__ q: I meant..
Thanks,
—
Raul
On Monday, March 11, 2019, Raul Miller <rauldmil...@gmail.com> wrote:
> That’s a good approach.
>
> The _ q: representation is really nice for this task.
>
> Thanks,
>
> —
> Raul
>
> On Monday, March 11, 2019, Eugene Nonko <eno...@gmail.com> wrote:
>
>> Here's the solution I ended up using:
>>
>> _&q:^:_1 >./ _ q: >: i. 10000x
>>
>> Just factorize to prime exponents representation, find maximums and
>> convert
>> back from prime exponent representation.
>>
>> On Sun, Mar 10, 2019 at 2:35 PM Raul Miller <rauldmil...@gmail.com>
>> wrote:
>>
>> > J's extended precision integer implementation is part of it. But
>> > floating point numbers don't really work for this kind of problem for
>> > anything longer than i.11
>> >
>> > But, also, I imagine a part of this also might be that Haskell has
>> > optimizations which improve performance of this kind of problem, which
>> > we don't have in J.
>> >
>> > Here's a J approach that gets the solution to this kind of problem a bit
>> > faster:
>> >
>> > lcmseq=:3 :0
>> > primes=. i.&.(p:inv) y
>> > maxsq=. 1+primes I.%:y
>> > */primes^x:1>.(#primes){.<.(maxsq{.primes)^.y
>> > )
>> >
>> > lcmseq 100000x
>> >
>> > 695283836241707197000307586526418388339874291768035113536027
>> 537561504144217502123750625798682860204776361287769787645489
>> 273366008105870757535968316298519927347209547516689789186138
>> 157883056062709938348338270956051626062862418050487468112737
>> 2319705939469099...
>> > 6!:2'lcmseq 100000x'
>> > 0.398073
>> >
>> > I hope this helps,
>> >
>> > --
>> > Raul
>> >
>> > --
>> > Raul
>> >
>> > On Sun, Mar 10, 2019 at 5:10 PM james faure <james.fa...@epitech.eu>
>> > wrote:
>> > >
>> > > That, I suspect, can be blamed mostly on the abysmally slow extended
>> > precision integers in J, and the fact that *. must manipulate these
>> > extended precision integers more often than other verbs.
>> > >
>> > > Indeed, If you remove the 'x', it runs extremely fast.
>> > > ________________________________
>> > > From: Programming <programming-boun...@forums.jsoftware.com> on
>> behalf
>> > of Eugene Nonko <eno...@gmail.com>
>> > > Sent: Sunday, March 10, 2019 9:00 PM
>> > > To: programm...@jsoftware.com
>> > > Subject: [Jprogramming] LCM performance
>> > >
>> > > I need to find the smallest number that divides all numbers from 1 to
>> n.
>> > > The solution, of course is this:
>> > >
>> > > *./ >: i. n
>> > >
>> > > What I don't understand is why this solution seems to scale so poorly:
>> > >
>> > > 6!:2 '*./ >: i.10000x'
>> > > 0.326128
>> > > 6!:2 '*./ >: i.11000x'
>> > > 1.00384
>> > > 6!:2 '*./ >: i.12000x'
>> > > 4.133
>> > > 6!:2 '*./ >: i.13000x'
>> > > 11.8082
>> > >
>> > > When I perform similar calculation in Haskell it produces result in
>> > > negligible time, even when n = 100,000.
>> > >
>> > > λ: foldr1 lcm [1 .. 100000]
>> > > 695283836241707197000307586...
>> > >
>> > > If I use a verb other than *. it runs very quickly, as expected.
>> > >
>> > > What's so special about LCM?
>> > >
>> > > Thanks,
>> > > Eugene
>> > > ------------------------------------------------------------
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>> s.htm
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