[petsc-users] strange convergence
Hoang Giang Bui
hgbk2008 at gmail.com
Fri Apr 28 03:56:10 CDT 2017
It's in fact quite good
Residual norms for fieldsplit_u_ solve.
0 KSP Residual norm 4.014715925568e+00
1 KSP Residual norm 2.160497019264e-10
Residual norms for fieldsplit_wp_ solve.
0 KSP Residual norm 0.000000000000e+00
0 KSP preconditioned resid norm 4.014715925568e+00 true resid norm
9.006493082896e+06 ||r(i)||/||b|| 1.000000000000e+00
Residual norms for fieldsplit_u_ solve.
0 KSP Residual norm 9.999999999416e-01
1 KSP Residual norm 7.118380416383e-11
Residual norms for fieldsplit_wp_ solve.
0 KSP Residual norm 0.000000000000e+00
1 KSP preconditioned resid norm 1.701150951035e-10 true resid norm
5.494262251846e-04 ||r(i)||/||b|| 6.100334726599e-11
Linear solve converged due to CONVERGED_ATOL iterations 1
Giang
On Thu, Apr 27, 2017 at 5:25 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
> Run again using LU on both blocks to see what happens.
>
>
> > On Apr 27, 2017, at 2:14 AM, Hoang Giang Bui <hgbk2008 at gmail.com> wrote:
> >
> > I have changed the way to tie the nonconforming mesh. It seems the
> matrix now is better
> >
> > with -pc_type lu the output is
> > 0 KSP preconditioned resid norm 3.308678584240e-01 true resid norm
> 9.006493082896e+06 ||r(i)||/||b|| 1.000000000000e+00
> > 1 KSP preconditioned resid norm 2.004313395301e-12 true resid norm
> 2.549872332830e-05 ||r(i)||/||b|| 2.831148938173e-12
> > Linear solve converged due to CONVERGED_ATOL iterations 1
> >
> >
> > with -pc_type fieldsplit -fieldsplit_u_pc_type hypre
> -fieldsplit_wp_pc_type lu the convergence is slow
> > 0 KSP preconditioned resid norm 1.116302362553e-01 true resid norm
> 9.006493083520e+06 ||r(i)||/||b|| 1.000000000000e+00
> > 1 KSP preconditioned resid norm 2.582134825666e-02 true resid norm
> 9.268347719866e+06 ||r(i)||/||b|| 1.029073984060e+00
> > ...
> > 824 KSP preconditioned resid norm 1.018542387738e-09 true resid norm
> 2.906608839310e+02 ||r(i)||/||b|| 3.227237074804e-05
> > 825 KSP preconditioned resid norm 9.743727947637e-10 true resid norm
> 2.820369993061e+02 ||r(i)||/||b|| 3.131485215062e-05
> > Linear solve converged due to CONVERGED_ATOL iterations 825
> >
> > checking with additional -fieldsplit_u_ksp_type richardson
> -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 gives
> >
> > 0 KSP preconditioned resid norm 1.116302362553e-01 true resid norm
> 9.006493083520e+06 ||r(i)||/||b|| 1.000000000000e+00
> > Residual norms for fieldsplit_u_ solve.
> > 0 KSP Residual norm 5.803507549280e-01
> > 1 KSP Residual norm 2.069538175950e-01
> > Residual norms for fieldsplit_wp_ solve.
> > 0 KSP Residual norm 0.000000000000e+00
> > 1 KSP preconditioned resid norm 2.582134825666e-02 true resid norm
> 9.268347719866e+06 ||r(i)||/||b|| 1.029073984060e+00
> > Residual norms for fieldsplit_u_ solve.
> > 0 KSP Residual norm 7.831796195225e-01
> > 1 KSP Residual norm 1.734608520110e-01
> > Residual norms for fieldsplit_wp_ solve.
> > 0 KSP Residual norm 0.000000000000e+00
> > ....
> > 823 KSP preconditioned resid norm 1.065070135605e-09 true resid norm
> 3.081881356833e+02 ||r(i)||/||b|| 3.421843916665e-05
> > Residual norms for fieldsplit_u_ solve.
> > 0 KSP Residual norm 6.113806394327e-01
> > 1 KSP Residual norm 1.535465290944e-01
> > Residual norms for fieldsplit_wp_ solve.
