More procedures:

make-diagonal-array is like make-identity-array, except that it takes
a vector of numbers and uses them to populate the principal diagonal
rather than populating it with ones.

Predicates:  identity-array?, diagonal-array?,
upper-triangular-array?, lower-triangular-array?, symmetric-array?.

On Sat, Apr 11, 2026 at 11:41 PM John Cowan <xxxxxx@ccil.org> wrote:
>
> Numerical arrays:
>
> Except insofar as the storage class constrains the elements of an
> array, the operations of SRFI 231 do not care what type the values
> have, so operations that depend on numerical elements aren't
> available. Here are a few ideas for suitable procedures:
>
> Matrix addition, subtraction, and {Hadamard, cross, dot} products are
> trivial to do with array-map, array-inner-product and
> array-outer-product, but we could have wrappers for them with more
> obvious names: as in Racket, these could be macros.
>
> (make-identity-array storage-class dimensions size) returns an
> n-dimensional hypercube of real numbers where every dimension has a
> lower bound of 0 and an upper bound of size, and every element on the
> principal diagonal is 1 and every other element is zero.  I suppose
> this would normally be used with a non-generic storage-class, but
> there might be some way to specify if the values are exact or inexact
> for use with generic-storage-class.(array-determinant array) returns
> the determinant of a matrix.  I don't know how this generalizes, if at
> all, to higher dimensions.
>
> (array-divide array1 array2) returns the matrix divide of array1 and
> array2. I don't know how this generalizes, if at all, to higher
> dimensions.
>
> (array-invert array1) is the result of dividing an appropriately sized
> identity array by array1.  Again, I don't know if this generalizes.
>
> How about FFTs?  Racket supports FFT over a specified dimension or all
> dimensions, plus their inverses.