hand-rolling ols regression in rust, and the collinearity trap that ate my coefficients

Mon, 27 Apr 2026 00:00:00 +0000

lights out, again.

last time out i argued that a chart is just rectangles and lines, drew stintlab’s entire ui in rust on canvas2d to prove it, and promised — right at the bottom of that post — to come back for the degradation model itself: the math the pictures are pictures of. this is that post.

the pictures draw a number. how much slower a tire gets, lap after lap, as it wears out. pin that number down and you can start to guess when a car should box. so i tried to fit it with a multiple linear regression i wrote by hand — no nalgebra, no ndarray, just the normal equations and a determinant — and the thing handed me back confident, well-formed garbage. it took a comment in one of my own tests to explain why.

math on krtffl.dev

hand-rolling ols regression in rust, and the collinearity trap that ate my coefficients