Line data    Source code

       1           0 : // Distributed under the MIT License.
       2             : // See LICENSE.txt for details.
       3             : 
       4             : #pragma once
       5             : 
       6             : #include <bit>
       7             : #include <cmath>
       8             : #include <cstddef>
       9             : #include <optional>
      10             : 
      11             : #include "DataStructures/DataBox/DataBox.hpp"
      12             : #include "Time/AdaptiveSteppingDiagnostics.hpp"
      13             : #include "Time/ChooseLtsStepSize.hpp"
      14             : #include "Time/Tags/HistoryEvolvedVariables.hpp"
      15             : #include "Time/Tags/MinimumTimeStep.hpp"
      16             : #include "Time/Time.hpp"
      17             : #include "Time/TimeStepId.hpp"
      18             : #include "Time/TimeStepRequest.hpp"
      19             : #include "Time/TimeStepRequestProcessor.hpp"
      20             : #include "Time/TimeSteppers/LtsTimeStepper.hpp"
      21             : #include "Utilities/ErrorHandling/Assert.hpp"
      22             : #include "Utilities/ErrorHandling/Error.hpp"
      23             : #include "Utilities/Gsl.hpp"
      24             : #include "Utilities/TMPL.hpp"
      25             : 
      26             : /// \cond
      27             : struct AllStepChoosers;
      28             : namespace Tags {
      29             : struct AdaptiveSteppingDiagnostics;
      30             : struct DataBox;
      31             : struct FixedLtsRatio;
      32             : template <typename Tag>
      33             : struct Next;
      34             : struct StepChoosers;
      35             : struct TimeStep;
      36             : struct TimeStepId;
      37             : template <typename StepperInterface>
      38             : struct TimeStepper;
      39             : }  // namespace Tags
      40             : /// \endcond
      41             : 
      42             : /// \brief Adjust the step size for local time stepping.
      43             : ///
      44             : /// \details
      45             : /// Usually, the new step size is chosen by calling the StepChoosers from
      46             : /// `Tags::StepChoosers`, restricted based on the allowed step sizes at the
      47             : /// current time, and limits from history initialization.
      48             : ///
      49             : /// If `Tags::FixedLtsRatio` is present in the DataBox and not empty, the
      50             : /// StepChoosers are not called and instead the desired step is taken to be the
      51             : /// slab size over that value.  Early in the evolution, the actual chosen step
      52             : /// may differ from this because of restrictions on the allowed step, but all
      53             : /// such restrictions are global and will not result in different decisions for
      54             : /// different elements with the same desired fixed ratio.
      55             : ///
      56             : /// The optional template parameter `StepChoosersToUse` may be used to
      57             : /// indicate a subset of the constructable step choosers to use for the current
      58             : /// application of `ChangeStepSize`. Passing `AllStepChoosers` (default)
      59             : /// indicates that any constructible step chooser may be used. This option is
      60             : /// used when multiple components need to invoke `ChangeStepSize` with step
      61             : /// choosers that may not be compatible with all components.
      62             : template <typename StepChoosersToUse = AllStepChoosers>
      63           1 : struct ChangeStepSize {
      64           0 :   using const_global_cache_tags = tmpl::list<Tags::MinimumTimeStep>;
      65             : 
      66           0 :   using return_tags = tmpl::list<Tags::DataBox>;
      67           0 :   using argument_tags = tmpl::list<>;
      68             : 
      69             :   template <typename DbTags>
      70           0 :   static void apply(const gsl::not_null<db::DataBox<DbTags>*> box) {
      71             :     const auto& time_step_id = db::get<Tags::TimeStepId>(*box);
      72             :     if (time_step_id.substep() != 0) {
      73             :       return;
      74             :     }
      75             : 
      76             :     const LtsTimeStepper& time_stepper =
      77             :         db::get<Tags::TimeStepper<LtsTimeStepper>>(*box);
      78             :     const auto& step_choosers = db::get<Tags::StepChoosers>(*box);
      79             : 
      80             :     using history_tags = ::Tags::get_all_history_tags<DbTags>;
      81             :     bool can_change_step_size = true;
      82             :     tmpl::for_each<history_tags>([&box, &can_change_step_size, &time_stepper,
      83             :                                   &time_step_id](auto tag_v) {
      84             :       if (not can_change_step_size) {
      85             :         return;
      86             :       }
      87             :       using tag = typename decltype(tag_v)::type;
      88             :       const auto& history = db::get<tag>(*box);
      89             :       can_change_step_size =
      90             :           time_stepper.can_change_step_size(time_step_id, history);
      91             :     });
      92             : 
      93             :     const auto current_step = db::get<Tags::TimeStep>(*box);
