[petsc-users] CPR-AMG: SNES with two cores worse than with one

Robert Annewandter robert.annewandter at opengosim.com
Thu Jul 6 14:03:04 CDT 2017


Hi all,

I like to understand why the SNES of my CPR-AMG Two-Stage Preconditioner
(with KSPFGMRES + multipl. PCComposite (PCGalerkin with KSPGMRES +
BoomerAMG, PCBJacobi + PCLU init) on a 24,000 x 24,000 matrix) struggles
to converge when using two cores instead of one. Because of the adaptive
time stepping of the Newton, this leads to severe cuts in time step.

This is how I run it with two cores

mpirun \
  -n 2 pflotran \
  -pflotranin het.pflinput \
  -ksp_monitor_true_residual \
  -flow_snes_view \
  -flow_snes_converged_reason \
  -flow_sub_1_pc_type bjacobi \
  -flow_sub_1_sub_pc_type lu \
  -flow_sub_1_sub_pc_factor_pivot_in_blocks true\
  -flow_sub_1_sub_pc_factor_nonzeros_along_diagonal \
  -options_left \
  -log_summary \
  -info


With one core I get (after grepping the crap away from -info):

 Step     32 Time=  1.80000E+01

[...]

  0 2r: 1.58E-02 2x: 0.00E+00 2u: 0.00E+00 ir: 7.18E-03 iu: 0.00E+00
rsn:   0
[0] SNESComputeJacobian(): Rebuilding preconditioner
    Residual norms for flow_ solve.
    0 KSP unpreconditioned resid norm 1.581814306485e-02 true resid norm
1.581814306485e-02 ||r(i)||/||b|| 1.000000000000e+00
      Residual norms for flow_sub_0_galerkin_ solve.
      0 KSP preconditioned resid norm 5.697603110484e+07 true resid norm
5.175721849125e+03 ||r(i)||/||b|| 5.037527476892e+03
      1 KSP preconditioned resid norm 5.041509073319e+06 true resid norm
3.251596928176e+02 ||r(i)||/||b|| 3.164777657484e+02
      2 KSP preconditioned resid norm 1.043761838360e+06 true resid norm
8.957519558348e+01 ||r(i)||/||b|| 8.718349288342e+01
      3 KSP preconditioned resid norm 1.129189815646e+05 true resid norm
2.722436912053e+00 ||r(i)||/||b|| 2.649746479496e+00
      4 KSP preconditioned resid norm 8.829637298082e+04 true resid norm
8.026373593492e+00 ||r(i)||/||b|| 7.812065388300e+00
      5 KSP preconditioned resid norm 6.506021637694e+04 true resid norm
3.479889319880e+00 ||r(i)||/||b|| 3.386974527698e+00
      6 KSP preconditioned resid norm 6.392263200180e+04 true resid norm
3.819202631980e+00 ||r(i)||/||b|| 3.717228003987e+00
      7 KSP preconditioned resid norm 2.464946645480e+04 true resid norm
7.329964753388e-01 ||r(i)||/||b|| 7.134251013911e-01
      8 KSP preconditioned resid norm 2.603879153772e+03 true resid norm
2.035525412004e-02 ||r(i)||/||b|| 1.981175861414e-02
      9 KSP preconditioned resid norm 1.774410462754e+02 true resid norm
3.001214973121e-03 ||r(i)||/||b|| 2.921081026352e-03
    10 KSP preconditioned resid norm 1.664227038378e+01 true resid norm
3.413136309181e-04 ||r(i)||/||b|| 3.322003855903e-04
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
1.131868956745e+00 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 2.067297386780e+07 at iteration 11
    11 KSP preconditioned resid norm 1.131868956745e+00 true resid norm
1.526261825526e-05 ||r(i)||/||b|| 1.485509868409e-05
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
2.148515820410e-14 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 1.581814306485e-02 at iteration 1
    1 KSP unpreconditioned resid norm 2.148515820410e-14 true resid norm
2.148698024622e-14 ||r(i)||/||b|| 1.358375642332e-12
[0] SNESSolve_NEWTONLS(): iter=0, linear solve iterations=1
[0] SNESNEWTONLSCheckResidual_Private(): ||J^T(F-Ax)||/||F-AX||
3.590873180642e-01 near zero implies inconsistent rhs
[0] SNESSolve_NEWTONLS(): fnorm=1.5818143064846742e-02,
gnorm=1.0695649833687331e-02, ynorm=4.6826522561266171e+02, lssucceed=0
[0] SNESConvergedDefault(): Converged due to small update length:
4.682652256127e+02 < 1.000000000000e-05 * 3.702480426117e+09
  1 2r: 1.07E-02 2x: 3.70E+09 2u: 4.68E+02 ir: 5.05E-03 iu: 4.77E+01
rsn: stol
Nonlinear flow_ solve converged due to CONVERGED_SNORM_RELATIVE iterations 1



But with two cores I get:


 Step     32 Time=  1.80000E+01

[...]

