On 8/28/24 2:10 PM, Bradley Lucier wrote:
> I now understand that array broadcasting (or at least array-lift as
> described below) can be framed as a "Bawden-style" array transformation.

This statement is incorrect in an interesting way---array-lift as
defined in the previous email employs an affine mapping of the
multi-index argument, but that mapping is not one-to-one on the new
domain to the old domain, it is necessarily many-to-one.

The SRFI document states that the multi-index mapping argument to
specialized-array-share must be one-to-one.

The motivation is that you don't want a value stored in one location to
change the value in a "different" location.

But this motivation doesn't hold if the result is an immutable
specialized array.

So for example one could "broadcast" a one-dimensional specialized array
to all the rows of an *immutable* two-dimensional specialized array,
while keeping the one-dimensional array as the entire backing store of
the result.  Then one could apply other array transforms (permuting,
extracting, etc.) while keeping O(1)-time accesses.

I'd have to check the details to see if this would work.  Then it may be
more efficient than the NumPy implementation.  (The NumPy documentation
explicitly suggests using loops rather than array operations if the
broadcast arrays get too big.)

Brad