Function reduce 

pub fn reduce<T: Copy, A: Clone>(
    kept: (&[usize], &[isize]),
    reduced: (&[usize], &[isize]),
    data: &[T],
    offset: isize,
    out: &mut [A],
    init: A,
    f: impl Fn(A, T, usize) -> A,
    block: impl Fn(A, &[T]) -> A,
)

Folds blocks of elements: out[i] is the fold of the reduced block at output position i, starting from init. kept and reduced are (shape, strides) pairs that split the input’s dimensions; the output is row-major over kept.

Contiguous blocks are passed whole to block; other blocks are folded element by element with f, which also receives each element’s row-major index within its block. Both must compute the same fold.

Panics

As map1.