wave_speed_estimator.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 <gpu.h>
#include <observer_pointer.h>
#include <simd.h>
 
#include <deal.II/base/point.h>
#include <deal.II/base/tensor.h>
 
// #define DEBUG_WAVE_SPEED_ESTIMATOR
 
namespace ryujin
{
  namespace EulerBarotropic
  {
    template <int dim,
              typename Number = double,
              typename MemorySpace = dealii::MemorySpace::Host>
    class WaveSpeedEstimatorView;
 
    template <typename ScalarNumber = double>
    class WaveSpeedEstimator : public dealii::ParameterAcceptor
    {
    public:
 
      WaveSpeedEstimator(const HyperbolicSystem &hyperbolic_system,
                         const std::string &subsection = "/WaveSpeedEstimator")
          : ParameterAcceptor(subsection)
          , hyperbolic_system_(&hyperbolic_system)
      {
      }
 
      template <int dim,
                typename Number,
                typename MemorySpace = dealii::MemorySpace::Host>
      auto view() const
      {
        return WaveSpeedEstimatorView<dim, Number, MemorySpace>{
            hyperbolic_system_->template view<dim, Number, MemorySpace>(),
            *this};
      }
 
    private:
 
 
      dealii::ObserverPointer<const HyperbolicSystem> hyperbolic_system_;
 
      template <int, typename, typename>
      friend class WaveSpeedEstimatorView;
 
    };
 
 
    template <int dim, typename Number, typename MemorySpace>
    class WaveSpeedEstimatorView
    {
    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;
 
      static constexpr unsigned int riemann_data_size = 2;
 
      using primitive_type = typename std::array<Number, riemann_data_size>;
 
      using precomputed_type = typename View::precomputed_type;
 
      using PrecomputedVectorView = typename View::PrecomputedVectorView;
 
 
 
      WaveSpeedEstimatorView(const View &view,
                             const WaveSpeedEstimator<ScalarNumber> & /*wse*/)
          : view_(view)
      {
      }
 
      DEAL_II_HOST_DEVICE Number
      compute(const primitive_type &riemann_data_i,
              const primitive_type &riemann_data_j) const;
 
      DEAL_II_HOST_DEVICE Number
      compute(const PrecomputedVectorView &pv,
              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 View view_;
 
    };
 
 
    /*
     * -------------------------------------------------------------------------
     * Inline definitions
     * -------------------------------------------------------------------------
     */
 
 
    template <int dim, typename Number, typename MemorySpace>
    DEAL_II_HOST_DEVICE_ALWAYS_INLINE Number
    WaveSpeedEstimatorView<dim, Number, MemorySpace>::compute(
        const primitive_type &riemann_data_i,
        const primitive_type &riemann_data_j) const
    {
      const auto &[u_i, a_i] = riemann_data_i;
      const auto &[u_j, a_j] = riemann_data_j;
 
#ifdef DEBUG_WAVE_SPEED_ESTIMATOR
      std::cout << "u_left: " << u_i << std::endl;
      std::cout << "a_left: " << a_i << std::endl;
      std::cout << "u_right: " << u_j << std::endl;
      std::cout << "a_right: " << a_j << std::endl;
#endif
 
      const Number lambda_max =
          std::max(std::abs(u_i) + a_i, std::abs(u_j) + a_j);
      return lambda_max;
    }
 
 
    template <int dim, typename Number, typename MemorySpace>
    DEAL_II_HOST_DEVICE_ALWAYS_INLINE Number
    WaveSpeedEstimatorView<dim, Number, MemorySpace>::compute(
        const PrecomputedVectorView &pv,
        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
    {
      const auto &[e_i, p_i, a_i] =
          pv.template read_tensor<Number, precomputed_type>(i);
 
      const auto &[e_j, p_j, a_j] =
          pv.template read_tensor<Number, precomputed_type>(js);
 
      const auto rho_i = view_.density(U_i);
      const auto rho_i_inverse = Number(1.0) / rho_i;
      const auto m_i = view_.momentum(U_i);
      const auto u_i = rho_i_inverse * n_ij * m_i;
 
      const auto rho_j = view_.density(U_j);
      const auto rho_j_inverse = Number(1.0) / rho_j;
      const auto m_j = view_.momentum(U_j);
      const auto u_j = rho_j_inverse * n_ij * m_j;
 
      return compute(primitive_type{u_i, a_i}, primitive_type{u_j, a_j});
    }
  } // namespace EulerBarotropic
} // namespace ryujin