SimulatedAnnealing

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struct State{ // Structure representing the state
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  double x;
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  // f(x) = -x^4 + x^3 + x^2 + x
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  // max f(x): 2.33.... (x = 1.28...)
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  double eval(){ // Evaluation function
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    return -pow(x,4)+pow(x,3)+pow(x,2)+x;
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  }
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  void modify(){ // State transition
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    x += ((double)rand() / (RAND_MAX))-0.5;
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  }
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};
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ESAnnealing<State> sa;
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// Initialize the state inside sa
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sa.state.x=0;

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// (trials per epoch, initial temperature, target temperature, cooling coefficient)
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sa.annealing(100,100000,0.1,0.99);

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// The result can be referenced by 'state' in the class
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std::cout << "Solution: " << "f(x) = " << sa.state.eval() << ", x = " << sa.state.x << std::endl;

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template <class T>
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class ESAnnealing
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{
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public:
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  T state;
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  void annealing(double epoch, double temperature, double temperature_target, double coolingcoef, unsigned int seed = 42, bool verbose = true)
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  {
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    assert(0 <= coolingcoef and coolingcoef < 1);
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    assert(temperature >= temperature_target);
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    srand(seed);
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    double initscore = state.eval();
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    double beststate_score = initscore;
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    T beststate = state;
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    int estimeted_epoch = std::ceil((std::log(temperature_target) - std::log(temperature)) / std::log(coolingcoef));
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    if (verbose)
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      std::cout << std::fixed << std::setprecision(6)
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                << "ESAnnealing started with:" << "\n"
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                << "| epoch       " << epoch << "\n"
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                << "| temperature " << temperature << "\n"
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                << "| target temp " << temperature_target << "\n"
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                << "| coolingcoef " << coolingcoef << "\n"
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                << "| seed        " << seed << "\n"
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                << "| est epoch   " << estimeted_epoch << "\n"
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                << std::flush;
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    int cnt = 0;
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    while (temperature > temperature_target)
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    {
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      for (int i = 0; i < epoch; i++)
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      {
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        T newstate = state;
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        newstate.modify();
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        double statescore = state.eval();
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        double newstatescore = newstate.eval();
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        double delta = newstatescore - statescore;
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        if (0 < delta)
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        {
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          state = newstate;
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        }
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        else if (frand() > std::exp(delta / temperature))
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        {
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          state = newstate;
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        }
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        if (beststate_score < newstatescore)
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        {
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          beststate_score = newstatescore;
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          beststate = newstate;
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        }
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      }
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      temperature *= coolingcoef;
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      if (verbose)
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        std::cout << cnt << "/" << estimeted_epoch - 1 << " temp: " << temperature << " eval: " << beststate_score << std::endl;
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      cnt++;
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    }
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    state = beststate;
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    if (verbose)
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      std::cout << "annealed: " << initscore << "->" << beststate_score << std::endl;
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  }
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private:
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  double frand()
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  {
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    return ((double)rand() / (RAND_MAX));
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  }
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};