On 28 Jun 99, at 21:59, Gordon Spence wrote:
> "Finally, if a factor is later found for a Mersenne number or the
> Lucas-Lehmer result is found to be incorrect, then you will "lose credit"
> for the time spent running the test."
I obviously can't answer for George. PrimeNet works a different way,
Scott credits any work submitted in good faith, whatever happens
thereafter. I think George's idea was to encourage people to do the
appropriate amount of trial factoring - if you didn't do enough, and
proceed to run the LL test, you lose the credit because you should
have done more factoring to start off with. Otherwise you maximize
your credit by simply running LL tests & ignoring factoring
altogether.
The problem with this approach is that goalposts shift. Different
processor types have different LL test:factoring performance ratios,
in particular the "plain Pentium" (Intel Pentium "classic" and Socket
7 MMX processors) are rather poor at factoring compared with most
other processor types, and processors with high core:bus speed ratios
are going to be (relatively) better at factoring because of the lower
memory bus load. Consequently the appropriate factoring depth varies
to some extent depending on the mix of processors in use.
>
> It is on <www.mersenne.org/top.htm> always struck me as odd I must admit.
> At the time the test was done it obviously WAS required, so why the
> subsequent penalty when we make advances and can factor much deeper?
>
I agree. However, to take the point to a ridiculous extreme, finding
a factor saves running a LL test - so why can't I have credit for
finding 54,522 (small) factors in the range 33.2 million to 36
million, thus saving (very approximately) 54,522 * 8 P90 CPU years LL
testing? The job ran in an hour on a PII-350!
Somewhere in here there is a compromise. I'd suggest:
(a) you should lose _double_ credit for a LL test if the result is
proved incorrect, or if a factor is found in a range which you claim
to have checked;
(b) a table should be published of the suggested factoring depths for
various exponent ranges. If you submit a LL test result, then someone
finds a factor less than the table depth at the date you submitted
the result, you lose the credit; otherwise, you keep the credit;
(c) however deep you factor, you only get credit for factoring to the
table depth in the current table.
BTW I don't really understand why PrimeNet doesn't credit you for
results obtained when the manual testing pages are used instead of
the automatic system. I suppose Scott is trying to promote the
automatic system, and I'm in agreement with that sentiment, but it
still seems a bit strange to me.
Regards
Brian Beesley
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