At 07:08 AM 6/28/99 +0100, you wrote:
> > I *suspect* that in light of GIMPS' success, he is likely looking much
> > higher than we are now (and has been for some time, again as a
> guess). He
> > knows our current program cannot top P > 20,000,000, so I suspect he's
> > above that range, perhaps by a good margin. It may be that he breaks
> GIMPS
> > record(s) again someday.
>
>Are you sure about this?
By no stretch of anyone's imagination. As I said, i don't know David from
Adam, and have never talked to him, even by Email. My speculation was a
SWAG, and could be 180 degrees from the truth. Your own information about
his ability to get CPU time does tend to contradict my guesses, which were
based on the heresay I noted below.
>George told me that he'd asked David S. to
>verify the newly-discovered prime, but that David was having
>difficulty getting access to sufficient CPU time & would only be able
>to run in the background, taking approx. 4 weeks. Several others of
>us would be able to do an independent double-check run on a 6 million
>range exponent in that time, e.g. I could use MacLucasUNIX on my 533
>MHz Alpha 21164 & complete in 4 weeks (ish). Which is why I contacted
>George, to offer my services.
>
> > I do know that the last time George expanded
> > Prime95 to hunt up to 20MM (up from 3MM), that George sent several
> residues
> > in the upper ranges to David for confirmation, and that David was able to
> > confirm SOME of them rather quickly (faster than a Cray could do the
> > calculations on the spot, so they were already tested). This to me
> > indicates that David is searching the numbers far above our top potential
> > range, especially since a Cray can test such numbers in about a week or
> > two, as a guess.
>
>Well - for testing the algorithm you don't neccessarily have to run
>to completion - I've also run quite a number of exponents between 10
>and 20 million to 400 iterations for the purpose of cross-checking
>results. And I'll be doing a lot more when I get sufficient memory.
While not CERTAIN, I'm fairly sure that the test values David confirmed
were of "last iteration" residues.
>Verification of 3021377 took DS 8 hours on "his" Cray. A "square law"
>seems reasonable (run time = #iterations * time per iteration, time
>per iteration is O(n log n) where n is the FFT size) so, 20 million
>being approx. sqrt(50) times 3 million, run times of 50 * 8 hours =
>2.5 weeks would be expected - assuming unlimited access to the whole
>system. For exponents >33.22 million (10 million digit numbers) he'd
>be well into months per test.
YOWCH! How long on a P-III/450, or an Athlon (K7), then?
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