math-test-functions 0.5.2

A collection of non linear functions for testing optimisation algorithms
Documentation 
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//! Bird test function

use ndarray::Array1;

/// Bird function - 2D multimodal
/// Global minimum: f(x) = -106.764537 at x = (4.70104, 3.15294) and (-1.58214, -3.13024)
/// Bounds: x_i in [-2π, 2π]
pub fn bird(x: &Array1<f64>) -> f64 {
    let x1 = x[0];
    let x2 = x[1];
    let term1 = x1.sin() * ((1.0 - x2.cos()).powi(2)).exp();
    let term2 = x2.cos() * ((1.0 - x1.sin()).powi(2)).exp();
    let term3 = (x1 - x2).powi(2);
    term1 + term2 + term3
}