VecView behaviour

[Barry Smith]

    Run with GMRES, what happens?

On Jun 4, 2009, at 11:07 AM, Andreas Grassl wrote:

> Barry Smith schrieb:
>>
>> On Jun 3, 2009, at 5:29 PM, Andreas Grassl wrote:
>>
>>> Barry Smith schrieb:
>>>>
>>>> When properly running nn-cg (are you sure everything is symmetric?)
>>>> should require 10-30 iterations (certainly for model problems)
>>>
>>> ok, this was the number I expected.
>>>
>>>>
>>>>> nn-cg on 2 nodes 229 iterations, condition 6285
>>>>> nn-cg on 4 nodes 331 iterations, condition 13312
>>>>
>>>> Are you sure that your operator has the null space of only  
>>>> constants?
>>>
>>> no, I didn't touch anything regarding the null space since I thought
>>> it would be
>>> done inside the NN-preconditioner. Does this mean I have to set up a
>>> null space
>>> of the size of the Schur complement system, i.e. the number of
>>> interface DOF's?
>>
>>  No, I don't think you need to do anything about the null space. The
>> code in PETSc for NN is for (and only for) a null space of constants.
>> BTW: with 2 or 4 subdomains they all touch the boundary and likely  
>> don't
>> have a null space anyways.
>>
>> Run with -ksp_view and make sure the local solves are being done  
>> with LU
>>
>
> I don't find the anomalies... setting local_ksp-rtol to 1e-8 doesn't  
> change anything
>
> the options passed are:
>
> -is_localD_ksp_type preonly
> -is_localD_pc_factor_shift_positive_definite
> -is_localD_pc_type lu
> -is_localN_ksp_type preonly
> -is_localN_pc_factor_shift_positive_definite
> -is_localN_pc_type lu
> -ksp_rtol 1e-8
> -ksp_view
> #-is_localD_ksp_view
> #-is_localN_ksp_view
> #-nn_coarse_ksp_view
> # -pc_is_remove_nullspace_fixed this option doesn't produce any effect
> -log_summary
> -options_left
>
> and produce:
>
> -ksp_view:
>
> KSP Object:
>  type: cg
>  maximum iterations=10000
>  tolerances:  relative=1e-08, absolute=1e-50, divergence=10000
>  left preconditioning
> PC Object:
>  type: nn
>  linear system matrix = precond matrix:
>  Matrix Object:
>    type=is, rows=28632, cols=28632
>      Matrix Object:(is)
>        type=seqaij, rows=7537, cols=7537
>        total: nonzeros=359491, allocated nonzeros=602960
>          using I-node routines: found 4578 nodes, limit used is 5
>      Matrix Object:(is)
>        type=seqaij, rows=7515, cols=7515
>        total: nonzeros=349347, allocated nonzeros=601200
>          using I-node routines: found 5159 nodes, limit used is 5
>      Matrix Object:(is)
>        type=seqaij, rows=7533, cols=7533
>        total: nonzeros=357291, allocated nonzeros=602640
>          using I-node routines: found 4739 nodes, limit used is 5
>      Matrix Object:(is)
>        type=seqaij, rows=7360, cols=7360
>        total: nonzeros=364390, allocated nonzeros=588800
>          using I-node routines: found 3602 nodes, limit used is 5
>
> -is_local...:
>
> KSP Object:(is_localD_)
>  type: preonly
>  maximum iterations=10000, initial guess is zero
>  tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
>  left preconditioning
> PC Object:(is_localD_)
>  type: lu
>    LU: out-of-place factorization
>      matrix ordering: nd
>    LU: tolerance for zero pivot 1e-12
>    LU: using Manteuffel shift
>    LU: factor fill ratio needed 4.73566
>         Factored matrix follows
>        Matrix Object:
>          type=seqaij, rows=6714, cols=6714
>          package used to perform factorization: petsc
>          total: nonzeros=1479078, allocated nonzeros=1479078
>            using I-node routines: found 2790 nodes, limit used is 5
>  linear system matrix = precond matrix:
>  Matrix Object:
>    type=seqaij, rows=6714, cols=6714
>    total: nonzeros=312328, allocated nonzeros=312328
>      using I-node routines: found 4664 nodes, limit used is 5
>
> KSP Object:(is_localN_)
>  type: preonly
>  maximum iterations=10000, initial guess is zero
>  tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
>  left preconditioning
> PC Object:(is_localN_)
>  type: lu
>    LU: out-of-place factorization
>      matrix ordering: nd
>    LU: tolerance for zero pivot 1e-12
>    LU: using Manteuffel shift
>    LU: factor fill ratio needed 5.07571
>         Factored matrix follows
>        Matrix Object:
>          type=seqaij, rows=7537, cols=7537
>          package used to perform factorization: petsc
>          total: nonzeros=1824671, allocated nonzeros=1824671
>            using I-node routines: found 2939 nodes, limit used is 5
>  linear system matrix = precond matrix:
>  Matrix Object:(is)
>    type=seqaij, rows=7537, cols=7537
>    total: nonzeros=359491, allocated nonzeros=602960
>      using I-node routines: found 4578 nodes, limit used is 5
>
>
> -nn_coarse_ksp_view:
>
> KSP Object:(nn_coarse_)
>  type: preonly
>  maximum iterations=10000, initial guess is zero
>  tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
>  left preconditioning
> PC Object:(nn_coarse_)
>  type: redundant
>    Redundant preconditioner: First (color=0) of 4 PCs follows
>  KSP Object:(redundant_)
>    type: preonly
>    maximum iterations=10000, initial guess is zero
>    tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
>    left preconditioning
>  PC Object:(redundant_)
>    type: lu
>      LU: out-of-place factorization
>        matrix ordering: nd
>      LU: tolerance for zero pivot 1e-12
>      LU: factor fill ratio needed 1
>           Factored matrix follows
>          Matrix Object:
>            type=seqaij, rows=4, cols=4
>            package used to perform factorization: petsc
>            total: nonzeros=4, allocated nonzeros=4
>              not using I-node routines
>    linear system matrix = precond matrix:
>    Matrix Object:
>      type=seqaij, rows=4, cols=4
>      total: nonzeros=4, allocated nonzeros=4
>        not using I-node routines
>  linear system matrix = precond matrix:
>  Matrix Object:
>    type=mpiaij, rows=4, cols=4
>    total: nonzeros=4, allocated nonzeros=68
>      not using I-node (on process 0) routines
>
>
> cheers,
>
> ando
>
> -- 
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