> > 0 KSP Residual norm 0.000000000000e+00
> > 824 KSP preconditioned resid norm 1.018542387746e-09 true resid norm
> 2.906608839353e+02 ||r(i)||/||b|| 3.227237074851e-05
> > Residual norms for fieldsplit_u_ solve.
> > 0 KSP Residual norm 6.123437055586e-01
> > 1 KSP Residual norm 1.524661826133e-01
> > Residual norms for fieldsplit_wp_ solve.
> > 0 KSP Residual norm 0.000000000000e+00
> > 825 KSP preconditioned resid norm 9.743727947718e-10 true resid norm
> 2.820369990571e+02 ||r(i)||/||b|| 3.131485212298e-05
> > Linear solve converged due to CONVERGED_ATOL iterations 825
> >
> >
> > The residual for wp block is zero since in this first step the rhs is
> zero. As can see in the output, the multigrid does not perform well to
> reduce the residual in the sub-solve. Is my observation right? what can be
> done to improve this?
> >
> >
> > Giang
> >
> > On Tue, Apr 25, 2017 at 12:17 AM, Barry Smith <bsmith at mcs.anl.gov>
> wrote:
> >
> > This can happen in the matrix is singular or nearly singular or if
> the factorization generates small pivots, which can occur for even
> nonsingular problems if the matrix is poorly scaled or just plain nasty.
> >
> >
> > > On Apr 24, 2017, at 5:10 PM, Hoang Giang Bui <hgbk2008 at gmail.com>
> wrote:
> > >
> > > It took a while, here I send you the output
> > >
> > > 0 KSP preconditioned resid norm 3.129073545457e+05 true resid norm
> 9.015150492169e+06 ||r(i)||/||b|| 1.000000000000e+00
> > > 1 KSP preconditioned resid norm 7.442444222843e-01 true resid norm
> 1.003356247696e+02 ||r(i)||/||b|| 1.112966720375e-05
> > > 2 KSP preconditioned resid norm 3.267453132529e-07 true resid norm
> 3.216722968300e+01 ||r(i)||/||b|| 3.568130084011e-06
> > > 3 KSP preconditioned resid norm 1.155046883816e-11 true resid norm
> 3.234460376820e+01 ||r(i)||/||b|| 3.587805194854e-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: 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=973051, cols=973051
> > > package used to perform factorization: pastix
> > > Error : 3.24786e-14
> > > total: nonzeros=0, allocated nonzeros=0
> > > 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 : 3.24786e-14
> > > linear system matrix = precond matrix:
> > > Mat Object: 4 MPI processes
> > > type: mpiaij
> > > rows=973051, cols=973051
> > > Error : 3.24786e-14
> > > 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
> > > Error : 3.24786e-14
> > >
> > > It doesn't do as you said. Something is not right here. I will look in
> depth.
> > >
> > > Giang
> > >
> > > On Mon, Apr 24, 2017 at 8:21 PM, Barry Smith <bsmith at mcs.anl.gov>
> wrote:
> > >
> > > > On Apr 24, 2017, at 12:47 PM, Hoang Giang Bui <hgbk2008 at gmail.com>
> wrote:
> > > >
> > > > Good catch. I get this for the very first step, maybe at that time
> the rhs_w is zero.
> > >
> > > With the multiplicative composition the right hand side of the
> second solve is the initial right hand side of the second solve minus
> A_10*x where x is the solution to the first sub solve and A_10 is the lower
> left block of the outer matrix. So unless both the initial right hand side
> has a zero for the second block and A_10 is identically zero the right hand
> side for the second sub solve should not be zero. Is A_10 == 0?
> > >
> > >
> > > > 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
> > >
> > > The outer residual norms are still wonky, the preconditioned
> residual norm goes from 3.165886479920e+04 to 5.252183822848e-02 which is a
> huge drop but the 7.963616922323e+05 drops very much less
> 7.135927677844e+04. This is not normal.
> > >
> > > What if you just use -pc_type lu for the entire system (no
> fieldsplit), does the true residual drop to almost zero in the first
> iteration (as it should?). Send the output.
> > >
> > >
> > >
> > > > 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 additional options -fieldsplit_u_ksp_type richardson
> -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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