SNES timestep control changes#3273
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Allows the target to be set to push timestep rather than stall once reaching a set number of iterations.
Calculates a moving average of recent SNES failures. Enables timestep controllers to be more cautious when SNES is repeatedly failing.
Separate out the global timestep control into a function
Now always calculates local and global residuals. If pseudo timestepping is used then another loop over variables is used to update per-cell timesteps and set `dt_vec`. When `diagnose=true`, the local residual will be saved as `snes_local_residual`, and the global residual will be printed after each internal timestep.
Selects the trigger for writing an output. The default is `fixed_time_interval` that outputs at regular time intervals. Other choice is `residual_ratio` that outputs when the global residual falls by a factor `output_residual_ratio`.
Describe new settings `timestep_control` and `output_trigger` that select different strategies to adjust global timesteps and output simulation state.
Save the global residual diagnostic
Uses setting `pid_controller` rather than `pid_nonlinear_its`.
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| int loop_count = 0; | ||
| recent_failure_rate = 0.0; | ||
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| BoutReal start_global_residual = global_residual; |
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warning: variable 'start_global_residual' of type 'BoutReal' (aka 'double') can be declared 'const' [misc-const-correctness]
| BoutReal start_global_residual = global_residual; | |
| BoutReal const start_global_residual = global_residual; |
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| return timestep; // No change | ||
| } |
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^| } | ||
| return timestep; // No change | ||
| } | ||
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^| PetscCall(rhs_function(x, snes_f, false)); | ||
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| // Reading the residual vectors | ||
| const BoutReal* current_residual = nullptr; |
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warning: pointee of variable 'mesh' of type 'Mesh *' can be declared 'const' [misc-const-correctness]
| const BoutReal* current_residual = nullptr; | |
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warning: no header providing "mean" is directly included [misc-include-cleaner]
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^False by default. If true, re-uses the Jacobian and preconditioner across SNES calls.
| int loop_count = 0; | ||
| recent_failure_rate = 0.0; | ||
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| BoutReal start_global_residual = global_residual; |
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warning: avoid do-while loops [cppcoreguidelines-avoid-do-while]
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| PetscErrorCode SNESSolver::updateResiduals(Vec x) { | ||
| // Push residuals to previous residuals | ||
| // Copying so that data is not shared |
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^| PetscErrorCode SNESSolver::updateResiduals(Vec x) { | ||
| // Push residuals to previous residuals | ||
| // Copying so that data is not shared | ||
| local_residual_prev = copy(local_residual); |
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^| PetscCall(VecGetArrayRead(snes_f, ¤t_residual)); | ||
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| // Note: The ordering of quantities in the PETSc vectors | ||
| // depends on the Solver::loop_vars function |
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warning: pointee of variable 'mesh' of type 'Mesh *' can be declared 'const' [misc-const-correctness]
| // depends on the Solver::loop_vars function | |
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| // Restore Vec data arrays | ||
| PetscCall(VecRestoreArrayRead(snes_f, ¤t_residual)); | ||
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| // Global residual metric (RMS) |
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warning: no header providing "mean" is directly included [misc-include-cleaner]
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2 participants
timestep_controlreplacespid_controllerboolean. Choices are:pid_nonlinear_itsthat uses a PID controller and the nonlinear iteration count. This is now the default.residual_ratiothat uses the ratio of the global residual (Root-Mean-Square of the time derivatives, averaged over all fields and cells). The algorithm is taken from PETSc TSPSEUDO: https://petsc.org/release/manualpages/TS/TSPSEUDO/ .threshold_nonlinear_itsis the previous default, that increases and decreases timestep based on thresholds in the number of nonlinear iterationsfixedis for testing; no timestep controloutput_triggerchanges when outputs are written:fixed_time_intervalis the default, outputting at regular time intervals.residual_ratiooutputs when the global residual has reduced below a given factor (output_residual_ratiooption, default 0.5) times the residual at the previous output. This is a useful measure of progress towards steady state.