// Copyright (c) 2010-2020, Lawrence Livermore National Security, LLC. Produced
// at the Lawrence Livermore National Laboratory. All Rights reserved. See files
// LICENSE and NOTICE for details. LLNL-CODE-806117.
//
// This file is part of the MFEM library. For more information and source code
// availability visit https://mfem.org.
//
// MFEM is free software; you can redistribute it and/or modify it under the
// terms of the BSD-3 license. We welcome feedback and contributions, see file
// CONTRIBUTING.md for details.

#include "mfem.hpp"
#include "catch.hpp"
#include <cmath>

using namespace mfem;

TEST_CASE("First order ODE methods",
          "[ODE1]")
{
   double tol = 0.1;

   // Class for simple linear first order ODE.
   //    du/dt  + a u = 0
   class ODE : public TimeDependentOperator
   {
   protected:
      DenseMatrix A,I,T;
      Vector r;
   public:
      ODE(double a00,double a01,double a10,double a11) : TimeDependentOperator(2, 0.0)
      {
         A.SetSize(2,2);
         I.SetSize(2,2);
         T.SetSize(2,2);
         r.SetSize(2);

         A(0,0) = a00;
         A(0,1) = a01;
         A(1,0) = a10;
         A(1,1) = a11;

         I =  0.0;
         I(0,0) = I(1,1) = 1.0;
      };

      virtual void Mult(const Vector &u, Vector &dudt)  const
      {
         A.Mult(u,dudt);
         dudt.Neg();
      }

      virtual void ImplicitSolve(const double dt, const Vector &u, Vector &dudt)
      {
         // Residual
         A.Mult(u,r);
         r.Neg();

         // Jacobian
         Add(I,A,dt,T);

         // Solve
         T.Invert();

         T.Mult(r,dudt);
      }

      virtual ~ODE() {};
   };

   // Class for checking order of convergence of first order ODE.
   class CheckODE
   {
   protected:
      int ti_steps,levels;
      Vector u0;
      double t_final,dt;
      ODE *oper;
   public:
      CheckODE()
      {
         oper = new ODE(0.0, 1.0, -1.0, 0.0);
         ti_steps = 2;
         levels   = 6;

         u0.SetSize(2);
         u0    = 1.0;

         t_final = M_PI;
         dt = t_final/double(ti_steps);
      };

      double order(ODESolver* ode_solver)
      {
         double dt,t;
         Vector u(2);
         Vector err(levels);
         int steps = ti_steps;

         t = 0.0;
         dt = t_final/double(steps);
         u = u0;
         ode_solver->Init(*oper);
         for (int ti = 0; ti< steps; ti++)
         {
            ode_solver->Step(u, t, dt);
         }
         u +=u0;
         err[0] = u.Norml2();

         std::cout<<std::setw(12)<<"Error"
                  <<std::setw(12)<<"Ratio"
                  <<std::setw(12)<<"Order"<<std::endl;
         std::cout<<std::setw(12)<<err[0]<<std::endl;

         for (int l = 1; l< levels; l++)
         {
            t = 0.0;
            steps *=2;
            dt = t_final/double(steps);
            u = u0;
            ode_solver->Init(*oper);
            for (int ti = 0; ti< steps; ti++)
            {
               ode_solver->Step(u, t, dt);
            }
            u +=u0;
            err[l] = u.Norml2();
            std::cout<<std::setw(12)<<err[l]
                     <<std::setw(12)<<err[l-1]/err[l]
                     <<std::setw(12)<<log(err[l-1]/err[l])/log(2) <<std::endl;
         }
         delete ode_solver;

         return log(err[levels-2]/err[levels-1])/log(2);
      }
      virtual ~CheckODE() {delete oper;};
   };
   CheckODE check;

   // Implicit L-stable methods
   SECTION("BackwardEuler")
   {
      std::cout <<"\nTesting BackwardEuler" << std::endl;
      REQUIRE(check.order(new BackwardEulerSolver) + tol > 1.0 );
   }

   SECTION("SDIRK23Solver(2)")
   {
      std::cout <<"\nTesting SDIRK23Solver(2)" << std::endl;
      REQUIRE(check.order(new SDIRK23Solver(2)) + tol > 2.0 );
   }

   SECTION("SDIRK33Solver")
   {
      std::cout <<"\nTesting SDIRK33Solver" << std::endl;
      REQUIRE(check.order(new SDIRK33Solver) + tol > 3.0 );
   }

