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Old 2004-02-23, 08:48   #1
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Question I've chosen primality test task, but info shows P-1 factoring! Why ?

I've chosen primality test task, but info shows P-1 factoring! Why ?
 
Old 2004-02-23, 11:16   #2
ET_
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"Luigi"
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Quote:
Originally Posted by Unregistered
I've chosen primality test task, but info shows P-1 factoring! Why ?
Because the program tests for factors each exponent before starting a time-consuming primality test.

If you don't want it, there is a switch to avoid P-1 test.

Luigi
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Old 2004-02-23, 13:05   #3
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Quote:
Originally Posted by ET_
Because the program tests for factors each exponent before starting a time-consuming primality test.

If you don't want it, there is a switch to avoid P-1 test.

*P: Where I can find that switch?

Luigi
 
Old 2004-02-23, 16:45   #4
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Although you can skip the P-1 factoring if you really want to, please consider letting it proceed.

The bounds for P-1 factoring are chosen to maximize GIMPS throughput. That is, on average a GIMPS participant will "clear" (prove to be composite) more exponents in a given time if the automatic P-1 step is allowed to precede the L-L test. It won't change your chances of finding a Mersenne prime. If P-1 finds a factor, then the L-L test would have found that the Mersenne number is composite but you will have saved yourself the time needed to run that L-L test and can proceed to your next number assignment sooner.

Also, if you skip P-1 factoring before doing the L-L test, then later on someone else finds a factor by doing the P-1 step you skipped, you will lose GIMPS credit (on the GIMPS Top Producers list) for your L-L test, although your PrimeNet credits (on the PrimeNet Top Producers list) will remain unchanged.

Last fiddled with by cheesehead on 2004-02-23 at 16:51
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