Yes, that works as expected.
BUT consider:
__ q: 360 NB. generate a table of primes and powers:
2 3 5
3 2 1
((3+3*>:i._10),:~p:i.10) NB. set up a bigger table
2 3 5 7 11 13 17 19 23 29
33 30 27 24 21 18 15 12 9 6
NB. generate a number from it:
__ q: N NB. __ q: factors it quite fast
2 3 5 7 11 13 17 19 23 29
33 30 27 24 21 18 15 12 9 6
_ q: N NB. so does _ q:
33 30 27 24 21 18 15 12 9 6
ts'__ q: N'
0.0001254 45504
ts'_ q: N'
0.0001236 61696
*/>:_ q: N NB. the number of divisors is quite large!
4490309824000
*/>: 33 30 27 24 21 18 15 12 9 6 NB. checking result
4490309824000
The performance of q: in its various guises will of course deteriorate
with the
presence of large prime factors!
Anyway, it's advisable not to generate all divisors here unless you
really need them!
Cheers,
Mike
Note - I've trimmed the history below here...
On 25/04/2020 03:47, Devon McCormick wrote:
I found this one in my bag of tricks:
allFactors=: */&>@{@((^ i.@>:)&.>/)@q:~&__
#,allFactors */p:i.10
1024
On Fri, Apr 24, 2020 at 7:15 PM 'Mike Day' via Programming <
[email protected]> wrote:
Numbers of divisors below, not the divisors themselves... the thread had
split! I was attempting to comment on Hauke Rehr’s post.
M
Sent from my iPad
On 24 Apr 2020, at 23:52, 'Jon' via Programming <
[email protected]> wrote:
This is missing a few divisors. It seems Skip's original method would be
difficult to beat. It's O(n) in time and space. You could improve space
complexity by doing a simple loop, but as far as I can see there are no
shortcuts, and the best way is to just "brute force" it.
Sent from BlueMail
On Apr 25, 2020, 5:35 AM, at 5:35 AM, 'Mike Day' via Programming <
[email protected]> wrote:
I think this is near to the approved way:
(*/"1@:>:@(_& q:))24 360 4711
8 24 4
Mike
Sent from my iPad
On 24 Apr 2020, at 21:13, Hauke Rehr <[email protected]> wrote:
I now have an answer for the number of results:
*/ >: +/"1 (=/~ ~.) q: 4711
4
*/ >: +/"1 (=/~ ~.) q: 42
8
I hesitate using =/~ (it’s actually deprecated)
but I wouldn’t know a better way in this case
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