   SECTION("ForwardEulerSolver")
   {
      std::cout <<"\nTesting ForwardEulerSolver" << std::endl;
      REQUIRE(check.order(new ForwardEulerSolver) + tol > 1.0 );
   }

   SECTION("RK2Solver(0.5)")
   {
      std::cout <<"\nTesting RK2Solver(0.5)" << std::endl;
      REQUIRE(check.order(new RK2Solver(0.5))+ tol > 2.0 );
   }

   SECTION("RK3SSPSolver")
   {
      std::cout <<"\nTesting RK3SSPSolver" << std::endl;
      REQUIRE(check.order(new RK3SSPSolver) + tol > 3.0 );
   }

   SECTION("RK4Solver")
   {
      std::cout <<"\nTesting RK4Solver" << std::endl;
      REQUIRE(check.order(new RK4Solver) + tol > 4.0 );
   }

   SECTION("ImplicitMidpointSolver")
   {
      std::cout <<"\nTesting ImplicitMidpointSolver" << std::endl;
      REQUIRE(check.order(new ImplicitMidpointSolver) + tol > 2.0 );
   }

   SECTION("SDIRK23Solver")
   {
      std::cout <<"\nTesting SDIRK23Solver" << std::endl;
      REQUIRE(check.order(new SDIRK23Solver) + tol > 3.0 );
   }

   SECTION("SDIRK34Solver")
   {
      std::cout <<"\nTesting SDIRK34Solver" << std::endl;
      REQUIRE(check.order(new SDIRK34Solver) + tol > 4.0 );
   }

   // Generalized-alpha
   SECTION("GeneralizedAlphaSolver(1.0)")
   {
      std::cout <<"\nTesting GeneralizedAlphaSolver(1.0)" << std::endl;
      REQUIRE(check.order(new GeneralizedAlphaSolver(1.0)) + tol > 2.0 );
   }

   SECTION("GeneralizedAlphaSolver(0.5)")
   {
      std::cout <<"\nTesting GeneralizedAlphaSolver(0.5)" << std::endl;
      REQUIRE(check.order(new GeneralizedAlphaSolver(0.5)) + tol > 2.0 );
   }

   SECTION("GeneralizedAlphaSolver(0.0)")
   {
      std::cout <<"\nTesting GeneralizedAlphaSolver(0.0)" << std::endl;
      REQUIRE(check.order(new GeneralizedAlphaSolver(0.0)) + tol > 2.0 );
   }

   // Adams-Bashforth
   SECTION("AB1Solver()")
   {
      std::cout <<"\nTesting AB1Solver()" << std::endl;
      REQUIRE(check.order(new AB1Solver()) + tol > 1.0 );
   }

   SECTION("AB2Solver()")
   {
      std::cout <<"\nTesting AB2Solver()" << std::endl;
      REQUIRE(check.order(new AB2Solver()) + tol > 2.0 );
   }

   SECTION("AB3Solver()")
   {
      std::cout <<"\nTesting AB3Solver()" << std::endl;
      REQUIRE(check.order(new AB3Solver()) + tol > 3.0 );
   }

   SECTION("AB4Solver()")
   {
      std::cout <<"\nTesting AB4Solver()" << std::endl;
      REQUIRE(check.order(new AB4Solver()) + tol > 4.0 );
   }

   SECTION("AB5Solver(5)")
   {
      std::cout <<"\nTesting AB5Solver()" << std::endl;
      REQUIRE(check.order(new AB5Solver()) + tol > 5.0 );
   }

   // Adams-Moulton
   SECTION("AM0Solver()")
   {
      std::cout <<"\nTesting AM0Solver()" << std::endl;
      REQUIRE(check.order(new AM0Solver()) + tol > 1.0 );
   }

   SECTION("AM1Solver()")
   {
      std::cout <<"\nTesting AM1Solver()" << std::endl;
      REQUIRE(check.order(new AM1Solver()) + tol > 2.0 );
   }

   SECTION("AM2Solver()")
   {
      std::cout <<"\nTesting AM2Solver()" << std::endl;
      REQUIRE(check.order(new AM2Solver()) + tol > 3.0 );
   }

   SECTION("AM3Solver()")
   {
      std::cout <<"\nTesting AM3Solver()" << std::endl;
      REQUIRE(check.order(new AM3Solver()) + tol > 4.0 );
   }

   SECTION("AM4Solver()")
   {
      std::cout <<"\nTesting AM4Solver()" << std::endl;
      REQUIRE(check.order(new AM4Solver()) + tol > 5.0 );
   }
}