  0 2r: 6.16E-03 2x: 0.00E+00 2u: 0.00E+00 ir: 3.63E-03 iu: 0.00E+00
rsn:   0
[0] SNESComputeJacobian(): Rebuilding preconditioner

    Residual norms for flow_ solve.
    0 KSP unpreconditioned resid norm 6.162760088924e-03 true resid norm
6.162760088924e-03 ||r(i)||/||b|| 1.000000000000e+00
      Residual norms for flow_sub_0_galerkin_ solve.
      0 KSP preconditioned resid norm 8.994949630499e+08 true resid norm
7.982144380936e-01 ||r(i)||/||b|| 1.000000000000e+00
      1 KSP preconditioned resid norm 8.950556502615e+08 true resid norm
1.550138696155e+00 ||r(i)||/||b|| 1.942007839218e+00
      2 KSP preconditioned resid norm 1.044849684205e+08 true resid norm
2.166193480531e+00 ||r(i)||/||b|| 2.713798920631e+00
      3 KSP preconditioned resid norm 8.209708619718e+06 true resid norm
3.076045005154e-01 ||r(i)||/||b|| 3.853657436340e-01
      4 KSP preconditioned resid norm 3.027461352422e+05 true resid norm
1.207731865714e-02 ||r(i)||/||b|| 1.513041869549e-02
      5 KSP preconditioned resid norm 1.595302164817e+04 true resid norm
4.123713694368e-04 ||r(i)||/||b|| 5.166172769585e-04
      6 KSP preconditioned resid norm 1.898935810797e+03 true resid norm
8.275885058330e-05 ||r(i)||/||b|| 1.036799719897e-04
      7 KSP preconditioned resid norm 1.429881682558e+02 true resid norm
4.751240525466e-06 ||r(i)||/||b|| 5.952335987324e-06
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
8.404003313455e+00 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 8.994949630499e+08 at iteration 8
      8 KSP preconditioned resid norm 8.404003313455e+00 true resid norm
3.841921844578e-07 ||r(i)||/||b|| 4.813145016211e-07
    1 KSP unpreconditioned resid norm 6.162162548202e-03 true resid norm
6.162162548202e-03 ||r(i)||/||b|| 9.999030400804e-01
      Residual norms for flow_sub_0_galerkin_ solve.
      0 KSP preconditioned resid norm 4.360556381209e+07 true resid norm
1.000000245433e+00 ||r(i)||/||b|| 1.000000000000e+00
      1 KSP preconditioned resid norm 5.385519331932e+06 true resid norm
8.785183939860e-02 ||r(i)||/||b|| 8.785181783689e-02
      2 KSP preconditioned resid norm 4.728931283459e+05 true resid norm
2.008708805316e-02 ||r(i)||/||b|| 2.008708312313e-02
      3 KSP preconditioned resid norm 2.734215698319e+04 true resid norm
6.418720397673e-03 ||r(i)||/||b|| 6.418718822309e-03
      4 KSP preconditioned resid norm 1.002270029334e+04 true resid norm
4.040289515991e-03 ||r(i)||/||b|| 4.040288524372e-03
      5 KSP preconditioned resid norm 1.321280190971e+03 true resid norm
1.023292238313e-04 ||r(i)||/||b|| 1.023291987163e-04
      6 KSP preconditioned resid norm 6.594292964815e+01 true resid norm
1.877106733170e-06 ||r(i)||/||b|| 1.877106272467e-06
      7 KSP preconditioned resid norm 7.816325147216e+00 true resid norm
2.552611664980e-07 ||r(i)||/||b|| 2.552611038486e-07
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
6.391568446109e-01 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 4.360556381209e+07 at iteration 8
      8 KSP preconditioned resid norm 6.391568446109e-01 true resid norm
1.680724939670e-08 ||r(i)||/||b|| 1.680724527166e-08
    2 KSP unpreconditioned resid norm 4.328902922753e-07 true resid norm
4.328902922752e-07 ||r(i)||/||b|| 7.024292460341e-05
      Residual norms for flow_sub_0_galerkin_ solve.
      0 KSP preconditioned resid norm 8.794597825780e+08 true resid norm
1.000000094566e+00 ||r(i)||/||b|| 1.000000000000e+00
      1 KSP preconditioned resid norm 8.609906572102e+08 true resid norm
2.965044981249e+00 ||r(i)||/||b|| 2.965044700856e+00
      2 KSP preconditioned resid norm 9.318108989314e+07 true resid norm
1.881262939380e+00 ||r(i)||/||b|| 1.881262761477e+00
      3 KSP preconditioned resid norm 6.908723262483e+06 true resid norm
2.639592490398e-01 ||r(i)||/||b|| 2.639592240782e-01
      4 KSP preconditioned resid norm 2.651677791227e+05 true resid norm
9.736480169584e-03 ||r(i)||/||b|| 9.736479248845e-03
      5 KSP preconditioned resid norm 1.192178471172e+04 true resid norm
3.082839752692e-04 ||r(i)||/||b|| 3.082839461160e-04
      6 KSP preconditioned resid norm 1.492201446262e+03 true resid norm
4.633866284506e-05 ||r(i)||/||b|| 4.633865846301e-05
      7 KSP preconditioned resid norm 1.160670017241e+02 true resid norm
2.821157348522e-06 ||r(i)||/||b|| 2.821157081737e-06
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
6.447568262216e+00 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 8.794597825780e+08 at iteration 8
      8 KSP preconditioned resid norm 6.447568262216e+00 true resid norm
1.516068561348e-07 ||r(i)||/||b|| 1.516068417980e-07
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
6.135731709822e-15 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 6.162760088924e-03 at iteration 3
    3 KSP unpreconditioned resid norm 6.135731709822e-15 true resid norm
1.142020328809e-14 ||r(i)||/||b|| 1.853098793933e-12

