The quality of the course seems to have gone downhill with this exercise:

Typo and strange explanations.

A) There’s a typo in equation 1. It says x^<t+1> where it should be x^.

B)Furthermore, the wrap-around issue for the indexing in exercise 3 is poorly explained. I have no idea what " Set the index idx into the list of examples" could mean.

There is a list of examples, a different one of which is used as an input on each iteration of the loop. You index the list with the iteration number using the usual python syntax, but you need to be cognizant of the fact that the number of iterations is arbitrary, so it might potentially be larger than the length of the list of examples. They are explaining to you how you need to handle that.

Equation one is correct. At each timestep, you take the a from the previous timestep, together with the x for the current timestep and create the a and y for the current timestep, which is t + 1 the way they notated it. So t is the previous timestep and a^{<t>} is what they call a_prev when they are using python variable names.

Thank you very much. I meant to say that I finally understood and did the assignment , but still didn’t understand what that sentence really meant. You’re right about Equation 1, but hopefully this will help others with Ex. 3.