Confusion in FastPhysicsEngine.hpp where caculating drag force

[yizhendongfeng]

I'm reading code in FastPhysicsEngine.hpp and confused about the following code on line 363. Why the right part in the equation multiply 0.5f?

AirSim/AirLib/include/physics/FastPhysicsEngine.hpp

Lines 355 to 356 in 6688d27

	avg_linear = current.twist.linear + current.accelerations.linear * (0.5f * dt_real);
	avg_angular = current.twist.angular + current.accelerations.angular * (0.5f * dt_real);

[yizhendongfeng]

avg_linear is average speed! avg_linear = (current.twist.linear + (current.twist.linear + current.accelerations.linear * dt_real)) / 2