#ifndef INCLUDE_ONCE_VECTOR_FIELD_FORCED_DAMPED_DUFFING_2D
#define INCLUDE_ONCE_VECTOR_FIELD_FORCED_DAMPED_DUFFING_2D

#include <cmath>
#include <algorithm>

typedef std::pair<double, double> Vec2d;

class forceddampedduffing2d
{
public:
	forceddampedduffing2d(double Alpha = -0.25, double Beta = 0.4) : alpha(Alpha), beta(Beta) {}

	// Samples the phase space vector field of the forced damped duffing oscillator
	Vec2d sample(double x, double y, double t)
	{
		return Vec2d(
			y,
			alpha * y - x * x*x + x + beta * std::cos(t));
	}

	// Samples the phase space x-partial of the vector field of the forced damped duffing oscillator
	Vec2d sample_dx(double x, double y, double t)
	{
		return Vec2d(
			0,
			1 - 3 * x*x);
	}

	// Samples the phase space y-partial of the vector field of the forced damped duffing oscillator
	Vec2d sample_dy(double x, double y, double t)
	{
		return Vec2d(
			1,
			alpha);
	}

	// Samples the phase space t-partial of the vector field of the forced damped duffing oscillator
	Vec2d sample_dt(double x, double y, double t)
	{
		return Vec2d(
			0,
			-beta * std::sin(t));
	}

private:
	double alpha;
	double beta;
};

#endif