barotropic_equation_of_state_function.h

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//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Copyright (C) 2025 - 2026 by the ryujin authors
//
 
#pragma once
 
#include <ryujin/base/compile_time_options.h>
#include <ryujin/euler_barotropic/barotropic_equation_of_state.h>
 
#include <deal.II/base/function_parser.h>
 
namespace ryujin
{
  namespace BarotropicEquationsOfState
  {
    class Function : public BarotropicEquationOfState
    {
    public:
      Function(const std::string &subsection)
          : BarotropicEquationOfState("function", subsection)
      {
        sie_expression_ = "4. * ln(rho)";
        add_parameter("specific internal energy",
                      sie_expression_,
                      "A function expression for the specific internal energy "
                      "as a function of density: e(rho)");
 
        p_expression_ = "4. * rho";
        add_parameter("pressure",
                      p_expression_,
                      "A function expression for the pressure as a function of "
                      "density: p(rho)");
 
        sos_expression_ = "2.";
        add_parameter("speed of sound",
                      sos_expression_,
                      "A function expression for the speed of sound as a "
                      "function of density: a(rho)");
 
        /*
         * Set up the muparser object with the final equation of state
         * description from the parameter file:
         */
        const auto set_up_muparser = [this] {
          sie_function_ = std::make_unique<dealii::FunctionParser<1>>();
          sie_function_->initialize("rho", sie_expression_, {});
 
          p_function_ = std::make_unique<dealii::FunctionParser<1>>();
          p_function_->initialize("rho", p_expression_, {});
 
          sos_function_ = std::make_unique<dealii::FunctionParser<1>>();
          sos_function_->initialize("rho", sos_expression_, {});
        };
 
        set_up_muparser();
        ParameterAcceptor::parse_parameters_call_back.connect(set_up_muparser);
      }
 
      double specific_internal_energy(double rho) const final
      {
        return sie_function_->value(dealii::Point<1>(rho));
      }
 
      double pressure(double rho) const final
      {
        return p_function_->value(dealii::Point<1>(rho));
      }
 
      double speed_of_sound(double rho) const final
      {
        return sos_function_->value(dealii::Point<1>(rho));
      }
 
    private:
      std::string sie_expression_;
      std::string p_expression_;
      std::string sos_expression_;
 
      std::unique_ptr<dealii::FunctionParser<1>> sie_function_;
      std::unique_ptr<dealii::FunctionParser<1>> p_function_;
      std::unique_ptr<dealii::FunctionParser<1>> sos_function_;
    };
  } // namespace BarotropicEquationsOfState
} // namespace ryujin