Question about the compute_lambda_values function

[zichunxx]

Hi! Thanks for your work on reimplementing dreamverv1 in a simple way.

I tried to learn the computation process of dreamerv1, but feel confused about the logistics of the compute_lambda_values function:

sheeprl/sheeprl/algos/dreamer_v1/utils.py

Lines 66 to 77 in dee8c80

	last_values = torch.clone(last_values)
	last_lambda_values = 0
	lambda_targets = []
	for step in reversed(range(horizon - 1)):
	if step == horizon - 2:
	next_values = last_values
	else:
	next_values = values[step + 1] * (1 - lmbda)
	delta = rewards[step] + next_values * done_mask[step]
	last_lambda_values = delta + lmbda * done_mask[step] * last_lambda_values
	lambda_targets.append(last_lambda_values)
	return torch.stack(list(reversed(lambda_targets)), dim=0)

1. Does the above snippet refer to Eq.6 in the original paper? i.e.,

$$V_\lambda(s_\lambda) = (1- \lambda) \sum_{n-1}^{H-1} \lambda ^{n-1} V_N^n(s_\lambda) + \lambda ^{H-1} V_N^H(s_\lambda)$$

I could not find anything in common between them.

2. If so, what does delta mean? Is delta TD target?

I'm new to the Dreamer series. Please forgive me if my question looks dumb to you. Thanks.

[zichunxx]

Update:

I think I have found the answer in Eq.4 of dreamerv2: