Function horizontal_visibility_parallel 

pub fn horizontal_visibility_parallel<T>(
    series: &TimeSeries<T>,
) -> Vec<(usize, usize, f64)>
where
    T: Copy + PartialOrd + Into<f64> + Send + Sync,

Computes horizontal visibility edges in parallel (requires parallel feature).

Uses O(n) envelope optimization within each parallel chunk for better efficiency than the naive O(n²) parallel approach.

Performance

Best for large graphs (>1000 nodes) on multi-core systems. Expected speedup: 2-4x on 4-8 cores.