[petsc-dev] Using PCFieldSplitSetIS
Thomas Witkowski
thomas.witkowski at tu-dresden.de
Wed Mar 16 09:27:41 CDT 2011
Matthew Knepley wrote:
> On Wed, Mar 16, 2011 at 8:57 AM, Thomas Witkowski
> <thomas.witkowski at tu-dresden.de
> <mailto:thomas.witkowski at tu-dresden.de>> wrote:
>
> Matt, it makes the output nicer, but does not help me to
> understand what's going on inside of PETSc:
>
>
> Residual norms for fieldsplit_boundary_ solve.
> 0 KSP Residual norm 1.790059331071e-04
> 1 KSP Residual norm 1.237356212928e-04
> 2 KSP Residual norm 7.952220245101e-05
> 3 KSP Residual norm 3.502858665398e-05
> 4 KSP Residual norm 1.601085190129e-05
> 5 KSP Residual norm 8.491161243057e-06
> 6 KSP Residual norm 4.778227395989e-06
> 7 KSP Residual norm 2.571919352633e-06
> 8 KSP Residual norm 1.353979940120e-06
> 9 KSP Residual norm 7.408377337496e-07
> 10 KSP Residual norm 3.810694345834e-07
> 11 KSP Residual norm 1.955889542056e-07
> 12 KSP Residual norm 9.938906113920e-08
> 13 KSP Residual norm 4.893445675773e-08
> 14 KSP Residual norm 2.395128458062e-08
> 15 KSP Residual norm 1.2464425896 <tel:1.2464425896>57e-08
> 16 KSP Residual norm 6.316454504022e-09
> 17 KSP Residual norm 3.088668836241e-09
> 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
> Residual norms for fieldsplit_boundary_ solve.
> 0 KSP Residual norm 1.790059331000e-04
> 1 KSP Residual norm 1.237356237744e-04
> 2 KSP Residual norm 7.952220078415e-05
> 3 KSP Residual norm 3.502859285561e-05
> 4 KSP Residual norm 1.601086485810e-05
> 5 KSP Residual norm 8.491169384185e-06
> 6 KSP Residual norm 4.778229157872e-06
> 7 KSP Residual norm 2.571917112191e-06
> 8 KSP Residual norm 1.353977280183e-06
> 9 KSP Residual norm 7.408352317360e-07
> 10 KSP Residual norm 3.810710583336e-07
> 11 KSP Residual norm 1.955898169394e-07
> 12 KSP Residual norm 9.938892788465e-08
> 13 KSP Residual norm 4.893428546840e-08
> 14 KSP Residual norm 2.395120857135e-08
> 15 KSP Residual norm 1.2464367927 <tel:1.2464367927>84e-08
> 16 KSP Residual norm 6.316409779118e-09
> 17 KSP Residual norm 3.088649355374e-09
> 18 KSP Residual norm 1.593449602302e-09
> Residual norms for fieldsplit_boundary_ solve.
> 0 KSP Residual norm 1.593449603155e-09
> 1 KSP Residual norm 1.011857676662e-09
> 2 KSP Residual norm 5.660892669788e-10
> 3 KSP Residual norm 3.046799343903e-10
> 4 KSP Residual norm 1.6004713993 <tel:1.6004713993>29e-10
> 5 KSP Residual norm 8.083216601016e-11
> 6 KSP Residual norm 4.308671648345e-11
> 7 KSP Residual norm 2.381959817139e-11
> 8 KSP Residual norm 1.264839790114e-11
> 9 KSP Residual norm 6.435098853282e-12
> 10 KSP Residual norm 3.184769579797e-12
> 11 KSP Residual norm 1.5022019430 <tel:1.5022019430>16e-12
> 12 KSP Residual norm 7.099486208425e-13
> 13 KSP Residual norm 3.443222176388e-13
> 14 KSP Residual norm 1.6478434989 <tel:1.6478434989>12e-13
> 15 KSP Residual norm 8.208508173926e-14
> 16 KSP Residual norm 4.376604355287e-14
> 17 KSP Residual norm 2.596069152755e-14
> 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
>
>
> So, are there now two or one outer iterations?
>
>
> 1 outer (NOT INDENTED) which took two iterates. 1 inner (INDENTED)
> which ran 3 times.
Mh, I've some problems to understand the whole situation, so sorry for
recurrent questions. Why does the "Schur fieldsplit solver" needs two
iterations? I thought that if the A_00 block is directly factorized and
the Schur system is solved accurately than whole system should be solved
within one iteration. And why does the first iteration make on solve of
fieldsplit_boundary_ solve, but the second iteration runs this two times?
Thomas
>
> Matt
>
>
> 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>
> <mailto: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>>
> <mailto: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>
> <tel: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>
> <tel: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>
> <tel: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>
> <tel: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>
> <tel: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
>
>
>
>
>
> --
> 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
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