Why the value loss need to devide 2 in line 108 of a3c.py

[onlytailei]

v_loss += (v - R) ** 2 / 2

But the original paper just calculate the derivative of the (V-R)^2 right?

[onlytailei]

And you mentioned in https://github.com/muupan/async-rl/wiki
They multiply the gradients of V by 0.5. So in the a3c.py there are the parameters (pi_loss_coef=1.0, v_loss_coef=0.5)
But why there is another 0.5 in v_loss?