[petsc-dev] Using PCFieldSplitSetIS

Wed Mar 16 11:03:46 CDT 2011

On Mar 16, 2011, at 8:57 AM, Thomas Witkowski wrote:

-pc_fieldsplit_type schur -fieldsplit_interior_ksp_type preonly -fieldsplit_interior_pc_type bjacobi -fieldsplit_interior_sub_pc_type lu -fieldsplit_boundary_ksp_monitor -ksp_monitor_true_residual 

>   Residual norms for fieldsplit_boundary_ solve.
>   0 KSP Residual norm 1.790059331071e-04
>  .....
>  18 KSP Residual norm 1.593454221996e-09
> 0 KSP preconditioned resid norm 5.745043818120e-01 true resid norm 1.584249437360e-01 ||r(i)||/||b|| 1.000000000000e+00  
        This is the norms on the outer iteration variables
>   Residual norms for fieldsplit_boundary_ solve.
>   0 KSP Residual norm 1.790059331000e-04
        This is the norms on the Schur complement iteration
>  ....
>  18 KSP Residual norm 1.593449602302e-09

    It is unclear to me why it starts up another solve here, starting basically where it left off. I think it should just kick out to print the norm of the residual of the outer iteration.

>   Residual norms for fieldsplit_boundary_ solve.
>   0 KSP Residual norm 1.593449603155e-09
>  ...
>  18 KSP Residual norm 1.335744434252e-14
> 1 KSP preconditioned resid norm 2.608069232839e-13 true resid norm 1.449869994655e-13 ||r(i)||/||b|| 9.151778504469e-13
> 

 Are you running with petsc-dev?

Please run with -ksp_view and send the output.

When I run tutorials/multiphysics/mp.c with the options ./mp -couple -snes_monitor_short -pc_type fieldsplit -ksp_monitor -pc_fieldsplit_type schur -fieldsplit_ksp_monitor -fieldsplit_1_ksp_type fgmres -fieldsplit_0_ksp_type gmres   -snes_view I do not see the "double" iteration business. 