[0] SNESSolve_NEWTONLS(): iter=0, linear solve iterations=3
[0] SNESNEWTONLSCheckResidual_Private(): ||J^T(F-Ax)||/||F-AX||
1.998388224666e-02 near zero implies inconsistent rhs
[0] SNESSolve_NEWTONLS(): fnorm=6.1627600889243711e-03,
gnorm=1.0406503258190572e-02, ynorm=6.2999025681245366e+04, lssucceed=0  
  1 2r: 1.04E-02 2x: 3.70E+09 2u: 6.30E+04 ir: 6.54E-03 iu: 5.00E+04
rsn:   0
[0] SNESComputeJacobian(): Rebuilding preconditioner

    Residual norms for flow_ solve.
    0 KSP unpreconditioned resid norm 1.040650325819e-02 true resid norm
1.040650325819e-02 ||r(i)||/||b|| 1.000000000000e+00
      Residual norms for flow_sub_0_galerkin_ solve.
      0 KSP preconditioned resid norm 6.758906811264e+07 true resid norm
9.814998431686e-01 ||r(i)||/||b|| 1.000000000000e+00
      1 KSP preconditioned resid norm 2.503922806424e+06 true resid norm
2.275130113021e-01 ||r(i)||/||b|| 2.318013730574e-01
      2 KSP preconditioned resid norm 3.316753614870e+05 true resid norm
3.820733530238e-02 ||r(i)||/||b|| 3.892750016040e-02
      3 KSP preconditioned resid norm 2.956751700483e+04 true resid norm
2.143772538677e-03 ||r(i)||/||b|| 2.184180215207e-03
      4 KSP preconditioned resid norm 1.277067042524e+03 true resid norm
9.093614251311e-05 ||r(i)||/||b|| 9.265018547485e-05
      5 KSP preconditioned resid norm 1.060996002446e+02 true resid norm
1.042893700050e-05 ||r(i)||/||b|| 1.062551061326e-05
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
5.058127343285e+00 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 6.758906811264e+07 at iteration 6
      6 KSP preconditioned resid norm 5.058127343285e+00 true resid norm
4.054770602120e-07 ||r(i)||/||b|| 4.131198420807e-07
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
4.449606189225e-10 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 1.040650325819e-02 at iteration 1
    1 KSP unpreconditioned resid norm 4.449606189225e-10 true resid norm
4.449606189353e-10 ||r(i)||/||b|| 4.275793779098e-08

