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             : #include <type_traits>
      11             : 
      12             : #include "DataStructures/DataBox/DataBox.hpp"
      13             : #include "Time/AdaptiveSteppingDiagnostics.hpp"
      14             : #include "Time/ChooseLtsStepSize.hpp"
      15             : #include "Time/LtsMode.hpp"
      16             : #include "Time/Tags/HistoryEvolvedVariables.hpp"
      17             : #include "Time/Tags/LtsStepChoosers.hpp"
      18             : #include "Time/Tags/MinimumTimeStep.hpp"
      19             : #include "Time/Time.hpp"
      20             : #include "Time/TimeStepId.hpp"
      21             : #include "Time/TimeStepRequest.hpp"
      22             : #include "Time/TimeStepRequestProcessor.hpp"
      23             : #include "Time/TimeSteppers/LtsTimeStepper.hpp"
      24             : #include "Utilities/ErrorHandling/Assert.hpp"
      25             : #include "Utilities/ErrorHandling/Error.hpp"
      26             : #include "Utilities/Gsl.hpp"
      27             : #include "Utilities/TMPL.hpp"
      28             : 
      29             : /// \cond
      30             : struct AllStepChoosers;
      31             : namespace Tags {
      32             : struct AdaptiveSteppingDiagnostics;
      33             : struct DataBox;
      34             : struct FixedLtsRatio;
      35             : struct LtsMode;
      36             : template <typename Tag>
      37             : struct Next;
      38             : struct TimeStep;
      39             : struct TimeStepId;
      40             : template <typename StepperInterface>
      41             : struct TimeStepper;
      42             : }  // namespace Tags
      43             : /// \endcond
      44             : 
      45             : /// \brief Adjust the step size for local time stepping.
      46             : ///
      47             : /// \details
      48             : /// Usually, the new step size is chosen by calling the StepChoosers from
      49             : /// `Tags::LtsStepChoosers`, restricted based on the allowed step sizes at the
      50             : /// current time, and limits from history initialization.
      51             : ///
      52             : /// If `Tags::FixedLtsRatio` is present in the DataBox and not empty, the
      53             : /// StepChoosers are not called and instead the desired step is taken to be the
      54             : /// slab size over that value.  Early in the evolution, the actual chosen step
      55             : /// may differ from this because of restrictions on the allowed step, but all
      56             : /// such restrictions are global and will not result in different decisions for
      57             : /// different elements with the same desired fixed ratio.
      58             : ///
      59             : /// The optional template parameter `StepChoosersToUse` may be used to
      60             : /// indicate a subset of the constructable step choosers to use for the current
      61             : /// application of `ChangeStepSize`. Passing `AllStepChoosers` (default)
      62             : /// indicates that any constructible step chooser may be used. This option is
      63             : /// used when multiple components need to invoke `ChangeStepSize` with step
      64             : /// choosers that may not be compatible with all components.
      65             : template <typename StepChoosersToUse = AllStepChoosers,
      66             :           template <typename> typename CacheTagPrefix = std::type_identity_t>
      67           1 : struct ChangeStepSize {
      68           0 :   using const_global_cache_tags =
      69             :       tmpl::list<CacheTagPrefix<Tags::MinimumTimeStep>,
      70             :                  CacheTagPrefix<Tags::LtsStepChoosers>>;
      71             : 
      72           0 :   using return_tags = tmpl::list<Tags::DataBox>;
      73           0 :   using argument_tags = tmpl::list<>;
      74             : 
      75             :   template <typename DbTags>
      76           0 :   static void apply(const gsl::not_null<db::DataBox<DbTags>*> box) {
      77             :     if (db::get<CacheTagPrefix<Tags::LtsMode>>(*box) == LtsMode::Off) {
      78             :       return;
      79             :     }
      80             : 
      81             :     const auto& time_step_id = db::get<Tags::TimeStepId>(*box);
      82             :     if (time_step_id.substep() != 0) {
      83             :       return;
      84             :     }
      85             : 
      86             :     const LtsTimeStepper& time_stepper =
      87             :         db::get<CacheTagPrefix<Tags::TimeStepper<LtsTimeStepper>>>(*box);
      88             :     const auto& step_choosers =
      89             :         db::get<CacheTagPrefix<Tags::LtsStepChoosers>>(*box);
      90             : 
      91             :     using history_tags = ::Tags::get_all_history_tags<DbTags>;
      92             :     bool can_change_step_size = true;
      93             :     tmpl::for_each<history_tags>([&box, &can_change_step_size, &time_stepper,
      94             :                                   &time_step_id](auto tag_v) {
      95             :       if (not can_change_step_size) {
      96             :         return;
      97             :       }
      98             :       using tag = typename decltype(tag_v)::type;
      99             :       const auto& history = db::get<tag>(*box);
     100             :       can_change_step_size =
     101             :           time_stepper.can_change_step_size(time_step_id, history);
