roma_lib 0.1.1

A Rust metaheuristics framework inspired by jMetal for optimization and experimentation.
Documentation 
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use crate::operator::traits::{MutationOperator, Operator};
use crate::solution::Solution;
use crate::utils::random::Random;

/// Swap mutation for permutation solutions.
///
/// Preserves permutation validity by swapping indexes.
#[derive(Clone)]
pub struct SwapMutation {
    name: String,
}

impl SwapMutation {
    pub fn new() -> Self {
        Self {
            name: "SwapMutation".to_string(),
        }
    }
}

impl Default for SwapMutation {
    fn default() -> Self {
        Self::new()
    }
}

impl Operator for SwapMutation {
    fn name(&self) -> &str {
        &self.name
    }
}

impl MutationOperator<usize> for SwapMutation {
    fn execute(&self, solution: &mut Solution<usize>, probability: f64, rng: &mut Random) {
        let n = solution.num_variables();
        if n < 2 {
            return;
        }

        let p = probability.clamp(0.0, 1.0);
        if rng.next_f64() >= p {
            return;
        }

        let i = rng.range(n as u64) as usize;
        let mut j = rng.range(n as u64) as usize;
        if j == i {
            j = (j + 1) % n;
        }

        let _ = solution.swap_variables(i, j);
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn name_is_exposed() {
        let mutation = SwapMutation::new();
        assert_eq!(mutation.name(), "SwapMutation");
    }

    #[test]
    fn keeps_same_length() {
        let mutation = SwapMutation::new();
        let mut solution = Solution::new(vec![0, 1, 2, 3, 4]);
        let mut rng = Random::new(42);

        mutation.execute(&mut solution, 1.0, &mut rng);
        assert_eq!(solution.num_variables(), 5);
    }

    #[test]
    fn zero_probability_leaves_solution_unchanged() {
        let mutation = SwapMutation::new();
        let mut solution = Solution::new(vec![0, 1, 2, 3, 4]);
        let original = solution.variables().to_vec();
        let mut rng = Random::new(42);

        mutation.execute(&mut solution, 0.0, &mut rng);

        assert_eq!(solution.variables(), original.as_slice());
    }

    #[test]
    fn one_mutation_preserves_permutation_membership() {
        let mutation = SwapMutation::new();
        let mut solution = Solution::new(vec![0, 1, 2, 3, 4]);
        let mut rng = Random::new(42);

        mutation.execute(&mut solution, 1.0, &mut rng);

        let mut genes = solution.variables().to_vec();
        genes.sort_unstable();
        assert_eq!(genes, vec![0, 1, 2, 3, 4]);
    }
}