Function r2_indicator 

pub fn r2_indicator(
    approx_front: &[Vec<f64>],
    weight_vectors: &[Vec<f64>],
    reference_point: &[f64],
    utility: R2Utility,
) -> f64

R2 quality indicator.

Evaluates a Pareto front approximation using a set of reference weight vectors and a scalarizing utility function. Defined as:

R2(A, Λ, z*) = (1/|Λ|) Σ_{λ ∈ Λ} min_{a ∈ A} u(a | λ, z*)

A lower R2 value indicates a better approximation (closer to ideal).

Arguments

• approx_front - Approximation set to evaluate.
• weight_vectors - Reference weight vectors (each summing to ~1).
• reference_point - Ideal point z* (minimization target; typically the component-wise minimum of the true Pareto front).
• utility - Scalarizing function variant.

Returns

R2 value. Lower is better. Returns f64::INFINITY for empty inputs.

Examples

use scirs2_optimize::multiobjective::indicators::{r2_indicator, R2Utility};
let front = vec![vec![0.0,1.0], vec![0.5,0.5], vec![1.0,0.0]];
let weights = vec![vec![1.0,0.0], vec![0.5,0.5], vec![0.0,1.0]];
let z_star = vec![0.0, 0.0];
let r2 = r2_indicator(&front, &weights, &z_star, R2Utility::Tchebycheff);
assert!(r2 >= 0.0);