The confusing transformation about rewards to rtgs.

[RZ-Q]

In the get_episode() function, the rewards have been turned into reward-to-gos, which is not describe in the paper.

for agent_trajectory in episode:
    rtgs = 0
    for i in reversed(range(len(agent_trajectory))):
        rtgs += agent_trajectory[i][3][0]
        agent_trajectory[i][3][0] = rtgs

return episode

Can you explain why should turn rewards to reward-to-go? Is this transformation applied for other baselines too? Sorry to bother you.