indicator.h

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//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Copyright (C) 2023 - 2026 by the ryujin authors
//
 
#pragma once
 
#include <compile_time_options.h>
 
#include "hyperbolic_system.h"
 
#include <multicomponent_vector.h>
#include <observer_pointer.h>
#include <simd.h>
 
#include <deal.II/base/parameter_acceptor.h>
#include <deal.II/base/vectorization.h>
 
 
namespace ryujin
{
  namespace ScalarConservation
  {
    template <int dim, typename Number = double>
    class IndicatorView;
 
    template <typename ScalarNumber = double>
    class Indicator : public dealii::ParameterAcceptor
    {
    public:
 
      template <int dim, typename Number = double>
      using View = IndicatorView<dim, Number>;
 
 
 
      Indicator(const HyperbolicSystem &hyperbolic_system,
                const std::string &subsection = "/Indicator")
          : ParameterAcceptor(subsection)
          , hyperbolic_system_(&hyperbolic_system)
      {
        evc_factor_ = ScalarNumber(1.);
        add_parameter("evc factor",
                      evc_factor_,
                      "Factor for scaling the entropy viscocity commuator");
      }
 
 
 
      ACCESSOR_READ_ONLY(evc_factor);
 
      template <int dim, typename Number>
      auto view() const
      {
        return View<dim, Number>{
            hyperbolic_system_->template view<dim, Number>(), *this};
      }
 
    private:
 
 
      ScalarNumber evc_factor_;
 
 
 
      dealii::ObserverPointer<const HyperbolicSystem> hyperbolic_system_;
 
    };
 
 
    template <int dim, typename Number>
    class IndicatorView
    {
    public:
 
      using View = HyperbolicSystemView<dim, Number>;
 
      using ScalarNumber = typename View::ScalarNumber;
 
      static constexpr auto problem_dimension = View::problem_dimension;
 
      using state_type = typename View::state_type;
 
      using flux_type = typename View::flux_type;
 
      using precomputed_type = typename View::precomputed_type;
 
      using PrecomputedVectorView = typename View::PrecomputedVectorView;
 
 
 
      IndicatorView(const View &view, const Indicator<ScalarNumber> &indicator)
          : view_(view)
          , indicator_(indicator)
      {
      }
 
      void reset(const PrecomputedVectorView &pv,
                 const unsigned int i,
                 const state_type &U_i);
 
      void accumulate(const PrecomputedVectorView &pv,
                      const unsigned int *js,
                      const state_type &U_j,
                      const dealii::Tensor<1, dim, Number> &c_ij);
 
      Number alpha(const Number h_i) const;
 
 
    private:
 
 
      const View view_;
      const Indicator<ScalarNumber> &indicator_;
 
      Number u_i_;
      Number u_abs_max_;
      dealii::Tensor<1, dim, Number> f_i_;
      Number left_;
      Number right_;
    };
 
 
    /*
     * -------------------------------------------------------------------------
     * Inline definitions
     * -------------------------------------------------------------------------
     */
 
 
    template <int dim, typename Number>
    DEAL_II_ALWAYS_INLINE inline void
    IndicatorView<dim, Number>::reset(const PrecomputedVectorView &pv,
                                      const unsigned int i,
                                      const state_type &U_i)
    {
      /* entropy viscosity commutator: */
 
      const auto prec_i = pv.template read_tensor<Number, precomputed_type>(i);
 
      u_i_ = view_.state(U_i);
      u_abs_max_ = std::abs(u_i_);
      f_i_ = view_.construct_flux_tensor(prec_i);
      left_ = 0.;
      right_ = 0.;
    }
 
 
    template <int dim, typename Number>
    DEAL_II_ALWAYS_INLINE inline void IndicatorView<dim, Number>::accumulate(
        const PrecomputedVectorView &pv,
        const unsigned int *js,
        const state_type &U_j,
        const dealii::Tensor<1, dim, Number> &c_ij)
    {
      /* entropy viscosity commutator: */
 
      const auto prec_j = pv.template read_tensor<Number, precomputed_type>(js);
 
      const auto u_j = view_.state(U_j);
      u_abs_max_ = std::max(u_abs_max_, std::abs(u_j));
      const auto d_eta_j = view_.kruzkov_entropy_derivative(u_i_, u_j);
      const auto f_j = view_.construct_flux_tensor(prec_j);
 
      left_ += d_eta_j * (f_j * c_ij);
      right_ += d_eta_j * (f_i_ * c_ij);
    }
 
 
    template <int dim, typename Number>
    DEAL_II_ALWAYS_INLINE inline Number
    IndicatorView<dim, Number>::alpha(const Number hd_i) const
    {
      Number numerator = left_ - right_;
      Number denominator = std::abs(left_) + std::abs(right_);
 
      const auto regularization =
          Number(100. * std::numeric_limits<ScalarNumber>::min());
 
      const auto quotient =
          std::abs(numerator) /
          (denominator + std::max(hd_i * std::abs(u_abs_max_), regularization));
 
      return std::min(Number(1.), indicator_.evc_factor() * quotient);
    }
 
  } // namespace ScalarConservation
} // namespace ryujin