
> > > >         tolerance for zero pivot 2.22045e-14
> > > >         matrix ordering: natural
> > > >         factor fill ratio given 0, needed 0
> > > >           Factored matrix follows:
> > > >             Mat Object:             4 MPI processes
> > > >               type: mpiaij
> > > >               rows=34141, cols=34141
> > > >               package used to perform factorization: pastix
> > > >             Error :                        -nan
> > > >   Error :                        -nan
> > > >     total: nonzeros=0, allocated nonzeros=0
> > > >             Error :                        -nan
> > > >     total number of mallocs used during MatSetValues calls =0
> > > >                 PaStiX run parameters:
> > > >                   Matrix type :                      Symmetric
> > > >                   Level of printing (0,1,2):         0
> > > >                   Number of refinements iterations : 0
> > > >   Error :                        -nan
> > > >       linear system matrix = precond matrix:
> > > >       Mat Object:      (fieldsplit_wp_)       4 MPI processes
> > > >         type: mpiaij
> > > >         rows=34141, cols=34141
> > > >         total: nonzeros=485655, allocated nonzeros=485655
> > > >         total number of mallocs used during MatSetValues calls =0
> > > >           not using I-node (on process 0) routines
> > > >   linear system matrix = precond matrix:
> > > >   Mat Object:   4 MPI processes
> > > >     type: mpiaij
> > > >     rows=973051, cols=973051
> > > >     total: nonzeros=9.90037e+07, allocated nonzeros=9.90037e+07
> > > >     total number of mallocs used during MatSetValues calls =0
> > > >       using I-node (on process 0) routines: found 78749 nodes, limit
> used is 5
> > > >
> > > > The pattern of convergence gives a hint that this system is somehow
> bad/singular. But I don't know why the preconditioned error goes up too
> high. Anyone has an idea?
> > > >
> > > > Best regards
> > > > Giang Bui
> > > >
> > >
> > >
> >
> >
>
>
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