I happened to stumble across some GMP benchmarks for calculating pi(x). May
interest you
https://gmplib.org/pi-with-gmp.html
--------------------------------------------
On Thu, 3/24/16, Mike Day wrote:
Subject: Re: [Jchat] primes
To: [email protected]
Date: Thursday, March 24, 2016, 12:36 AM
Sorry not to be clear.
I'd come across a Python
function to calculate primepi and/or sum of
primes.
I translated it into c,
J and Pari GP with the sorts of performance
times indicated.
The method
rests on these properties:
N(v,p) =
N(v,p-1) - (N(v/p, p-1) - N(p-1,p-1))
S(v,p) = S(v,p-1) - p(S(v/p, p-1) - S(p-1,p-1))
where N(v,m) (S(v,m)) is the number (sum) of
integers in [2,v] that
remain after
sieving by all primes smaller than or equal to
m .
The implementation is clever in that it
doesn't need to explicitly
include all
integers
in the sieve, but instead uses a
couple of arrays of size ~ root(n).
My Lehmer effort is based on Weisstein's
description in Wolfram World,
and is
MUCH more complicated and less J-like than what
I chose to call primepi.
FYI, I've just rediscovered my note to
self on the apparent error in
Weisstein's
description:
" NB. Line 1 is wrong; the limits on i,j
should read 1<=i (ie
_not_ 1<=i<=j<=a )
OK?
Mike
PS - sorry that table of (very approx) timings
displayed poorly for you.
On 23/03/2016 13:33, 'Jon
Hough' via Chat wrote:
> Sorry,
I'm confused, what's the difference between primepi
and lehmer?
>
>
Anyway, it seems your J Lehmer implementation calculates
pi(1e9) in ~2 seconds.
> That doesn't
seem bad. I mean it's usable.
>
--------------------------------------------
> On Tue, 3/22/16, Mike Day
wrote:
>
> Subject: Re: [Jchat]
primes
> To: [email protected]
> Date: Tuesday, March 22,
2016, 7:32 PM
>
> fwiw, I messed around
> with primepi(n) and
sum-of-primes-to(n) a few months
> ago. (Sum of primes can be
dealt with in a
> similar
fashion to
> primepi).
Lehmer
> didn't perform
well in my attempts to apply
> it. The Wolfram
page on
> Lehmer
> used to have an error in
> one of the summations, so
take care if using
> http://mathworld.wolfram.com/LehmersFormula.html
> (I'm sorry but I
can't see if it's
> still wrong right now.
Weisstein didn't
> acknowledge an attempt to
report the problem,
> and I
naven't retained a
> copy of
> my message.)
>
> Timings for primepi(n), on
a previous
> laptop:
>
+------+----------+-------+-------+--------+-----+-----+-----+----+------+
> |Times |n=
|1000000|1e7 |1e8
> |1e9
|1e10 |1e11 |1e12|1e13 |
>
+------+----------+-------+-------+--------+-----+-----+-----+----+------+
> |c++~
|primepi |1ms |5ms
>
|14ms |150ms|1.1s |9.4s |86s |13m05s|
>
+------+----------+-------+-------+--------+-----+-----+-----+----+------+
> |J
|primepi |1ms
> |6ms |20ms |62ms
|3.4s |16.6s|92s |8m15s |
>
+------+----------+-------+-------+--------+-----+-----+-----+----+------+
> |J |Lehmer
|4ms
> |22ms |190ms |2.2s
|8m23s|....
> |....|....
|
>
+------+----------+-------+-------+--------+-----+-----+-----+----+------+
> |PariGP|my-primepi|100ms
|616ms |4.4s
> |34.6s|4m27s|....
|....|.... |
>
+------+----------+-------+-------+--------+-----+-----+-----+----+------+
> |PariGP|built-in
> |0.004ms|0.327ms|0.0011ms|104ms|27.8s|....
|....|.... |
>
+------+----------+-------+-------+--------+-----+-----+-----+----+------+
>
> (Apologies if this
doesn't
> display well -
I've tried!)
