solver.cpp

bool exit_status = cranberries::make_rkf45(
    // Lorenz attractor
    [&,p = 10.L,r = 28.L,b = 8.L/3](const long double t, const state_type& x) {
    state_type dxdt{};
    // x=x[0], y=x[1], z=x[2]
    dxdt[0] = -p*x[0] + p*x[1];              // dx/dt
    dxdt[1] = -x[0] * x[2] + r*x[0] - x[1];  // dy/dt
    dxdt[2] = x[0] * x[1] - b*x[2];          // dz/dt
    return dxdt;
  })
  .set_integrate_range({ 0,25 })
  .set_tolerance(8.0E-3L)
  .set_step_size_range({ 1.0E-6,0.05 })
  .integrate(state0,
      [&](auto t, state_type state){
      std::cout
        << "t=" << t << " "
        << "x=" << state[0] << " "
        << "y=" << state[1] << " "
        << "z=" << state[2] << "\n";
  });