Function for_each_chunk_init 

pub fn for_each_chunk_init<S, I, F>(
    output: &mut [f32],
    chunk_len: usize,
    work_per_chunk: usize,
    init: I,
    f: F,
)
where
    I: Fn() -> S + Send + Sync,
    S: Send,
    F: Fn(&mut S, usize, &mut [f32]) + Send + Sync,

Chunk-parallel sibling of for_each_row; chunks are never split.