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Old 2021-08-31, 23:33   #3095
charybdis's Avatar
Apr 2020

2·3·83 Posts

Test-sieving done, at least for today.

I only used I=16, lpb 34/35, and given the yields I don't expect anything smaller than this to be better. Even if 35/35 does sieve faster, it will make postprocessing more of a pain. The machine I used only has 16GB RAM so I can't test A=32 which requires ~26GB, but I don't think we're at a size where that would be clearly better.

Raising ncurves0 from 25 doesn't find any more relations. It could possibly be dropped a bit, but 2LP cofactorization is a tiny contribution to the total time so the effect would be negligible. ncurves1=21 does miss a few relations, but it's just a fraction of a percent, so with the extra 3LP cofactorization time I don't think there's any need to change this from the default.

There is a clear benefit of several percent from using -adjust-strategy 2, as seems to be standard with large jobs. The price paid for this is that memory use with I=16 is 13GB rather than 10GB, but I assume this won't be a problem.

Higher lims = more yield and slower sieving, and with the added complication of the duplication rate depending on the lim choice, it's not easy to measure the effects with test-sieving. 500M/800M probably isn't optimal but it'll be close enough.

mfb0 choice is always complicated by the fact that higher mfb0 leads to a small increase in the number of relations required, and we don't have a good handle on this. This makes 68 less attractive, but in the interests of keeping yield high I stuck with 67 for the main test.

mfb1 can go quite high and still show a decent improvement in sec/rel. There doesn't seem to be any problem with going as high as 102.

I test-sieved the 500M/800M, 67/102 combination at various intervals between 200M and 2500M. Sec/rel worsened from ~0.7 to ~1.5 over this range. If the aim is 3G raw relations, the range 250M-2000M looks about right, and I estimate this will take only(!) ~105 thread-years on the machine I used. This figure seems suspiciously low even given that the threads in question are fast, but I can't find a mistake anywhere, so I have to believe it. Hopefully this doesn't mean Ryan's in for a nasty surprise with the duplication rate!

Last fiddled with by charybdis on 2021-08-31 at 23:37
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