>
> On the present laptop, with
an amd chip:
> _1 p:
<.1e8
>
> 5761455
>
>
> timer'{.{:primepi
<.1e8'
>
> +---------+-------+
>
> |0.0179977|5761455|
>
> +---------+-------+
>
>
_1 p:
> <.1e10
>
> |limit error
>
> | _1 p:<.10000000000
>
>
> timer'{.{:primepi
<.1e10'
>
> +-----+---------+
>
> |3.857|455052511|
>
> +-----+---------+
>
>
> As the
> comparisons above
demonstrate, my attempt at coding Lehmer
> in J
> performed
poorly. I code c
> and c++ very naively, not
knowing them well,
> so
it's not surprising that J outperforms
> my c++ effort for larger
n.
> The first row of
> the Pari GP times are for my
attempt at translating my
> J function into its script.
Pari GP's
> built-in
primpi function has is
> very fast
> for lower n, but degrades
sharply for larger values. It
> might be
> relevant that I initialise GP
with
> parisize = 8000000,
primelimit =
> 4270000000
>
> The
> downside, as others have
said, is that an efficient
> primepi
> function does
> NOT
> scan all primes on its way to
counting or summing them!
>
> Code available if
> interested.
>
> Mike
>
> On 22/03/2016 00:31,
'Jon
> Hough' via
Chat wrote:
> > Since p:
has
> a limit (why is that,
by the way? I have written a pi(x)
> function using Miessel's
formula in another language and
> it does grind to a slowdown
for values much larger than 1e7,
> so that might be the reason.
I'm assuming internally J
> uses Miessel or Lehmer's
formula.),
> >
> it might be better to
"cheat" and just use a
> hardcoded value for
pi(1e9).
> >
> > https://primes.utm.edu/howmany.html
> (scroll down to table 1)
> >
> >
> > Also, possibly the
> worst idea ever, why not
iterate from 2 to 1e9 and do prime
> tests and keep a record of
the previously found prime to
> compare the final digits with
the next prime, and keep a
> record of the comparisons.
Probably hopelessly slow, and
> inefficient.
> >
> >
> --------------------------------------------
> > On Tue, 3/22/16, Raul
Miller
> wrote:
> >
> > Subject:
Re: [Jchat]
> primes
> > To:
"Chat
> forum"
> > Date:
Tuesday, March 22,
> 2016,
12:14 AM
> >
> > Oh, I coded
wrong. The
> > limit error
was from p:, but
> I should
not have been
> > feeding it
the value 1e9.
> >
> > Sometimes I
wonder how I get
> anything
> > done...
> >
> > Thanks,
> >
> > --
> > Raul
> >
> >
> > On Mon,
Mar
> > 21,
2016 at 11:03 AM, Roger
> Hui
> > wrote:
> >
> > >
> > > it
should be
> straightforward
to do the extra credit
> > problem
> > >
> > > I
should
> > have
checked. The extra
> credit problem is for
100,000,000
> > primes.
> > >
> > >
_1 p:
> > _1+2^31
> > >
105097564
> > >
p: 1e8
> > >
> > 2038074751
> > >
> > > So
the
> > limit error
is not in p: .
> > >
> > >
> > >
> > >
> > >
> > >
> > > On
Sun, Mar 20, 2016
> > at 4:44 PM,
Raul Miller
>
> > >
wrote:
> > >
> > > >
Rosettacode has a
> task
now, for this
> > item.
> > >
>
> > > >
http://rosettacode.org/wiki/Prime_conspiracy#J
> > >
>
> > > >
And,
> > hypothetically
speaking, it
> should be
straightforward to do
> > the
> > >
extra
> > >
>
> > credit
problem. But that
> doesn't work. Given:
> > >
>
> > > >
dgpairs=: 2
> > (,'->',])&":/\
> 10 | p:
> > >
>
> combine=: ~.@[ ,.~
' ',.~
> > ":@,.@(+//.)
