limiter.h

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//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Copyright (C) 2023 - 2025 by the ryujin authors
//
 
#pragma once
 
#include <compile_time_options.h>
 
#include "hyperbolic_system.h"
 
#include <compile_time_options.h>
#include <multicomponent_vector.h>
#include <newton.h>
#include <observer_pointer.h>
#include <simd.h>
 
namespace ryujin
{
  namespace Skeleton
  {
    template <int dim, typename Number = double>
    class LimiterView;
 
    template <typename ScalarNumber = double>
    class Limiter : public dealii::ParameterAcceptor
    {
    public:
 
      template <int dim, typename Number = double>
      using View = LimiterView<dim, Number>;
 
 
 
      Limiter(const HyperbolicSystem &hyperbolic_system,
              const std::string &subsection = "/Limiter")
          : ParameterAcceptor(subsection)
          , hyperbolic_system_(&hyperbolic_system)
      {
        iterations_ = 2;
        add_parameter(
            "iterations", iterations_, "Number of limiter iterations");
      }
 
      template <int dim, typename Number>
      auto view() const
      {
        return View<dim, Number>{
            hyperbolic_system_->template view<dim, Number>(), *this};
      }
 
    private:
 
 
      unsigned int iterations_;
 
 
 
      dealii::ObserverPointer<const HyperbolicSystem> hyperbolic_system_;
 
 
      template <int, typename>
      friend class LimiterView;
    };
 
 
    template <int dim, typename Number>
    class LimiterView
    {
    public:
 
      using View = HyperbolicSystemView<dim, Number>;
 
      using ScalarNumber = typename View::ScalarNumber;
 
      using state_type = typename View::state_type;
 
      using flux_contribution_type = typename View::flux_contribution_type;
 
      using PrecomputedVectorView = typename View::PrecomputedVectorView;
 
 
      static constexpr unsigned int n_bounds = 0;
 
      using Bounds = std::array<Number, n_bounds>;
 
      LimiterView(const View &view, const Limiter<ScalarNumber> &limiter)
          : view_(view)
          , limiter_(limiter)
      {
      }
 
      unsigned int iterations() const
      {
        return limiter_.iterations_;
      }
 
      Bounds projection_bounds_from_state(const PrecomputedVectorView & /*pv*/,
                                          const unsigned int /*i*/,
                                          const state_type & /*U_i*/) const
      {
        return Bounds{};
      }
 
      Bounds combine_bounds(const Bounds & /*bounds_left*/,
                            const Bounds & /*bounds_right*/) const
      {
        return Bounds{};
      }
 
      Bounds fully_relax_bounds(const Bounds & /*bounds*/,
                                const Number & /*hd*/) const
      {
        return Bounds{};
      }
 
 
 
      void reset(const PrecomputedVectorView & /*pv*/,
                 const unsigned int /*i*/,
                 const state_type & /*U_i*/,
                 const flux_contribution_type & /*flux_i*/)
      {
        // empty
      }
 
      void accumulate(const PrecomputedVectorView & /*pv*/,
                      const unsigned int * /*js*/,
                      const state_type & /*U_j*/,
                      const flux_contribution_type & /*flux_j*/,
                      const dealii::Tensor<1, dim, Number> & /*scaled_c_ij*/,
                      const state_type & /*affine_shift*/)
      {
        // empty
      }
 
      Bounds bounds(const Number hd_i) const
      {
        auto relaxed_bounds = fully_relax_bounds(bounds_, hd_i);
 
        return relaxed_bounds;
      }
 
 
 
      std::tuple<Number, bool> limit(const Bounds & /*bounds*/,
                                     const state_type & /*U*/,
                                     const state_type & /*P*/,
                                     const Number /*t_min*/ = Number(0.),
                                     const Number t_max = Number(1.)) const
      {
        return {t_max, true};
      }
 
    private:
 
 
      const View view_;
      const Limiter<ScalarNumber> &limiter_;
 
      Bounds bounds_;
    };
  } // namespace Skeleton
} // namespace ryujin