   Barry

> 
> So, are there now two or one outer iterations?
> 
> Thomas
> 
> 
> 
> 
> Matthew Knepley wrote:
>> On Wed, Mar 16, 2011 at 8:27 AM, Thomas Witkowski <thomas.witkowski at tu-dresden.de <mailto:thomas.witkowski at tu-dresden.de>> wrote:
>> 
>>    Jed Brown wrote:
>> 
>>        On Wed, Mar 16, 2011 at 07:37, Thomas Witkowski
>>        <thomas.witkowski at tu-dresden.de
>>        <mailto:thomas.witkowski at tu-dresden.de>
>>        <mailto:thomas.witkowski at tu-dresden.de
>>        <mailto:thomas.witkowski at tu-dresden.de>>> wrote:
>> 
>>           Thanks for explanations! It works fine in my code. But I
>>        have two
>>           questions about it, maybe you can help me with them:
>>           - To the first, is the LU factorization on block A_00 done
>>        only once?
>> 
>> 
>>        Yes, one way to confirm this is to run with -log_summary and
>>        check MatLUFactor{Sym,Num}.
>>                    - I have run the code with -fieldsplit_1_ksp_monitor to get
>>        some
>>           more information about the internal solves. I expected to get
>>           information about one iterative solver (for solving the Schur
>>           complement system), but I got three, all of them need around 20
>>           iterations for my example. Could you explain to me what is
>>           actually solved there?
>> 
>> 
>>        I'm going to guess that you still have an outer KSP that (in
>>        the global norm, rather than the partitioned norm used inside
>>        of splits) has a tighter tolerance, therefore it takes a few
>>        outer iterations. If you use loose inner tolerances then the
>>        preconditioner becomes nonlinear and you'll need to use FGMRES
>>        for the outer. When in doubt, run with -ksp_view and show us
>>        the results if you don't understand. Additionally, monitoring
>>        inner solves separately can be useful, e.g.
>>        -fieldsplit_0_ksp_converged_reason -fieldsplit_1_ksp_monitor
>>        -ksp_monitor_true_residual.
>> 
>>    Okay, I run my code with the options "-pc_fieldsplit_type schur
>>    -fieldsplit_interior_ksp_type preonly -fieldsplit_interior_pc_type
>>    bjacobi -fieldsplit_interior_sub_pc_type lu
>>    -fieldsplit_boundary_ksp_monitor -ksp_monitor_true_residual
>>    -fieldsplit_interior_ksp_converged_reason". The splits are named
>>    "interior" and "boundary". The ksp output is as follows:
>> 
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      Residual norms for fieldsplit_boundary_ solve.
>>      0 KSP Residual norm 1.790059331071e-04
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      1 KSP Residual norm 1.237356212928e-04
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      2 KSP Residual norm 7.952220245101e-05
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      3 KSP Residual norm 3.502858665398e-05
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      4 KSP Residual norm 1.601085190129e-05
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      5 KSP Residual norm 8.491161243057e-06
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      6 KSP Residual norm 4.778227395989e-06
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      7 KSP Residual norm 2.571919352633e-06
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      8 KSP Residual norm 1.353979940120e-06
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      9 KSP Residual norm 7.408377337496e-07
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     10 KSP Residual norm 3.810694345834e-07
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     11 KSP Residual norm 1.955889542056e-07
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     12 KSP Residual norm 9.938906113920e-08
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     13 KSP Residual norm 4.893445675773e-08
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     14 KSP Residual norm 2.395128458062e-08
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     15 KSP Residual norm 1.2464425896 <tel:1.2464425896>57e-08
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     16 KSP Residual norm 6.316454504022e-09
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     17 KSP Residual norm 3.088668836241e-09
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     18 KSP Residual norm 1.593454221996e-09
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>    [0]  Petsc-Iteration 0: 0.574504
>>     0 KSP preconditioned resid norm 5.745043818120e-01 true resid
>>    norm 1.584249437360e-01 ||r(i)||/||b|| 1.000000000000e+00
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      Residual norms for fieldsplit_boundary_ solve.
>>      0 KSP Residual norm 1.790059331000e-04
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      1 KSP Residual norm 1.237356237744e-04
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      2 KSP Residual norm 7.952220078415e-05
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      3 KSP Residual norm 3.502859285561e-05
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      4 KSP Residual norm 1.601086485810e-05
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      5 KSP Residual norm 8.491169384185e-06
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      6 KSP Residual norm 4.778229157872e-06
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      7 KSP Residual norm 2.571917112191e-06
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      8 KSP Residual norm 1.353977280183e-06
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      9 KSP Residual norm 7.408352317360e-07
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     10 KSP Residual norm 3.810710583336e-07
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     11 KSP Residual norm 1.955898169394e-07
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     12 KSP Residual norm 9.938892788465e-08
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     13 KSP Residual norm 4.893428546840e-08
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     14 KSP Residual norm 2.395120857135e-08
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     15 KSP Residual norm 1.2464367927 <tel:1.2464367927>84e-08
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     16 KSP Residual norm 6.316409779118e-09
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     17 KSP Residual norm 3.088649355374e-09
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     18 KSP Residual norm 1.593449602302e-09
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      Residual norms for fieldsplit_boundary_ solve.
>>      0 KSP Residual norm 1.593449603155e-09
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      1 KSP Residual norm 1.011857676662e-09
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      2 KSP Residual norm 5.660892669788e-10
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      3 KSP Residual norm 3.046799343903e-10
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      4 KSP Residual norm 1.6004713993 <tel:1.6004713993>29e-10
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      5 KSP Residual norm 8.083216601016e-11
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      6 KSP Residual norm 4.308671648345e-11
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      7 KSP Residual norm 2.381959817139e-11
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      8 KSP Residual norm 1.264839790114e-11
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>      9 KSP Residual norm 6.435098853282e-12
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     10 KSP Residual norm 3.184769579797e-12
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     11 KSP Residual norm 1.5022019430 <tel:1.5022019430>16e-12
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     12 KSP Residual norm 7.099486208425e-13
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     13 KSP Residual norm 3.443222176388e-13
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     14 KSP Residual norm 1.6478434989 <tel:1.6478434989>12e-13
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     15 KSP Residual norm 8.208508173926e-14
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     16 KSP Residual norm 4.376604355287e-14
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     17 KSP Residual norm 2.596069152755e-14
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     18 KSP Residual norm 1.335744434252e-14
>>      Linear solve converged due to CONVERGED_ITS iterations 1
>>     1 KSP preconditioned resid norm 2.608069232839e-13 true resid
>>    norm 1.449869994655e-13 ||r(i)||/||b|| 9.151778504469e-13
>> 
>>    I have no idea how to interpret this output! Could you help me
>>    with it?
>> 
>> 
>> Get rid of -fieldsplit_interior_ksp_converged_reason. It is confusing things. Then you will see
>> the outer iteration and the inner boundary iteration which is indented.
>> 
>>   Matt
>> 
>> 
>>    Thomas
>> 
>> 
>> 
>> 
>> -- 
>> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
>> -- Norbert Wiener
> 