On 1/11/20 6:57 PM, John Cowan wrote:
> (array-inner-product sum product a1 a2) => constructs the inner product
> (dot product, matrix product) of a1 and a2, using the dyadic function
> *product* to multiply individual elements and the variadic function
> *sum* to total them.  It is an error if the bounds of the last dimension
> of a1 are not equal to the bounds of the first dimension of a2; the
> bounds of the result are all the remaining bounds of a1 followed by all
> the remaining bounds of a2.

Is sum a "reduction" (which needs no identity element) or a "fold"
(which does)?  Which APL operator is this?

Brad