Trait metaheuristics_nature::utility::Fitness

source · [−]
pub trait Fitness: Sync + Send + Default + Clone + PartialOrd { }
Expand description

The return value of the objective function (ObjFunc).

Usually, we can use numeric f64 / f32 type as the return value. But more advanced is that any type that implements the requirement trait can be used, so the fitness can add special mark during comparison (PartialOrd).

In the following example, an “important” marker has higher priority in the comparison.

use metaheuristics_nature::{utility::Fitness, ObjFunc};
use std::cmp::Ordering;

#[derive(Clone, PartialEq, Default)]
struct MarkerFitness {
    f: f64,
    important: bool,
}

impl PartialOrd for MarkerFitness {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        match (self.important, other.important) {
            (true, false) => Some(Ordering::Greater),
            (false, true) => Some(Ordering::Less),
            (false, false) | (true, true) => self.f.partial_cmp(&other.f),
        }
    }
}

impl ObjFunc for MyFunc {
    type Result = f64;
    type Fitness = MarkerFitness;

    fn fitness(&self, v: &[f64], f: f64) -> Self::Fitness {
        MarkerFitness {
            f: v[0],
            important: v[0] + v[1] * f < 1.,
        }
    }

    fn result(&self, v: &[f64]) -> Self::Result {
        self.fitness(v, 0.).f
    }

    fn ub(&self) -> &[f64] {
        &self.1
    }

    fn lb(&self) -> &[f64] {
        &self.0
    }
}

Implementors