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math_audio_test_functions/functions/
brown.rs

1//! Brown test function
2
3use ndarray::Array1;
4
5/// Brown function - ill-conditioned unimodal function
6/// Global minimum: f(x) = 0 at x = (0, 0, ..., 0)
7/// Bounds: x_i in [-1, 4]
8pub fn brown(x: &Array1<f64>) -> f64 {
9    let mut sum = 0.0;
10    for i in 0..x.len() - 1 {
11        let xi = x[i];
12        let xi_plus_1 = x[i + 1];
13        sum += (xi.powi(2)).powf(xi_plus_1.powi(2) + 1.0);
14        sum += (xi_plus_1.powi(2)).powf(xi.powi(2) + 1.0);
15    }
16    sum
17}