Function psi

pub fn psi(
    equation: &impl Equation,
    subjects: &Data,
    support_points: &ArrayBase<OwnedRepr<f64>, Dim<[usize; 2]>>,
    error_model: &ErrorModel<'_>,
    progress: bool,
    cache: bool,
) -> ArrayBase<OwnedRepr<f64>, Dim<[usize; 2]>>