[simonreiff]

I really recommend Professor Gilbert Strang's linear algebra course and also would check out any Michael Penn videos, both on YouTube, but for linear algebra, the Strang/MIT course is the best resource anywhere that I know. The Gilbert Strang video series on linear algebra includes the 18.06 course, as well as an 18.06B or something like that where he goes into detail about the SVD and ML algorithms like gradient descent.

Generally if you're struggling with a math paper on the first or second page, no point in fighting it; gotta come back after you have the prerequisites. Nobody is born knowing this stuff, and also, all branches of math contain endless piles of really easy-to-describe but hopelessly difficult problems so never feel bad if you don't know how to solve a problem or even understand what you are reading. Just take your time, learn what you need, come back, a bit more hopefully makes sense, learn still more, and over time more things will become familiar.