Then you might prefer my https://news.ycombinator.com/item?id=21301117 https://news.ycombinator.com/item?id=21301117 here. I carefully define all symbols. I

Then you might prefer my https://news.ycombinator.com/item?id=21301117 https://news.ycombinator.com/item?id=21301117 here. I carefully define all symbols. I keep the math really simple; the only prerequisite is matrix multiplication; don't need matrix inverse. For matrix transpose, I define that. For squared length of a vector, I define that, too. I don't use calculus, derivatives, or probability. I derive the normal equations in just two lines of matrix algebra.