Dear DuMux community,
in DuMux 3.7 there are some changes in the parallel linear solver. In DuMux 3.6 we used the following code for the linear solver
using LinearSolver = IstlSolverFactoryBackend<LinearSolverTraits<GridGeometry>>;
for a parallel (MPI) shallow water equations model. In the new version DuMux 3.7, the code/interface has changed and a second argument is needed
using LinearSolver = IstlSolverFactoryBackend<LinearSolverTraits<GridGeometry>, LinearAlgebraTraitsFromAssembler<Assembler>>;
We added the second argument and the code compiles and runs. However, the model runs much slower. It looks like the computation of the residual has changed. With DuMux 3.6 the output of the Newton solver was:
Newton iteration 1 done, maximum relative shift = 6.9188e-02, residual = 1.3174e+01, residual reduction 1.0000e+00->2.0094e-02@lambda=1.0000
Newton iteration 2 done, maximum relative shift = 1.6123e-02, residual = 2.5193e-01, residual reduction 2.0094e-02->3.8426e-04@lambda=1.0000
Newton iteration 3 done, maximum relative shift = 3.1727e-04, residual = 4.9623e-03, residual reduction 3.8426e-04->7.5690e-06@lambda=1.0000
Assemble/solve/update time: 0.044(24.32%)/0.13(71.15%)/0.0082(4.53%)
With DuMux 3.7 the output has changed to
Newton iteration 1 done, maximum relative shift = 6.9188e-02, residual = 1.4379e+02, residual reduction 1.0000e+00->2.1931e-01@lambda=1.0000
Newton iteration 2 done, maximum relative shift = 1.6123e-02, residual = 3.6247e+01, residual reduction 2.1931e-01->5.5287e-02@lambda=1.0000
Newton iteration 3 done, maximum relative shift = 3.1751e-04, residual = 9.2089e+00, residual reduction 5.5287e-02->1.4046e-02@lambda=1.0000
Newton iteration 4 done, maximum relative shift = 2.0686e-05, residual = 2.2909e+00, residual reduction 1.4046e-02->3.4943e-03@lambda=1.0000
Newton iteration 5 done, maximum relative shift = 8.9205e-06, residual = 5.6879e-01, residual reduction 3.4943e-03->8.6757e-04@lambda=1.0000
Newton iteration 6 done, maximum relative shift = 3.6801e-06, residual = 1.3881e-01, residual reduction 8.6757e-04->2.1172e-04@lambda=1.0000
Newton iteration 7 done, maximum relative shift = 1.7669e-06, residual = 3.1597e-02, residual reduction 2.1172e-04->4.8194e-05@lambda=1.0000
Assemble/solve/update time: 0.15(76.02%)/0.029(14.98%)/0.017(9.01%)
While the relative shift remains nearly the same during the first three Newton steps, the residual has increased. I guess that we have just missed to change some further parameters/options to ensure that the residual is computed correctly. Are there any hints and tips?
Best regards,
Leo
Im Auftrag
Dr.-Ing. Leopold Stadler
--
Referat Numerische Verfahren im Wasserbau
Abteilung Wasserbau im Binnenbereich
Bundesanstalt für Wasserbau
Federal Waterways Engineering and Research Institute
Kußmaulstraße 17 | 76187 Karlsruhe
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