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-   -   Does NewPGen have a bug? (https://www.mersenneforum.org/showthread.php?t=23735)

 chunsonnn 2018-10-26 04:11

Does NewPGen have a bug?

I was sieving k=173 from n=1M to n=2M, and I found this message by NewPGen:

p=2215115304221 divides n=1798220.

However 2,215,115,304,221 is composite (that number is 8627 * 256765423), so that message should not have popped up. Why didn't NewPGen remove n=1798220 when it was at p=8627 or at p=256765423?

In case anyone's wondering, I was using NewPGen version 2.82 on a Pentium 4 computer. The problem also appears on another Pentium 4 machine, so I'm pretty sure it's not a hardware problem.

Thank
Cristiano

 axn 2018-10-26 04:31

[QUOTE=chunsonnn;498765]I was sieving k=173 from n=1M to n=2M, and I found this message by NewPGen:

p=2215115304221 divides n=1798220.

However 2,215,115,304,221 is composite (that number is 8627 * 256765423), so that message should not have popped up. Why didn't NewPGen remove n=1798220 when it was at p=8627 or at p=256765423?

In case anyone's wondering, I was using NewPGen version 2.82 on a Pentium 4 computer. The problem also appears on another Pentium 4 machine, so I'm pretty sure it's not a hardware problem.

Thank
Cristiano[/QUOTE]

p=22151153042[B]1[/B]1 divides 173*2^1798220-1

 paulunderwood 2018-10-26 06:28

Isn't k=173 already sieved very deeply by PrimeGrid?

 ATH 2018-10-26 12:01

Neither 8627 nor 256765423 is a factor of 173*2^1798220-1, so it must have been p=2215115304211 as axn pointed out.

 pinhodecarlos 2018-10-26 12:08

[QUOTE=paulunderwood;498768]Isn't k=173 already sieved very deeply by PrimeGrid?[/QUOTE]

Yes and tested up to n=2.04M by RPS.

 rogue 2018-10-26 13:26

Why are you using newpgen for this form? Use srsieve/sr1sieve. They are much, much faster than newpgen for this form.

 storm5510 2020-03-11 12:13

[U]Does [I]NewPGen[/I] have a bug[/U]? Possibly. I noticed for any given range of [I]n's[/I], [I]NewPGen[/I] will remove more [I]n's[/I], and at lower values of [I]p[/I], than the[I] srXsieve[/I] family.

Either [I]NewPGen[/I] is removing [I]n's[/I] it should not or [I]srXsieve[/I] family is not removing [I]n's[/I] it should. A combination of both is also possible. I have no way to determine which case it may be.

 VBCurtis 2020-03-11 16:54

[QUOTE=storm5510;539384][U]Does [I]NewPGen[/I] have a bug[/U]? Possibly. I noticed for any given range of [I]n's[/I], [I]NewPGen[/I] will remove more [I]n's[/I], and at lower values of [I]p[/I], than the[I] srXsieve[/I] family.

Either [I]NewPGen[/I] is removing [I]n's[/I] it should not or [I]srXsieve[/I] family is not removing [I]n's[/I] it should. A combination of both is also possible. I have no way to determine which case it may be.[/QUOTE]

Please elaborate, with example files. The OP's post is surely a typo, while yours is a serious allegation.

 storm5510 2020-03-15 13:46

[QUOTE=VBCurtis;539426]Please elaborate, [U]with example files[/U]. The OP's post is surely a typo, while yours is a serious allegation.[/QUOTE]

"Serious allegation." I do not consider it as being such. I am not condemning either. Just a simple comparison.

I can provide example files. It may take a couple of days. I am running a wide-range sieve on my HP to 1.5-trillion. I can replicate this with [I]NewPGen[/I] on my laptop. My i7 is running a double-instance of [I]LLR[/I] so I cannot use it.

[U]Edit[/U]: I will allow the [I]srXsieve[/I] on the HP to finish, and then run the [I]NewPGen[/I] test after it. [I]sr1sieve[/I] estimates completion on March 17 at around 19:00 UTC.

 pepi37 2020-03-15 17:18

[QUOTE=storm5510;539767]"Serious allegation." I do not consider it as being such. I am not condemning either. Just a simple comparison.

I can provide example files. It may take a couple of days. I am running a wide-range sieve on my HP to 1.5-trillion. I can replicate this with [I]NewPGen[/I] on my laptop. My i7 is running a double-instance of [I]LLR[/I] so I cannot use it.

[U]Edit[/U]: I will allow the [I]srXsieve[/I] on the HP to finish, and then run the [I]NewPGen[/I] test after it. [I]sr1sieve[/I] estimates completion on March 17 at around 19:00 UTC.[/QUOTE]

Why is needed to wait so many days: take sequence you know produce "problems" runn it on NewPgen few minutes, and run it under srxsieve few minutes ( to reach same depth)
So all work can be done in 10 minutes.
Or tell us what sequence have problem and I would like to comparison for you,
For that you can only need seconds to write reply on my post

 storm5510 2020-03-17 01:51

2 Attachment(s)
I scaled this test down dramatically. The parameters are:

Series: 7*2^n-1
n: 350,000
N: 650,000
p: (default)
P: 50e9

It took [I]srsieve/sr1sieve[/I] about 30 minutes to run this. [I]NewPGen[/I], over four hours. [I]NewPGen[/I] [U]does[/U] [U]not[/U] start storing factors until it [I]p[/I] passes 2^32. So, I set the ceiling for [I]srsieve[/I] to this value. The staring [I]p[/I] for [I]sr1sieve[/I] was the same.

During the sieve [I]NewPGen[/I] pulled out 5,603 factors, [I]sr1sieve[/I] pulled out 840.
Yet, the compete files for[I] LLR [/I]were exactly the same. 7,092 elements each. Some may be familiar with [I]fc[/I], short for file compare. I compared both [I]LLR[/I] files. The [U]only[/U] difference was in the header line at the very top.

All the files are stored in the attached zip file. There is also an image attachment with [I]NewPGen[/I] set into a [I]PowerShell[/I] window where I ran [I]srsieve[/I] and [I]sr1sieve[/I].

Q: How is it possible for [I]NewPGen[/I] to flag so many more factors than [I]sr1sieve[/I] and both results files be virtually identical?

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