RK4.hh

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/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *\
 * Copyright (c) 2025, Davide Stocco and Enrico Bertolazzi.                                      *
 *                                                                                               *
 * The Sandals project is distributed under the BSD 2-Clause License.                            *
 *                                                                                               *
 * Davide Stocco                                                               Enrico Bertolazzi *
 * University of Trento                                                     University of Trento *
 * e-mail: davide.stocco@unitn.it                             e-mail: enrico.bertolazzi@unitn.it *
\* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 
#pragma once
 
#ifndef SANDALS_RK4_HH
#define SANDALS_RK4_HH
 
#include <Sandals.hh>
#include <Sandals/RungeKutta.hh>
 
namespace Sandals
{
  template <typename Real>
  class RK4Tableau : public Tableau<Real, 4>
  {
  public:
    using typename Tableau<Real, 4>::Type;
    using typename Tableau<Real, 4>::Vector;
    using typename Tableau<Real, 4>::Matrix;

    RK4Tableau<Real>() {
      this->name  = "RK4";
      this->type  = Type::ERK;
      this->order = 4;
      this->A << 0.0,     0.0,     0.0,     0.0,
                 1.0/2.0, 0.0,     0.0,     0.0,
                 0.0,     1.0/2.0, 0.0,     0.0,
                 0.0,     0.0,     1.0,     0.0;
      this->b << 1.0/6.0, 1.0/3.0, 1.0/3.0, 1.0/6.0;
      this->c << 0.0,     1.0/2.0, 1.0/2.0, 1.0;
    }
  }; // class RK4Tableau

  template <typename Real, Integer N, Integer M = 0>
  class RK4 : public RungeKutta<Real, 4, N, M>
  {
  public:
    using System = typename Implicit<Real, N, M>::Pointer; 

    RK4() : RungeKutta<Real, 4, N, M>(RK4Tableau<Real>()) {}

    RK4(System t_system) : RungeKutta<Real, 4, N, M>(RK4Tableau<Real>(), t_system) {}
 
  }; // class RK4
 
} // namespace Sandals
 
#endif // SANDALS_RK4_HH