[0] SNESSolve_NEWTONLS(): iter=1, linear solve iterations=1
[0] SNESNEWTONLSCheckResidual_Private(): ||J^T(F-Ax)||/||F-AX||
4.300066663571e-02 near zero implies inconsistent rhs
[0] SNESSolve_NEWTONLS(): fnorm=1.0406503258190572e-02,
gnorm=7.3566280848133728e-02, ynorm=7.9500485128639993e+04, lssucceed=0
  2 2r: 7.36E-02 2x: 3.70E+09 2u: 7.95E+04 ir: 4.62E-02 iu: 5.00E+04
rsn:   0
[0] SNESComputeJacobian(): Rebuilding preconditioner

    Residual norms for flow_ solve.
    0 KSP unpreconditioned resid norm 7.356628084813e-02 true resid norm
7.356628084813e-02 ||r(i)||/||b|| 1.000000000000e+00
      Residual norms for flow_sub_0_galerkin_ solve.
      0 KSP preconditioned resid norm 7.253424029194e+06 true resid norm
9.647008645250e-01 ||r(i)||/||b|| 1.000000000000e+00
      1 KSP preconditioned resid norm 7.126940190688e+06 true resid norm
1.228009197928e+00 ||r(i)||/||b|| 1.272942984800e+00
      2 KSP preconditioned resid norm 9.391591432635e+05 true resid norm
7.804929162756e-01 ||r(i)||/||b|| 8.090517433711e-01
      3 KSP preconditioned resid norm 6.538499674761e+04 true resid norm
5.503467432893e-02 ||r(i)||/||b|| 5.704843475602e-02
      4 KSP preconditioned resid norm 1.593713396575e+04 true resid norm
8.902701363763e-02 ||r(i)||/||b|| 9.228457951208e-02
      5 KSP preconditioned resid norm 4.837260621464e+02 true resid norm
2.966772992825e-03 ||r(i)||/||b|| 3.075329464213e-03
      6 KSP preconditioned resid norm 1.681372767335e+02 true resid norm
5.312467443025e-04 ||r(i)||/||b|| 5.506854651406e-04
      7 KSP preconditioned resid norm 1.271478850717e+01 true resid norm
2.123810020488e-05 ||r(i)||/||b|| 2.201521838103e-05
      8 KSP preconditioned resid norm 1.262723712696e+00 true resid norm
1.150572715331e-06 ||r(i)||/||b|| 1.192673042641e-06
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
9.053072585125e-02 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 7.253424029194e+06 at iteration 9
      9 KSP preconditioned resid norm 9.053072585125e-02 true resid norm
9.475050575058e-08 ||r(i)||/||b|| 9.821749853747e-08
    1 KSP unpreconditioned resid norm 8.171589173162e-03 true resid norm
8.171589173162e-03 ||r(i)||/||b|| 1.110779161180e-01
      Residual norms for flow_sub_0_galerkin_ solve.
      0 KSP preconditioned resid norm 4.345765068989e+07 true resid norm
9.999992231691e-01 ||r(i)||/||b|| 1.000000000000e+00
      1 KSP preconditioned resid norm 5.388715093466e+06 true resid norm
8.125387327699e-02 ||r(i)||/||b|| 8.125393639755e-02
      2 KSP preconditioned resid norm 4.763725726436e+05 true resid norm
2.464285618036e-02 ||r(i)||/||b|| 2.464287532371e-02
      3 KSP preconditioned resid norm 2.287746683380e+04 true resid norm
7.224823080100e-03 ||r(i)||/||b|| 7.224828692570e-03
      4 KSP preconditioned resid norm 4.872858764091e+03 true resid norm
3.972261388893e-03 ||r(i)||/||b|| 3.972264474670e-03
      5 KSP preconditioned resid norm 8.670449895323e+02 true resid norm
2.359005963873e-04 ||r(i)||/||b|| 2.359007796423e-04
      6 KSP preconditioned resid norm 4.252589693890e+01 true resid norm
1.471904261226e-06 ||r(i)||/||b|| 1.471905404648e-06
      7 KSP preconditioned resid norm 5.128476471782e+00 true resid norm
1.643725157865e-07 ||r(i)||/||b|| 1.643726434763e-07
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
4.311901915856e-01 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 4.345765068989e+07 at iteration 8
      8 KSP preconditioned resid norm 4.311901915856e-01 true resid norm
1.166123921637e-08 ||r(i)||/||b|| 1.166124827519e-08
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
2.373662391739e-09 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 7.356628084813e-02 at iteration 2
    2 KSP unpreconditioned resid norm 2.373662391739e-09 true resid norm
2.373662391658e-09 ||r(i)||/||b|| 3.226562990941e-08

