beuler solver timestep and Jacobian calculation#3107
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The preconditioner depends on the timestep, so avoid changing timestep unless necessary. Allow timesteps to go past output time, then interpolate. If timesteps are adjusted then recalculate the Jacobian. This could be optimised to update the Jacobian and recalculate the preconditioner, without finite differencing the RHS.
New tunable inputs for adjustment when timestep fails, and when number of iterations is either too high or too low.
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| int loop_count = 0; | ||
| do { | ||
| if (simtime >= target) | ||
| break; // Could happen if step over multiple outputs |
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warning: statement should be inside braces [readability-braces-around-statements]
Suggested change
| break; // Could happen if step over multiple outputs | |
| if (simtime >= target) { | |
| break; // Could happen if step over multiple outputs | |
| } |
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| // Note: If simtime = target then alpha = 0 | ||
| // and output_x = snes_x | ||
| BoutReal alpha = (simtime - target) / dt; |
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warning: variable 'alpha' of type 'BoutReal' (aka 'double') can be declared 'const' [misc-const-correctness]
Suggested change
| BoutReal alpha = (simtime - target) / dt; | |
| xconst |
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This looks reasonable to me, but I thought PETSc could do this sort of interpolate automatically? Is it just easier to do this interpolation ourselves? |
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The Jacobian that SNES uses for preconditioning depends on the timestep, so when the timestep is changed the preconditioner becomes less effective unless it is recalculated.
Adding more tuning parameters, will need to optimise for problems of interest.