mersenneforum.org  

Go Back   mersenneforum.org > Other Stuff > Archived Projects > Prime Cullen Prime

 
 
Thread Tools
Old 2007-03-25, 18:22   #1
AntonVrba
 
AntonVrba's Avatar
 
Jun 2005

2·72 Posts
Default

How does prime95 choose the B1 and B2 constants?
Can one read about how the todo file format is interpreted?

As an experiment I tried the P-1 factoring of Prime95
which I did not know it could do. With the data as given
Prime95 estimates a 5.6% chance of finding a factor
and takes about 205 seconds to complete -
so playing around with the to do file parameters and I
changed the the ...,33,1 to ...,23,2, Now Prime95 estimates
a 34% chance of finding a factor and after 1010 seconds
P-1 found a factor in stage #2, B1=40000, B2=700000.
1625879*2^1625879+1 has a factor: 500311388963
(this factor is not found with the ...,33,1 parameter)
but the next 5 exponents could not be factored.
end of experiment.


I have no idea what would be good B1 and B2 parameters,
Maybe somebody could advise, have i jumped the gun?
is P-1 testing done in progressive stages?

Last fiddled with by AntonVrba on 2007-03-25 at 18:27
AntonVrba is offline  
Old 2007-03-25, 21:20   #2
hhh
 
hhh's Avatar
 
Jun 2005

373 Posts
Default

P-1 is two-staged.
First stage:
If there is a factor p, it will be found if p-1 has only factors below B1.
Second stage:
If there is a factor p, it will be found if p-1 has only factors below B1, except one which can lie between B1 and B2.

How to choose B1/B2?
Prime95 calculates (in a very complicated formula) the best factor throughput by taking into account
-processor type (I guess),
-memory settings (stage 2 needs a lot of mem),
-factorworth (how many LLR tests are going to be saved by a factor, that is the final 1 in the Pfactor=... line),
-and up to where it has already been sieved (that's the 33: it has been sieved up to 2^33).
If you tell him that you sieved up to 2^50, it will tell you that P-1 isn't worth it and that you should directly LLR. If you lower the sieve value, it will raise the bounds. But that's not what one should do. Better it is to have faith in the wisdom of the MASTER, and feed the program the correct values. Tomorrow, the 33 would be a 35, for example, because we will have sieved more. But that dosn't change much.

Still questions?

Yours H.

PS. there is a way to chose the bounds manually, by a command i won't tell you, but which is far from secret. H.
hhh is offline  
Old 2007-04-01, 18:46   #3
Citrix
 
Citrix's Avatar
 
Jun 2003

2·5·157 Posts
Default

Has anyone tried P+1 or ECM?

Last fiddled with by Citrix on 2007-04-01 at 18:46
Citrix is offline  
Old 2007-04-01, 18:54   #4
hhh
 
hhh's Avatar
 
Jun 2005

17516 Posts
Default

Quote:
Originally Posted by Citrix View Post
Has anyone tried P+1 or ECM?
Nope. ECM is slower than P-1, but why not, if it's still faster than LLR...
H.
hhh is offline  
Old 2007-04-02, 18:53   #5
ET_
Banned
 
ET_'s Avatar
 
"Luigi"
Aug 2002
Team Italia

2×2,383 Posts
Default

Quote:
Originally Posted by hhh View Post
Nope. ECM is slower than P-1, but why not, if it's still faster than LLR...
H.
Maybe after the end of trial-factoring to 30/35 bits ECM could be of some use, starting from the bigger exponents.

Luigi
ET_ is offline  
Old 2007-04-04, 04:59   #6
geoff
 
geoff's Avatar
 
Mar 2003
New Zealand

115710 Posts
Default

Is it worth using higher P-1 bounds than the Prime95 default, since unlike GIMPS, in this project finding a P-1 factor can also speed up the sieve a little bit?

The last field of the PFactor= line is the number of LL tests saved by finding a factor. I think this should be at least 2, maybe 3.
geoff is offline  
 

Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
P-1 discussion kladner GPU to 72 43 2012-01-27 20:43
Discussion about dates Flatlander Twin Prime Search 12 2011-11-17 09:40
10,375- LA discussion Raman Cunningham Tables 27 2008-12-04 21:17
factexcl.txt discussion hhh Prime Sierpinski Project 5 2006-11-22 17:50
New .dat discussion VJS Prime Sierpinski Project 7 2006-07-25 14:31

All times are UTC. The time now is 11:49.

Fri Sep 18 11:49:19 UTC 2020 up 8 days, 9 hrs, 0 users, load averages: 1.38, 1.57, 1.73

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.

This forum has received and complied with 0 (zero) government requests for information.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.
A copy of the license is included in the FAQ.