> > >
>
> > > >
We can try this:
> > >
> > >
> > > >
/:~
> combine&;/|:
> > (~.;#/.~)@dgpairs@((+
> i.)/)"1
> > >
>
> > (1e6*i.1e3),.1e6+999>i.1e3
> > >
>
> > > >
|limit error:
> dgpairs
> > >
>
> > > >
... but p:
> > doesn't
work for values
> like 1e9
(1 p: works, but not
> > p:
> > > >
itself).
> > >
> > >
> > > >
And, for example,
> Roger
has
> > worked out
some
> ways of dealing with
large
> > > >
primes -- see
> looking
at
> > >
> http://code.jsoftware.com/wiki/Essays/Primality_Tests
> > -- but we
don't
> > >
have
> > > >
anything that's
> a drop
in
> > replacement
for
> the p: monad.
> > >
>
> > > >
So this presents
> something
of a
> > problem
-
> how would we tackle a
problem
> > >
> > > like
this?
> > >
>
> > > >
(Please feel free
> to
change forum to
> > programming
if you've got
> working
> > >
> > code
> > > >
rather than just
> > ideas...).
> > >
>
> > >
> > >
Thanks,
> > >
>
> > >
> > > --
> > > >
Raul
> > >
> > >
> > >
>
> > >
>
> > >
>
> > > >
On Tue, Mar
> > 15, 2016 at
7:02 AM, Cliff
> Reiter
> > > >
wrote:
> > >
>
> > > >
> A look at the
> frequencies of
> > pairs of
> last digits of successive
primes:
> > > >
>
> > /:~({.,#)/.~2]\10|p:4+i.1e7
> > >
>
> > >
> > > >
> 1 1 446808
> > > >
>
> > > >
> 1
> > 3
756071
> > > >
>
> > >
> > > > 1
7 769924
> > > >
>
> > > >
> 1 9 526953
> > >
> > >
>
> > > >
> 3 1 593196
> > > >
>
> > > >
> 3
> > 3
422302
> > > >
>
> > >
> > > > 3
7 714795
> > > >
>
> > > >
> 3 9 769915
> > >
> > >
>
> > > >
> 7 1 639383
> > > >
>
> > > >
> 7
> > 3
681759
> > > >
>
> > >
> > > > 7
7 422289
> > > >
>
> > > >
> 7 9 756852
> > >
> > >
>
> > > >
> 9 1 820369
> > > >
>
> > > >
> 9
> > 3
640076
> > > >
>
> > >
> > > > 9
7 593275
> > > >
>
> > > >
> 9 9 446032
> > >
> > >
>
> > > >
> The 1 follows
> 1 as
> > rare as 9
follows 9,
> but rarer is 3
follows 3 as
> > >
rare
> > > >
> as 7
> > follows 7.
9 1 most popular!
> Very
curious. Probably should
> > move to
> > > >
> JProg'
> Best,
> > Cliff
> > > >
>
> > >
> > >
>
> > > >
>
> > > >
>
> > > >
>
> > On
3/14/2016 12:03 PM, R.E.
> Boss wrote:
> > >
> > >
>
> > > >
>>
> > > >
>>
> > >
>
> > >
https://www.quantamagazine.org/20160313-mathematicians-discover-prime-conspiracy/
> > > >
>> R.E.
> Boss
> > > >
>>
> >
----------------------------------------------------------------------
> > > >
For
> > >
>
> > >>
information about J
> forums
see http://www.jsoftware.com/forums.htm
> > >
> > >
>>
> > > >
>
> > > >
>
> >
----------------------------------------------------------------------
> > > >
> For
> information about
J forums
> > see http://www.jsoftware.com/forums.htm
> > > >
>
> > >
>
> >
----------------------------------------------------------------------
> > > >
For information
> about J
forums see http://www.jsoftware.com/forums.htm
> > >
>
> > >
> >
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> > > For
information about J
> forums
see http://www.jsoftware.com/forums.htm
> > >
> >
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> forums
see http://www.jsoftware.com/forums.htm
> >
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>
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