kernel_density_estimation/kernel/
triweight.rs

1//! Triweight kernel function.
2
3use crate::float::{float, KDEFloat};
4use crate::kernel::Kernel;
5
6/// Triweight kernel function.
7#[derive(Clone, Copy, Debug)]
8pub struct Triweight;
9
10impl<F: KDEFloat> Kernel<F> for Triweight {
11    fn pdf(&self, x: F) -> F {
12        let abs_x = x.abs();
13        if abs_x <= F::one() {
14            float!(35.0 / 32.0) * (F::one() - x.powi(2)).powi(3)
15        } else {
16            F::zero()
17        }
18    }
19}
20
21#[cfg(test)]
22mod tests {
23    use super::Triweight;
24    use crate::kernel::Kernel;
25    use approx::*;
26
27    #[test]
28    fn triweight() {
29        let kernel = Triweight;
30
31        let x = 0.0;
32        let res = kernel.pdf(x);
33        assert_relative_eq!(res, 1.09375, epsilon = 1.0e-5);
34
35        let x = -1.0;
36        let res = kernel.pdf(x);
37        assert_relative_eq!(res, 0.0, epsilon = 1.0e-5);
38
39        let x = 1.0;
40        let res = kernel.pdf(x);
41        assert_relative_eq!(res, 0.0, epsilon = 1.0e-5);
42
43        let x = 0.5;
44        let res = kernel.pdf(x);
45        assert_relative_eq!(res, 0.46143, epsilon = 1.0e-5);
46    }
47}