     102             :     });
     103             : 
     104             :     const auto current_step = db::get<Tags::TimeStep>(*box);
     105             : 
     106             :     std::optional<size_t> fixed_lts_ratio{};
     107             :     if constexpr (db::tag_is_retrievable_v<Tags::FixedLtsRatio,
     108             :                                            db::DataBox<DbTags>>) {
     109             :       fixed_lts_ratio = db::get<Tags::FixedLtsRatio>(*box);
     110             :     }
     111             : 
     112             :     TimeStepRequestProcessor step_requests(time_step_id.time_runs_forward());
     113             :     if (fixed_lts_ratio.has_value()) {
     114             :       ASSERT(std::popcount(*fixed_lts_ratio) == 1,
     115             :              "fixed_lts_ratio must be a power of 2, not " << *fixed_lts_ratio);
     116             :       step_requests.process(TimeStepRequest{
     117             :           .size_goal =
     118             :               (current_step.slab().duration() / *fixed_lts_ratio).value()});
     119             :     } else {
     120             :       const double last_step_size = current_step.value();
     121             :       for (const auto& step_chooser : step_choosers) {
     122             :         const auto step_request =
     123             :             step_chooser->template desired_step<StepChoosersToUse>(
     124             :                 last_step_size, *box);
     125             :         step_requests.process(step_request);
     126             :       }
     127             :     }
     128             : 
     129             :     if (not can_change_step_size) {
     130             :       step_requests.error_on_hard_limit(
     131             :           current_step.value(),
     132             :           (time_step_id.step_time() + current_step).value());
     133             :       return;
     134             :     }
     135             : 
     136             :     const double desired_step = step_requests.step_size(
     137             :         time_step_id.step_time().value(), current_step.value());
     138             : 
     139             :     const auto& minimum_time_step =
     140             :         db::get<CacheTagPrefix<::Tags::MinimumTimeStep>>(*box);
     141             : 
     142             :     // We do this check twice, first on the desired value, and then on
     143             :     // the actual chosen value, which is probably slightly smaller.
     144             :     if (std::abs(desired_step) < minimum_time_step) {
     145             :       ERROR_NO_TRACE(
     146             :           "Chosen step size "
     147             :           << desired_step << " is smaller than the MinimumTimeStep of "
     148             :           << minimum_time_step
     149             :           << ".\n"
     150             :              "\n"
     151             :              "This can indicate a flaw in the step chooser, the grid, or a "
     152             :              "simulation instability that an error-based stepper is naively "
     153             :              "attempting to resolve. A possible issue is an aliasing-driven "
     154             :              "instability that could be cured by more aggressive filtering if "
     155             :              "you are using DG.");
     156             :     }
     157             : 
     158             :     const auto new_step =
     159             :         choose_lts_step_size(time_step_id.step_time(), desired_step);
     160             :     step_requests.error_on_hard_limit(
     161             :         new_step.value(), (time_step_id.step_time() + new_step).value());
     162             : 
     163             :     if (new_step == current_step) {
     164             :       return;
     165             :     }
     166             : 
     167             :     if (std::abs(new_step.value()) < minimum_time_step) {
     168             :       ERROR_NO_TRACE(
     169             :           "Chosen step size after conversion to a fraction of a slab "
     170             :           << new_step << " is smaller than the MinimumTimeStep of "
     171             :           << minimum_time_step
     172             :           << ".\n"
     173             :              "\n"
     174             :              "This can indicate a flaw in the step chooser, the grid, or a "
     175             :              "simulation instability that an error-based stepper is naively "
     176             :              "attempting to resolve. A possible issue is an aliasing-driven "
     177             :              "instability that could be cured by more aggressive filtering if "
     178             :              "you are using DG.");
     179             :     }
     180             : 
     181             :     db::mutate<Tags::Next<Tags::TimeStepId>, Tags::TimeStep,
     182             :                Tags::AdaptiveSteppingDiagnostics>(
     183             :         [&](const gsl::not_null<TimeStepId*> local_next_time_id,
     184             :             const gsl::not_null<TimeDelta*> time_step,
     185             :             const gsl::not_null<AdaptiveSteppingDiagnostics*> diags) {
     186             :           *time_step = new_step;
     187             :           *local_next_time_id =
     188             :               time_stepper.next_time_id(time_step_id, *time_step);
     189             :           ++diags->number_of_step_fraction_changes;
     190             :         },
     191             :         box);
     192             :   }
     193             : };