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-   -   Probability of finding a factor in DC p-1 (https://www.mersenneforum.org/showthread.php?t=259)

Deamiter 2002-12-13 14:06

Probability of finding a factor in DC p-1
 
I've recently been adding some older machines running DCs for me, and I just got a factor in a p-1 test. Considering that most of these should already be factored in the initial test, was this a fluke (perhaps a machine that didn't have enough memory to run p-1 completed the first test) or should I expect all of my DCs to have an equal chance of finding a factor in p-1 testing?

eepiccolo 2002-12-13 14:59

Perhaps this is an ignorant question, but what is a DC? :?

Prime95 2002-12-13 17:24

DC = double-check

Most numbers being double-checked did not have P-1 run. P-1 factoring was added in version 20, I think. So all your double-checks should have an equal chance at finding a factor. Also, prime95 should be smart enough to skip P-1 factoring if it has already been done.

cheesehead 2002-12-25 05:48

It looks like first-run LL assignments started routinely including P-1 factoring after trial factoring at roughly exponent 10 million.

DCs are now being assigned in the 88xxxxx range. It took ten months for DC assignments to advance from 76xxxxx to 88xxxxx, so I guess that new DC assignments will usually first do a P-1 for most of the next year, unless separate P-1 assignments are implemented in Primenet earlier.

cheesehead 2002-12-25 06:06

[quote="Deamiter"](perhaps a machine that didn't have enough memory to run p-1 completed the first test)[/quote]

Let me just point out to P-1 newcomers reading this that P-1 factoring has two stages, and stage 1 does not require any more than the default memory, so P-1 stage 1 factoring can proceed on any system.

Only stage 2 requires the extra (beyond the default of 8M, that is) memory you specify in Prime95's Options/CPU.../"Daytime available memory" and "Nighttime available memory". (Also, ECM factoring requires this extra memory.)


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