Function cv_fdata 

pub fn cv_fdata<F, P>(
    data: &FdMatrix,
    y: &[f64],
    fit_fn: F,
    predict_fn: P,
    n_folds: usize,
    nrep: usize,
    cv_type: CvType,
    stratified: bool,
    seed: u64,
) -> CvFdataResult
where
    F: Fn(&FdMatrix, &[f64]) -> Box<dyn Any>,
    P: Fn(&dyn Any, &FdMatrix) -> Vec<f64>,

Generic k-fold + repeated cross-validation framework (R’s cv.fdata).