Thanks! Is this a fix for something that went wrong from 0.8.0 to 0.9.0 (the conversion from ndarray to nalgebra in this case) or something that was just not used so far? I'm a bit lost.

Yeah this basically broke when rewriting it from ndarray to nalgebra:

let m = (x * &self.params.m).sum(); // <--- was: (*) does matmul, not component_mul in nalgebra
let m = x.dot(&self.params.m); // <--- should be the dot product

Changing pref accordingly to a (row) vector (component multiplication) then requires transposing when calculating the coefficients.

We currently only test pure systems and hence this error was not caught.