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Old 2002-10-15, 17:56   #1
Sep 2002

68 Posts
Default SkipTrialFactoring=1 doesn't work?

On my P4 machines, I want to skip the trial factoring before running the LL test since the LL test runs very fast. The undocumented feature "SkipTrialFactoring=1" seem to be just what the doctor ordered. However, I have that in the prime.ini files and it still does trial factoring. Am I doing something wrong?

Assuming this doesn't work, can I accomplish the same thing by changing the worktodo.ini files:


By the way, I'm using 22.10 on Linux.
cmokruhl is offline   Reply With Quote
Old 2002-10-15, 19:04   #2
dswanson's Avatar
Aug 2002

20010 Posts

The "SkipTrialFactoring=1" feature bypasses the trial factorization up to n bits. In your example, "Test=13949693,65,0", trial factorization has already been completed to 65 bits so no further factorization is needed. Thus skipping the trial factoring does nothing.

It sounds like what you're really trying to skip is the P-1 factorization. Yes, changing the 0 to a 1 as you show accomplishes this.

However, from an overall GIMPS efficiency viewpoint, it'd be better if you allowed the P-1 factorization to run. George has picked the P-1 limits such that, on average, the CPU cycles expended per factor found using P-1 is less than the CPU cycles expended per LL test completed.

In other words, if you did 100 first-time LL tests with P-1 turned on, on average you'd find about 5 factors and complete 95 LL tests. If you did the same 100 first-time LL tests with P-1 turned off, you'd find 0 factors and complete 100 LL tests. But the total time spent doing those 100 LL tests would be longer than the time spend doing 100 P-1 factorizations plus 95 LL tests. So you're less efficient without P-1.
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