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Old 2003-11-27, 07:12   #1
Xyzzy's Avatar
Aug 2002

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Default P-1 Memory...

Some weird numbers... Any thoughts? (These are for a ~4M exponent!)
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Old 2003-11-27, 19:33   #2
garo's Avatar
Aug 2002
Termonfeckin, IE

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Umm... what's weird about this?
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Old 2003-11-27, 20:33   #3
Xyzzy's Avatar
Aug 2002

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The slight increase in the chance you have of finding a factor doesn't look like it is worth the trouble of assigning extra memory... Of course I knew that giving it more memory would not make it any faster, but up until now I never would have considered using such a low amount of memory on a P-1 test...

In other words, work here in Marin's Mersenne-aries needn't be limited to people who have gobs of memory...
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Old 2003-11-27, 22:26   #4
GP2's Avatar
Sep 2003

50348 Posts

But that's for a small (~4M) exponent.

What do you get for, say, 11M exponents?
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Old 2003-11-27, 23:04   #5
garo's Avatar
Aug 2002
Termonfeckin, IE

53138 Posts

Well, if you look at the bounds calculation code, you will find that Prime95 is interested in maximizing the throughput of the project and not necessarily the individual machine. The bounds are calculated such that

(Time for 2 LL tests * chance of finding factor) - Time for P-1 test

is maximized

Note that GIMPS actually uses a multiple other than2 but I don't remember it exactly.

So, in effect it may be more beneficial for the project but your machine may end up finding factors at a slower rate.
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Old 2003-11-27, 23:38   #6
nfortino's Avatar
Nov 2003

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This is the expected data trend from the command line:

As garo has said, the program optimizes the bounds so that the processing time is most beneficial to the project. When you allocate more memory, it allows the second stage to run with larger bounds, but also allows the smaller bounds to run faster. This inturn allows deeper bounds with the same amount of time, explaining the slight increase in the B2 bound. However, since you goal is to find a factor, you should use a different command line.

From readme.txt: “The P-1 choice lets you factor Mersenne numbers using the P-1 method of factoring. There is presently no web site which tells you how much P-1 factoring has already been done on exponents. You can also edit the worktodo.ini file directly. For example:
The first value is the exponent. The second value is bound #1. The third value is bound #2. The fourth value is 0 for 2^N-1 factoring, 1 for 2^N+1 factoring. The fifth value is no longer used.”

For some reason, this is not mentioned in undoc. I have no idea how to calculate the proper bounds from a set memory allocation.

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Old 2004-01-06, 22:02   #7
crash893's Avatar
Sep 2002

23·37 Posts

the time seems to be pretty stable

but by my ( very questiobable) perdictions

you would need something like 200 gigs of ram to get near 100% chance of finding a factor every time.
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Old 2004-03-12, 13:34   #8
koekie's Avatar
Dec 2002
Amsterdam, Netherlands

1148 Posts

Originally Posted by crash893
you would need something like 200 gigs of ram to get near 100% chance of finding a factor every time.
Maybe we can ask the US goverment if we can borrow some of this ram
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