      94             : 
      95             :     std::optional<size_t> fixed_lts_ratio{};
      96             :     if constexpr (db::tag_is_retrievable_v<Tags::FixedLtsRatio,
      97             :                                            db::DataBox<DbTags>>) {
      98             :       fixed_lts_ratio = db::get<Tags::FixedLtsRatio>(*box);
      99             :     }
     100             : 
     101             :     TimeStepRequestProcessor step_requests(time_step_id.time_runs_forward());
     102             :     if (fixed_lts_ratio.has_value()) {
     103             :       ASSERT(std::popcount(*fixed_lts_ratio) == 1,
     104             :              "fixed_lts_ratio must be a power of 2, not " << *fixed_lts_ratio);
     105             :       step_requests.process(TimeStepRequest{
     106             :           .size_goal =
     107             :               (current_step.slab().duration() / *fixed_lts_ratio).value()});
     108             :     } else {
     109             :       const double last_step_size = current_step.value();
     110             :       for (const auto& step_chooser : step_choosers) {
     111             :         const auto step_request =
     112             :             step_chooser->template desired_step<StepChoosersToUse>(
     113             :                 last_step_size, *box);
     114             :         step_requests.process(step_request);
     115             :       }
     116             :     }
     117             : 
     118             :     if (not can_change_step_size) {
     119             :       step_requests.error_on_hard_limit(
     120             :           current_step.value(),
     121             :           (time_step_id.step_time() + current_step).value());
     122             :       return;
     123             :     }
     124             : 
     125             :     const double desired_step = step_requests.step_size(
     126             :         time_step_id.step_time().value(), current_step.value());
     127             : 
     128             :     // We do this check twice, first on the desired value, and then on
     129             :     // the actual chosen value, which is probably slightly smaller.
     130             :     if (std::abs(desired_step) < db::get<::Tags::MinimumTimeStep>(*box)) {
     131             :       ERROR_NO_TRACE(
     132             :           "Chosen step size "
     133             :           << desired_step << " is smaller than the MinimumTimeStep of "
     134             :           << db::get<::Tags::MinimumTimeStep>(*box)
     135             :           << ".\n"
     136             :              "\n"
     137             :              "This can indicate a flaw in the step chooser, the grid, or a "
     138             :              "simulation instability that an error-based stepper is naively "
     139             :              "attempting to resolve. A possible issue is an aliasing-driven "
     140             :              "instability that could be cured by more aggressive filtering if "
     141             :              "you are using DG.");
     142             :     }
     143             : 
     144             :     const auto new_step =
     145             :         choose_lts_step_size(time_step_id.step_time(), desired_step);
     146             :     step_requests.error_on_hard_limit(
     147             :         new_step.value(), (time_step_id.step_time() + new_step).value());
     148             : 
     149             :     if (new_step == current_step) {
     150             :       return;
     151             :     }
     152             : 
     153             :     if (std::abs(new_step.value()) < db::get<::Tags::MinimumTimeStep>(*box)) {
     154             :       ERROR_NO_TRACE(
     155             :           "Chosen step size after conversion to a fraction of a slab "
     156             :           << new_step << " is smaller than the MinimumTimeStep of "
     157             :           << db::get<::Tags::MinimumTimeStep>(*box)
     158             :           << ".\n"
     159             :              "\n"
     160             :              "This can indicate a flaw in the step chooser, the grid, or a "
     161             :              "simulation instability that an error-based stepper is naively "
     162             :              "attempting to resolve. A possible issue is an aliasing-driven "
     163             :              "instability that could be cured by more aggressive filtering if "
     164             :              "you are using DG.");
     165             :     }
     166             : 
     167             :     db::mutate<Tags::Next<Tags::TimeStepId>, Tags::TimeStep,
     168             :                Tags::AdaptiveSteppingDiagnostics>(
     169             :         [&](const gsl::not_null<TimeStepId*> local_next_time_id,
     170             :             const gsl::not_null<TimeDelta*> time_step,
     171             :             const gsl::not_null<AdaptiveSteppingDiagnostics*> diags) {
     172             :           *time_step = new_step;
     173             :           *local_next_time_id =
     174             :               time_stepper.next_time_id(time_step_id, *time_step);
     175             :           ++diags->number_of_step_fraction_changes;
     176             :         },
     177             :         box);
     178             :   }
     179             : };