Function parallel_shortest_paths 

pub fn parallel_shortest_paths<N, E, Ix>(
    graph: &Graph<N, E, Ix>,
    sources: &[N],
    _config: &ParallelConfig,
) -> Result<HashMap<N, HashMap<N, E>>>
where
    N: Node + Clone + Send + Sync + Debug,
    E: EdgeWeight + Clone + Send + Sync + Zero + One + Add<Output = E> + PartialOrd + Copy + Debug + Default,
    Ix: IndexType + Send + Sync,

Memory-efficient parallel shortest path computation