Python Double Colon (::) Syntax

collection[start:stop:step]

Also, from: https://d2l.ai/chapter_preliminaries/ndarray.html

• This algorithm ensures that weights are non-negative,
• and that they sum up to 1.
• It's a normalization algorithm

From: https://en.wikipedia.org/wiki/Dot_product

dot product is a measure of similarity of two vectors. It is a single number.