Line data    Source code

       1            0 : // Distributed under the MIT License.
       2              : // See LICENSE.txt for details.
       3              : 
       4              : #pragma once
       5              : 
       6              : #include <cstddef>
       7              : 
       8              : #include "DataStructures/TaggedVariant.hpp"
       9              : #include "Options/String.hpp"
      10              : #include "Time/TimeSteppers/ImexRungeKutta.hpp"
      11              : #include "Utilities/Serialization/CharmPupable.hpp"
      12              : #include "Utilities/TMPL.hpp"
      13              : 
      14              : namespace TimeSteppers {
      15              : /*!
      16              :  * \ingroup TimeSteppersGroup
      17              :  * \brief A third-order Runge-Kutta method with IMEX support.
      18              :  *
      19              :  * The method as published has four stages, but is implemented with
      20              :  * five as a way to convert it to an EDIRK method.
      21              :  *
      22              :  * The coefficients are given as IMEX-SSP3(4,3,3) in \cite Pareschi2005.
      23              :  *
      24              :  * While this method can be implemented so that the explicit part is
      25              :  * strong-stability-preserving, the presentation in \cite Pareschi2005
      26              :  * is not, and this implementation follows that presentation.  See
      27              :  * \cite HesthavenWarburton section 5.7 for details.
      28              :  *
      29              :  * Using this time stepper in a non-IMEX simulation is not
      30              :  * recommended, as it performs two unused RHS evaluations.  When using
      31              :  * IMEX it performs one extra evaluation because there are more
      32              :  * implicit steps than explicit.
      33              :  *
      34              :  * The implicit portion is L-stable.
      35              :  *
      36              :  * The CFL factor/stable step size is 1.25637.
      37              :  */
      38            1 : class Rk3Pareschi : public ImexRungeKutta {
      39              :  public:
      40            0 :   using options = tmpl::list<>;
      41            0 :   static constexpr Options::String help = {
      42              :       "A 3rd-order 4 stage Runge-Kutta scheme devised by Pareschi and Russo."};
      43              : 
      44            0 :   Rk3Pareschi() = default;
      45            0 :   Rk3Pareschi(const Rk3Pareschi&) = default;
      46            0 :   Rk3Pareschi& operator=(const Rk3Pareschi&) = default;
      47            0 :   Rk3Pareschi(Rk3Pareschi&&) = default;
      48            0 :   Rk3Pareschi& operator=(Rk3Pareschi&&) = default;
      49            0 :   ~Rk3Pareschi() override = default;
      50              : 
      51            1 :   variants::TaggedVariant<Tags::FixedOrder, Tags::VariableOrder> order()
      52              :       const override;
      53              : 
      54            1 :   double stable_step() const override;
      55              : 
      56            1 :   size_t imex_order() const override;
      57              : 
      58            1 :   size_t implicit_stage_order() const override;
      59              : 
      60            0 :   WRAPPED_PUPable_decl_template(Rk3Pareschi);  // NOLINT
      61              : 
      62            0 :   explicit Rk3Pareschi(CkMigrateMessage* /*unused*/) {}
      63              : 
      64            0 :   const ButcherTableau& butcher_tableau() const override;
      65              : 
      66            0 :   const ImplicitButcherTableau& implicit_butcher_tableau() const override;
      67              : };
      68              : 
      69            0 : inline bool constexpr operator==(const Rk3Pareschi& /*lhs*/,
      70              :                                  const Rk3Pareschi& /*rhs*/) {
      71              :   return true;
      72              : }
      73              : 
      74            0 : inline bool constexpr operator!=(const Rk3Pareschi& lhs,
      75              :                                  const Rk3Pareschi& rhs) {
      76              :   return not(lhs == rhs);
      77              : }
      78              : }  // namespace TimeSteppers