[petsc-users] Understanding inner vs outer fieldsplit convergence

[David Knezevic]

I'm exploring fieldsplit with Schur (this continues from some emails I sent
a few weeks ago about this topic), and I had a quick question about the
inner vs outer convergence.

I've pasted the output below from "-ksp_monitor
-fieldsplit_FE_split_ksp_monitor", and I'm just wondering about why the
second outer iteration has two inner iteration loops, whereas all the other
outer iterations have one inner iteration loop? I assume it is something to
do with a convergence tolerance, but it's not clear to me which tolerance
would control that.

Thanks,
David

------------------------------------------------------------------

    Residual norms for fieldsplit_FE_split_ solve.
    0 KSP Residual norm 4.742303891408e+01
    1 KSP Residual norm 2.909253505630e-01
    2 KSP Residual norm 9.891933795059e-02
    3 KSP Residual norm 7.147789520745e-02
    4 KSP Residual norm 1.668752967907e-02
    5 KSP Residual norm 5.019869896662e-03
    6 KSP Residual norm 2.848579237244e-03
    7 KSP Residual norm 2.847897269641e-03
    8 KSP Residual norm 2.840502392022e-03
    9 KSP Residual norm 2.831875522381e-03
   10 KSP Residual norm 2.688309287993e-03
   11 KSP Residual norm 1.351494303229e-03
   12 KSP Residual norm 1.350874246297e-03
   13 KSP Residual norm 9.154691604943e-06
  0 KSP Residual norm 2.254632353893e+02
    Residual norms for fieldsplit_FE_split_ solve.
    0 KSP Residual norm 4.742303891408e+01
    1 KSP Residual norm 2.909253505630e-01
    2 KSP Residual norm 9.891933795059e-02
    3 KSP Residual norm 7.147789520745e-02
    4 KSP Residual norm 1.668752967907e-02
    5 KSP Residual norm 5.019869896662e-03
    6 KSP Residual norm 2.848579237244e-03
    7 KSP Residual norm 2.847897269641e-03
    8 KSP Residual norm 2.840502392022e-03
    9 KSP Residual norm 2.831875522381e-03
   10 KSP Residual norm 2.688309287993e-03
   11 KSP Residual norm 1.351494303229e-03
   12 KSP Residual norm 1.350874246297e-03
   13 KSP Residual norm 9.154691604943e-06
    Residual norms for fieldsplit_FE_split_ solve.
    0 KSP Residual norm 1.554697370480e-05
    1 KSP Residual norm 1.554471967929e-05
    2 KSP Residual norm 1.551293889691e-05
    3 KSP Residual norm 8.031337431574e-06
    4 KSP Residual norm 4.137185786243e-06
    5 KSP Residual norm 4.066606123330e-06
    6 KSP Residual norm 4.051107282928e-06
    7 KSP Residual norm 4.047442850256e-06
    8 KSP Residual norm 4.047129984657e-06
    9 KSP Residual norm 4.030697964677e-06
   10 KSP Residual norm 2.882383190940e-06
   11 KSP Residual norm 3.325005138484e-07
   12 KSP Residual norm 2.107354774516e-07
   13 KSP Residual norm 2.107005548204e-07
   14 KSP Residual norm 4.399320792736e-08
   15 KSP Residual norm 4.236902403786e-08
   16 KSP Residual norm 2.932877082709e-08
   17 KSP Residual norm 3.881909203171e-09
   18 KSP Residual norm 1.107791399514e-09
   19 KSP Residual norm 2.645048006100e-11
  1 KSP Residual norm 8.266776463696e-01
    Residual norms for fieldsplit_FE_split_ solve.
    0 KSP Residual norm 9.262528453386e-08
    1 KSP Residual norm 5.683232925010e-10
    2 KSP Residual norm 1.915223168286e-10
    3 KSP Residual norm 1.397893184942e-10
    4 KSP Residual norm 1.691441435404e-11
    5 KSP Residual norm 6.138315243419e-12
    6 KSP Residual norm 5.576043830003e-12
    7 KSP Residual norm 5.574440028225e-12
    8 KSP Residual norm 5.559544964428e-12
    9 KSP Residual norm 5.539862581746e-12
   10 KSP Residual norm 5.258329460152e-12
   11 KSP Residual norm 2.643581511791e-12
   12 KSP Residual norm 2.641293392449e-12
   13 KSP Residual norm 2.354608977643e-14
  2 KSP Residual norm 4.450925351013e-07
    Residual norms for fieldsplit_FE_split_ solve.
    0 KSP Residual norm 6.653681330477e-14
    1 KSP Residual norm 6.650750698147e-14
    2 KSP Residual norm 6.111123464526e-14
    3 KSP Residual norm 2.026817941567e-14
    4 KSP Residual norm 9.604999144183e-15
    5 KSP Residual norm 9.208296307424e-15
    6 KSP Residual norm 9.196769686859e-15
    7 KSP Residual norm 9.185058975459e-15
    8 KSP Residual norm 9.180207477303e-15
    9 KSP Residual norm 8.991574890909e-15
   10 KSP Residual norm 8.032736869820e-15
   11 KSP Residual norm 1.536409278928e-15
   12 KSP Residual norm 1.177374264280e-15
   13 KSP Residual norm 1.175712092044e-15
   14 KSP Residual norm 2.572275406087e-16
   15 KSP Residual norm 2.548423809711e-16
   16 KSP Residual norm 8.616505207588e-17
   17 KSP Residual norm 7.563053994201e-18
   18 KSP Residual norm 6.807636198601e-18
   19 KSP Residual norm 9.747028518744e-19
   20 KSP Residual norm 2.419807103570e-21
  3 KSP Residual norm 2.986369469883e-09
    Residual norms for fieldsplit_FE_split_ solve.
    0 KSP Residual norm 7.813223137340e-16
    1 KSP Residual norm 4.793103235095e-18
    2 KSP Residual norm 1.615526128222e-18
    3 KSP Residual norm 1.179102504397e-18
    4 KSP Residual norm 1.427467627551e-19
    5 KSP Residual norm 5.177440470993e-20
    6 KSP Residual norm 4.703763659148e-20
    7 KSP Residual norm 4.701953228322e-20
    8 KSP Residual norm 4.689269668869e-20
    9 KSP Residual norm 4.672625361251e-20
   10 KSP Residual norm 4.435174006113e-20
   11 KSP Residual norm 2.229156843383e-20
   12 KSP Residual norm 2.228887211080e-20
   13 KSP Residual norm 3.492936921635e-22
  4 KSP Residual norm 3.753341263086e-15
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