Re: [boost] Proposed addition to the iterator library for iterating over all tuples.

From: Larry Evans (cppljevans_at_[hidden])
Date: 2005-07-26 09:39:19

On 07/26/2005 07:25 AM, David Abrahams wrote:
> Alex Mendes da Costa <alexmdac_at_[hidden]> writes:
> 
> 
>>The iterator that I am proposing would provide the sequence (1,10),
>>(2,10), (1,20), (2,20).
> 
> 
> Oh, you want a cross-product iterator.  Interesting idea.
> 
BTW, the J or apl term for this would be "outer-product"
(produced with '/' operator) applied to the "append" operator
(','):

   ,/

IOW:

   1 2 ,/ 10 20

produces:

   1 10
   2 10
   1 20
   2 20

With another operator, for example, '+' instead of ',',
the result would be:

   11 12 21 22

See "outer-product" on p.7 of:

   http://www.jsoftware.com/books/pdf/brief.pdf

IOW, Alex's proposal is equivalent to J's:

     S1 ,/ S2

except the J result is a matrix instead of a vector,
AFAICT.

J uses the term "inner-product"[p.20] applied to '+' and '*'
operators for "matrix-product" or "cross-product".
("cross product" doesn't occur in above pdf).

A google search for outer product result in several different
definitions :(