riemann_solver.h

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//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Copyright (C) 2023 - 2024 by the ryujin authors
//
 
#pragma once
 
#include "hyperbolic_system.h"
 
#include <simd.h>
 
#include <deal.II/base/point.h>
#include <deal.II/base/tensor.h>
 
namespace ryujin
{
  namespace ScalarConservation
  {
    template <typename ScalarNumber = double>
    class RiemannSolverParameters : public dealii::ParameterAcceptor
    {
    public:
      RiemannSolverParameters(const std::string &subsection = "/RiemannSolver")
          : ParameterAcceptor(subsection)
      {
        use_greedy_wavespeed_ = false;
        add_parameter("use greedy wavespeed",
                      use_greedy_wavespeed_,
                      "Use a greedy wavespeed estimate instead of a guaranteed "
                      "upper bound "
                      "on the maximal wavespeed (for convex fluxes).");
 
        use_averaged_entropy_ = false;
        add_parameter("use averaged entropy",
                      use_averaged_entropy_,
                      "In addition to the wavespeed estimate based on the Roe "
                      "average and "
                      "flux gradients of the left and right state also enforce "
                      "an entropy "
                      "inequality on the averaged Krŭzkov entropy.");
 
        random_entropies_ = 0;
        add_parameter(
            "random entropies",
            random_entropies_,
            "In addition to the wavespeed estimate based on the Roe average "
            "and "
            "flux gradients of the left and right state also enforce an "
            "entropy "
            "inequality on the prescribed number of random Krŭzkov entropies.");
      }
 
      ACCESSOR_READ_ONLY(use_greedy_wavespeed);
      ACCESSOR_READ_ONLY(use_averaged_entropy);
      ACCESSOR_READ_ONLY(random_entropies);
 
    private:
      bool use_greedy_wavespeed_;
      bool use_averaged_entropy_;
      unsigned int random_entropies_;
    };
 
 
    template <int dim, typename Number = double>
    class RiemannSolver
    {
    public:
      using View = HyperbolicSystemView<dim, Number>;
 
      using state_type = typename View::state_type;
 
      static constexpr unsigned int n_precomputed_values =
          View::n_precomputed_values;
 
      using precomputed_state_type = typename View::precomputed_state_type;
 
      using ScalarNumber = typename get_value_type<Number>::type;
 
      using Parameters = RiemannSolverParameters<ScalarNumber>;
 
 
      RiemannSolver(
          const HyperbolicSystem &hyperbolic_system,
          const Parameters &parameters,
          const MultiComponentVector<ScalarNumber, n_precomputed_values>
              &precomputed_values)
          : hyperbolic_system(hyperbolic_system)
          , parameters(parameters)
          , precomputed_values(precomputed_values)
      {
      }
 
      Number compute(const Number &u_i,
                     const Number &u_j,
                     const precomputed_state_type &prec_i,
                     const precomputed_state_type &prec_j,
                     const dealii::Tensor<1, dim, Number> &n_ij) const;
 
      Number compute(const state_type &U_i,
                     const state_type &U_j,
                     const unsigned int i,
                     const unsigned int *js,
                     const dealii::Tensor<1, dim, Number> &n_ij) const;
 
    private:
      const HyperbolicSystem &hyperbolic_system;
      const Parameters &parameters;
 
      const MultiComponentVector<ScalarNumber, n_precomputed_values>
          &precomputed_values;
    };
  } // namespace ScalarConservation
} // namespace ryujin