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 <ryujin/base/compile_time_options.h>
#include <ryujin/base/gpu.h>
#include <ryujin/base/observer_pointer.h>
#include <ryujin/base/simd.h>
#include <ryujin/linear_algebra/multicomponent_vector.h>
#include <ryujin/scalar_conservation/hyperbolic_system.h>
 
#include <deal.II/base/parameter_acceptor.h>
#include <deal.II/base/vectorization.h>
 
namespace ryujin
{
  namespace ScalarConservation
  {
    template <int dim,
              typename Number = double,
              typename MemorySpace = dealii::MemorySpace::Host>
    class IndicatorView;
 
    template <typename ScalarNumber = double>
    class Indicator : public dealii::ParameterAcceptor
    {
    public:
 
      struct Parameters {
        double evc_factor;
      };
 
 
 
      Indicator(const HyperbolicSystem &hyperbolic_system,
                const std::string &subsection = "/Indicator")
          : ParameterAcceptor(subsection)
          , parameters_("scalar_conservation_indicator_parameters",
                        TransferPolicy::implicit_transfers_host_resident)
          , hyperbolic_system_(&hyperbolic_system)
      {
        /* reference remains valid due to implicit_transfers_host_resident */
        auto &parameters = *parameters_.view();
 
        parameters.evc_factor = 1.;
        add_parameter("evc factor",
                      parameters.evc_factor,
                      "Factor for scaling the entropy viscocity commuator");
 
        /* invalidates view on default memory space */
        ParameterAcceptor::parse_parameters_call_back.connect(
            [this] { parameters_.view(); });
      }
 
      template <int dim,
                typename Number,
                typename MemorySpace = dealii::MemorySpace::Host>
      auto view() const
      {
        return IndicatorView<dim, Number, MemorySpace>{
            hyperbolic_system_->template view<dim, Number, MemorySpace>(),
            *this};
      }
 
    private:
 
 
      Mirrored<Parameters> parameters_;
 
 
 
      dealii::ObserverPointer<const HyperbolicSystem> hyperbolic_system_;
 
      template <int, typename, typename>
      friend class IndicatorView;
 
    };
 
 
    template <int dim, typename Number, typename MemorySpace>
    class IndicatorView
    {
    public:
      static_assert(
          std::is_same_v<MemorySpace, dealii::MemorySpace::Host> ||
              std::is_same_v<MemorySpace, dealii::MemorySpace::Default>,
          "Unexpected memory space");
 
 
      using View = HyperbolicSystemView<dim, Number, MemorySpace>;
 
      using ScalarNumber = typename View::ScalarNumber;
 
      using state_type = typename View::state_type;
 
      using flux_contribution_type = typename View::flux_contribution_type;
 
      using precomputed_type = typename View::precomputed_type;
 
      using PrecomputedVectorView = typename View::PrecomputedVectorView;
 
 
 
      IndicatorView(const View &view, const Indicator<ScalarNumber> &indicator)
          : view_(view)
          , parameters_(indicator.parameters_.template view<MemorySpace>())
      {
      }
 
      DEAL_II_HOST_DEVICE_ALWAYS_INLINE ScalarNumber evc_factor() const
      {
        return ScalarNumber(parameters_->evc_factor);
      }
 
      DEAL_II_HOST_DEVICE void reset(const PrecomputedVectorView &pv,
                                     const unsigned int i,
                                     const state_type &U_i,
                                     const flux_contribution_type &flux_i);
 
      DEAL_II_HOST_DEVICE 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> &c_ij);
 
      DEAL_II_HOST_DEVICE Number alpha(const Number h_i) const;
 
 
    private:
 
 
      const View view_;
      const Indicator<ScalarNumber>::Parameters *const parameters_;
 
      Number u_i_ = 0.;
      Number u_abs_max_ = 0.;
      dealii::Tensor<1, dim, Number> f_i_;
      Number left_ = 0.;
      Number right_ = 0.;
    };
 
 
    /*
     * -------------------------------------------------------------------------
     * Inline definitions
     * -------------------------------------------------------------------------
     */
 
 
    template <int dim, typename Number, typename MemorySpace>
    DEAL_II_HOST_DEVICE_ALWAYS_INLINE void
    IndicatorView<dim, Number, MemorySpace>::reset(
        const PrecomputedVectorView &pv,
        const unsigned int i,
        const state_type &U_i,
        const flux_contribution_type & /*flux_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, typename MemorySpace>
    DEAL_II_HOST_DEVICE_ALWAYS_INLINE void
    IndicatorView<dim, Number, MemorySpace>::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> &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, typename MemorySpace>
    DEAL_II_HOST_DEVICE_ALWAYS_INLINE Number
    IndicatorView<dim, Number, MemorySpace>::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.), evc_factor() * quotient);
    }
 
  } // namespace ScalarConservation
} // namespace ryujin