[0] SNESSolve_NEWTONLS(): iter=2, linear solve iterations=2
[0] SNESNEWTONLSCheckResidual_Private(): ||J^T(F-Ax)||/||F-AX||
4.343326231305e-02 near zero implies inconsistent rhs
[0] SNESSolve_NEWTONLS(): fnorm=7.3566280848133728e-02,
gnorm=7.2259942496422647e-02, ynorm=6.3156901950486099e+04, lssucceed=0
  3 2r: 7.23E-02 2x: 3.70E+09 2u: 6.32E+04 ir: 4.52E-02 iu: 5.00E+04
rsn:   0
[0] SNESComputeJacobian(): Rebuilding preconditioner

    Residual norms for flow_ solve.
    0 KSP unpreconditioned resid norm 7.225994249642e-02 true resid norm
7.225994249642e-02 ||r(i)||/||b|| 1.000000000000e+00
      Residual norms for flow_sub_0_galerkin_ solve.
      0 KSP preconditioned resid norm 7.705582590638e+05 true resid norm
9.649751442741e-01 ||r(i)||/||b|| 1.000000000000e+00
      1 KSP preconditioned resid norm 2.444424220392e+04 true resid norm
8.243110200738e-03 ||r(i)||/||b|| 8.542303135630e-03
      2 KSP preconditioned resid norm 2.080899648412e+03 true resid norm
7.642343147053e-04 ||r(i)||/||b|| 7.919730567570e-04
      3 KSP preconditioned resid norm 9.911171129874e+02 true resid norm
5.904182179180e-05 ||r(i)||/||b|| 6.118481096859e-05
      4 KSP preconditioned resid norm 5.258230282482e+02 true resid norm
2.043366677644e-04 ||r(i)||/||b|| 2.117532964210e-04
      5 KSP preconditioned resid norm 5.522830460456e+01 true resid norm
1.710780366056e-05 ||r(i)||/||b|| 1.772875059225e-05
      6 KSP preconditioned resid norm 5.922280741715e+00 true resid norm
1.543198740828e-06 ||r(i)||/||b|| 1.599210870855e-06
      7 KSP preconditioned resid norm 3.339500859115e-01 true resid norm
1.221335666427e-07 ||r(i)||/||b|| 1.265665414984e-07
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
3.329208597672e-02 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 7.705582590638e+05 at iteration 8
      8 KSP preconditioned resid norm 3.329208597672e-02 true resid norm
9.758240835324e-09 ||r(i)||/||b|| 1.011242713683e-08
[0] KSPConvergedDefault(): Linear solver has converged. Residual norm
2.697128456432e-11 is less than relative tolerance 1.000000000000e-07
times initial right hand side norm 7.225994249642e-02 at iteration 1
    1 KSP unpreconditioned resid norm 2.697128456432e-11 true resid norm
2.697128457142e-11 ||r(i)||/||b|| 3.732536124389e-10

[0] SNESSolve_NEWTONLS(): iter=3, linear solve iterations=1
[0] SNESNEWTONLSCheckResidual_Private():
||J^T(F-Ax)||/||F-AX||4.329227684222e-02 near zero implies inconsistent rhs
[0] SNESSolve_NEWTONLS(): fnorm=7.2259942496422647e-02,
gnorm=5.4435602192925014e-01, ynorm=2.7049750229137400e+04, lssucceed=0
[0] SNESConvergedDefault(): Converged due to small update length:
2.704975022914e+04 < 1.000000000000e-05 * 3.702469482296e+09
  4 2r: 5.44E-01 2x: 3.70E+09 2u: 2.70E+04 ir: 3.84E-01 iu: 2.34E+04
rsn: stol
Nonlinear flow_ solve converged due to CONVERGED_SNORM_RELATIVE iterations 4


As the simulation advances this behaviour leads to frequent time step
cuts because of 8 subsequently failed Newton iterations, which brings
the simulation practically to a halt.

Is the Block Jacobi not a good choice? Better ASM with huge overlap? Or
is there something wrong with my RHS? Maybe the SNES, SNESLS, KSP
tolerances need better tuning?

