> Depending on which convention you pick (column major and post-multiply or row major and pre-multiply) keep in mind it’ll be faster to return a matrix column i

> Depending on which convention you pick (column major and post-multiply or row major and pre-multiply) keep in mind it’ll be faster to return a matrix column if you’re using column major as we don’t have to construct a new object (we could if we wanted return a const reference to it). This seems kinda like the crux of the post, after describing in detail the various layouts and access patterns. There isn't much in the way of low level optimization and performance discussion here unfortunately.