Meaning of summation variables i and j

I have a question, this is picture from the word2vec video, what do j and i represent?

We can look at the summation signs to see they both go from 1 to 10,000, and 10,000 is the vocab size, so they are both the vocab index.

They can also be called as “dummy variables”. We could have used the same symbol but it is fine too to use i here and j there.

@Namhoang, I split this into a new thread for you, but next time, please open a new thread for a different question.