Grateful for any clarifying words!
Robert


My SNES_view is:


SNES Object: (flow_) 2 MPI processes
  type: newtonls
  maximum iterations=8, maximum function evaluations=10000
  tolerances: relative=1e-05, absolute=1e-05, solution=1e-05
  total number of linear solver iterations=1
  total number of function evaluations=2
  norm schedule ALWAYS
  SNESLineSearch Object: (flow_) 2 MPI processes
    type: basic
    maxstep=1.000000e+08, minlambda=1.000000e-05
    tolerances: relative=1.000000e-05, absolute=1.000000e-05,
lambda=1.000000e-08
    maximum iterations=40
    using user-defined precheck step
  KSP Object: (flow_) 2 MPI processes
    type: fgmres
      GMRES: restart=30, using Classical (unmodified) Gram-Schmidt
Orthogonalization with no iterative refinement
      GMRES: happy breakdown tolerance 1e-30
    maximum iterations=200, initial guess is zero
    tolerances:  relative=1e-07, absolute=1e-50, divergence=10000.
    right preconditioning
    using UNPRECONDITIONED norm type for convergence test
  PC Object: (flow_) 2 MPI processes
    type: composite
    Composite PC type - MULTIPLICATIVE
    PCs on composite preconditioner follow
    ---------------------------------
      PC Object: (flow_sub_0_) 2 MPI processes
        type: galerkin
        Galerkin PC
        KSP on Galerkin follow
        ---------------------------------
        KSP Object: (flow_sub_0_galerkin_) 2 MPI processes
          type: gmres
            GMRES: restart=30, using Classical (unmodified) Gram-Schmidt
Orthogonalization with no iterative refinement
            GMRES: happy breakdown tolerance 1e-30
          maximum iterations=200, initial guess is zero
          tolerances:  relative=1e-07, absolute=1e-50, divergence=10000.
          left preconditioning
          using PRECONDITIONED norm type for convergence test
        PC Object: (flow_sub_0_galerkin_) 2 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 0.25
            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: Not using more complex smoothers.
            HYPRE BoomerAMG: Measure type        local
            HYPRE BoomerAMG: Coarsen type        Falgout
            HYPRE BoomerAMG: Interpolation type  classical
          linear system matrix = precond matrix:
          Mat Object: 2 MPI processes
            type: mpiaij
            rows=8000, cols=8000
            total: nonzeros=53600, allocated nonzeros=53600
            total number of mallocs used during MatSetValues calls =0
              not using I-node (on process 0) routines
        linear system matrix = precond matrix:
        Mat Object: (flow_) 2 MPI processes
          type: mpibaij
          rows=24000, cols=24000, bs=3
          total: nonzeros=482400, allocated nonzeros=482400
          total number of mallocs used during MatSetValues calls =0
      PC Object: (flow_sub_1_) 2 MPI processes
        type: bjacobi
          block Jacobi: number of blocks = 2
          Local solve is same for all blocks, in the following KSP and
PC objects:
        KSP Object: (flow_sub_1_sub_) 1 MPI processes
          type: preonly
          maximum iterations=10000, initial guess is zero
          tolerances:  relative=1e-05, absolute=1e-50,
divergence=10000.     <------ not working: -flow_sub_1_sub_ksp_rtol 1e-7
          left preconditioning
          using NONE norm type for convergence test
        PC Object: (flow_sub_1_sub_) 1 MPI processes
          type: lu
            out-of-place factorization
            tolerance for zero pivot 2.22045e-14
            matrix ordering: nd
            factor fill ratio given 5., needed 18.3108
              Factored matrix follows:
                Mat Object: 1 MPI processes
                  type: seqbaij
                  rows=12000, cols=12000, bs=3
                  package used to perform factorization: petsc
                  total: nonzeros=4350654, allocated nonzeros=4350654
                  total number of mallocs used during MatSetValues calls =0
                      block size is 3
          linear system matrix = precond matrix:
          Mat Object: (flow_) 1 MPI processes
            type: seqbaij
            rows=12000, cols=12000, bs=3
            total: nonzeros=237600, allocated nonzeros=237600
            total number of mallocs used during MatSetValues calls =0
                block size is 3
        linear system matrix = precond matrix:
        Mat Object: (flow_) 2 MPI processes
          type: mpibaij
          rows=24000, cols=24000, bs=3
          total: nonzeros=482400, allocated nonzeros=482400
          total number of mallocs used during MatSetValues calls =0
    ---------------------------------
    linear system matrix = precond matrix:
    Mat Object: (flow_) 2 MPI processes
      type: mpibaij
      rows=24000, cols=24000, bs=3
      total: nonzeros=482400, allocated nonzeros=482400
      total number of mallocs used during MatSetValues calls =0
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