Thanks again, Raul.
Well - I'd actually meant ~2^24 odd numbers, 1... _1+2^25 - trust me
to make a mistake in trying to simplify the presentation! Let's call it
a typo.
I don't think my post was a spoiler, as the problem needs quite a bit
of insight elsewhere; this array helps in getting the answer.
You're right, of course, for that expression, ~50 seconds on this laptop,
which produces one extended scalar result, but unfortunately I need the
whole vector of cumulative products, 1 3 15 105...
These time and space tests are for lower size arrays:
1 ts'281474976710656&|@*/\x:1+2*i.2^10'
1.90882 628864
1 ts'datatype 281474976710656&|@*/\x:1+2*i.2^11'
7.91167 1.25146e6
1 ts'q =: 281474976710656&|@*/\x:1+2*i.2^12'
30.8606 2.49638e6
7!:5<'q' NB. space required for ~2^12 extended elements.
589824
2 10 >.@^.589824 NB. rounded up log 2 & log 10 space.
20 6
So 2^24 elements are likely to need around 2^40, 10^12 bytes.
This laptop only has about 16GB.
So, I think the cludgy "cumoddprod" or its like remains the
answer for a few more Moore cycles!
Thanks,
Mike
On 16/05/2017 13:44, Raul Miller wrote:
Forgive me for asking, but isn't 33554431 = _1+2^25 ?
Anyway, this seems to work for me:
281474976710656&|@*/x:1+2*i.2^23
I'll leave out the answer, out of respect for project euler (though
maybe the rules allow that now?).
timespacex'281474976710656&|@*/x:1+2*i.2^23'
12.457 1.67937e9
... and needs about 13 seconds and about 2 gig ram.
That said, I suppose it would be nice if x m&|@* y worked reliably for
fixed precision integers x, m and y
Thanks,
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