In this lecture, I have no idea what i denotes in forloop. Please help me, thank you.
What happens is that you “unroll” all the parameters (all the W matrices and all the b vectors) into a single vector which Prof Ng labels \theta. Then you loop over all the elements in that \theta vector. It’s been a while since I listened to that lecture, so I forget exactly what Prof Ng says, but he must have explained that. I suggest you “rewind” and watch that section again with what I said above in mind and it all should make more sense.
I understand , thank you so much!