IT WORKS! But small difference between this version and the python. 46.2% vs 47.1%, but that's not much.

src/fitter.rs

@@ -10,6 +10,8 @@ pub trait Fitter {
 
     fn fit(&mut self);
 
+    fn predict(&self, ts: &[f64]) -> (Vec<f64>, Vec<f64>);
+
     fn vs(&self, idx: usize) -> f64;
     fn vs_mut(&mut self, idx: usize) -> &mut f64;