[m-users.] Cartesian product of two sets of things.

[Sean Charles (emacstheviking)]

Interesting, I am using -O4 as well for the ahead of time compiling of floating point operations that are constants.

> On 11 Oct 2023, at 04:50, Julien Fischer <jfischer at opturion.com> wrote:
> 
> 
> 
> On Wed, 11 Oct 2023, Zoltan Somogyi wrote:
> 
>> 
>> On 2023-10-10 21:02 +11:00 AEDT, "Julien Fischer" <jfischer at opturion.com> wrote:
>>> A big part of the difference would be that the nondet version sorts
>>> the elements and (redundantly) attempt to remove duplicates, whereas the
>>> det version just constructs the elements in reverse order directly.
>> 
>> Another source of difference is that its lowest level operations
>> are tail recursive, while the lowest level operations in the nondet version
>> can't be tail recursive, because you can't recover a nondet stack frame
>> while the values of the variables it contains may be needed to find
>> another solution.
>> 
>> You should note that even the det version in cproduct.m is not
>> as fast as it could be, because it adds each new item to the cross product
>> using a higher order call. Converting the sets to sorted lists and iterating
>> over the lists directly could replace those higher order calls with simple
>> unifications, which would make that version even faster.
> 
> Granted, although with --intermod -O3 the compiler will do that for you
> with the det version as it is written.
> 
> Julien.
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