merge stuff demo 2

Simulations/MassSpringSystemSimulator.h

@@ -38,6 +38,11 @@ public:
 	Vec3 getPositionOfMassPoint(int index);
 	Vec3 getVelocityOfMassPoint(int index);
 	void applyExternalForce(Vec3 force);
+
+	Vec3 calcualtePositionTimestepEuler(Vec3 oldPosition, float timestep, Vec3 veloctiy);
+	Vec3 calcualteVelocityTimestepEuler(Vec3 oldVelocity, float timestep, Vec3 acceleration);
+	Vec3 calculateAcceleration(Vec3 acceleration, float mass);
+	void Euler(int index1, int index2, int indexSpring, float timestep);
 	
 	// Do Not Change
 	void setIntegrator(int integrator) {