chickadee » srfi-179 » array-sample

We assume that array is an array all of whose lower bounds are zero, and scales is a vector of positive exact integers whose length is the same as the dimension of array.

Informally, if we construct a new matrix $S$ with the entries of scales on the main diagonal, then the $\vec i$th element of (array-sample array scales) is the $S\vec i$th element of array.

More formally, if array is specialized, then array-sample returns

(specialized-array-share
 array
 (interval-scale (array-domain array)
                 scales)
 (lambda multi-index
   (apply values
          (map * multi-index (vector->list scales)))))

with the result inheriting the safety and mutability of array.

Otherwise, if array is mutable, then array-sample returns

(make-array
 (interval-scale (array-domain array)
                 scales)
 (lambda multi-index
   (apply (array-getter array)
          (map * multi-index (vector->list scales))))
 (lambda (v . multi-index)
   (apply (array-setter array)
          v
          (map * multi-index (vector->list scales)))))

Finally, if array is immutable, then array-sample returns

(make-array
 (interval-scale (array-domain array)
                 scales)
 (lambda multi-index
   (apply (array-getter array)
          (map * multi-index (vector->list scales)))))

It is an error if array and scales don't satisfy these requirements.