20190509, 17:07  #67 
Jun 2003
1001000010111_{2} Posts 

20190509, 19:39  #68  
∂^{2}ω=0
Sep 2002
República de California
2×3×1,879 Posts 
Quote:
My sense is that for academicstyle compNT research like Fermat testing you're always going to need at least 2 independent runs. The academicCS types are already gonna look askance at the fact of 2 runs done using floatingpoint rather than integer math. I will post the complete set of 10Miter interim residue files online after my runs complete so anyone who desires to do so can do a parallel DC using whatever code/algorithm they like, but personally I've no interested in (IMO) wasting time on the kind of pureinteger parallel verification we did for F24. 

20190509, 20:00  #69 
Sep 2016
7·47 Posts 
Personally, I'm part of the "independent run" camp because that limits the number of failure points that can lead to an incorrect announcement.
What's the probability that GEC fails to detect an error? How many GEC checks are there? What about implementation bugs? Is it true that a single missed error among all the checks will result in an undetected wrong result? The rule that I usually follow is: "Can an adversary cause a misleading result by injecting a single error into a flawless computation at just the right place and time?" I don't know how GEC is implemented. But lets say your save file encounters a bit flip from when you wrote it to when you read it. Will it catch that? 
20190509, 22:04  #70 
∂^{2}ω=0
Sep 2002
República de California
26012_{8} Posts 
A bit of good news re. the missing data from my 60MFFT F30 run ... that was running on a 32core avx2 Xeon, the last time I was able to access said machine was late February (Feb 21, as I now can precisely date.) I knew that run was at iteration ~700M at that point, but my local copy of the runstatus file was months older, and only covered through iteration 531.4M. But!  and this is one of the reasons I keep my macbook classic's OS frozen at the wonderfully stable OS X 10.6.8, despite the attendant lackofsupport headache, and why I set my xterms to save en effectively unlimited command history  it turns out the Xterm from which I would do my severaltimesweekly runstatus quickchecks has data going all the way back to the above filedownload date, last October. And a check of whendidIlastneedtoreboot confirms:
MacBook:obj_sse2 ewmayer$ uptime 14:56 up 206 days, 15:51, 3 users, load averages: 0.22 0.24 0.39 So by simply scrolling down through said window's long captured history I was able to recover a nicely granular snapshot of the 'missing' run history. My regular runstatus checks consisted of 'tail 2 f30.stat && date', here the last portion of the thuslyrecovered history: Code:
[Feb 19 15:10:28] F30 Iter# = 681200000 [63.44% complete] clocks = 01:36:54.030 [ 0.0581 sec/iter] Res64: C120506BBDB97A13. AvgMaxErr = 0.212160316. MaxErr = 0.312500000. [Feb 19 16:50:10] F30 Iter# = 681300000 [63.45% complete] clocks = 01:39:38.457 [ 0.0598 sec/iter] Res64: 63EA4A0A58D2DCFA. AvgMaxErr = 0.212213476. MaxErr = 0.312500000. [Feb 21 20:10:37] F30 Iter# = 684600000 [63.76% complete] clocks = 01:35:04.862 [ 0.0570 sec/iter] Res64: D4F7D0654B95C2C3. AvgMaxErr = 0.212131626. MaxErr = 0.281250000. [Feb 21 21:48:03] F30 Iter# = 684700000 [63.77% complete] clocks = 01:37:22.205 [ 0.0584 sec/iter] Res64: 9E0B4E5DD7C1C0A5. AvgMaxErr = 0.212171292. MaxErr = 0.312500000. 
20190509, 23:12  #71  
P90 years forever!
Aug 2002
Yeehaw, FL
2^{3}×863 Posts 
Infinitessimal to a very large power.
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Taking all the above into account, I agree that doublechecks are still necessary, albeit at a lower priority than LL doublechecking. Last fiddled with by Prime95 on 20190509 at 23:15 

20190510, 02:47  #72  
Jun 2003
1001000010111_{2} Posts 
Quote:
A simple scheme where a single GEC run plus saving all the GECchecked full residues, should together constitute a verifiable proof. With these residues, you or anyone else can do an independent double check later. In fact, this could be a novel angle to an academic paper  how you managed to do a single run to positively verify a number using GEC! /IMO 

20190510, 06:30  #73 
Sep 2016
7·47 Posts 

20190516, 19:06  #74 
∂^{2}ω=0
Sep 2002
República de California
2·3·1,879 Posts 
Thanks to a generous donation of cycles on a 32core avx512 machine by a forumite who wishes to remain anonymous, the 60MFFT F30 run has been restarted from the 680Miter savefile. At that FFT length this machine gets 60ms/iter using 16 cores, but the  scaling deteriorates beyond that, using all 32 cores we get 50ms/iter. In contrast, David Stanfill's 32core avx2 Xeon which I had been using for that run was in the 8090ms range using 16 cores, but continued to scale nicely up to the full 32, getting 50 ms/iter as its fastest timing. More typically, due to other system loads (mainly the GPU), I got ~55 ms/iter on that one.
I am still trying to fiind out whassup w/David and the GIMPS KNL; to that end I sent email to several addresses (squirrelsresearch.com@domainsbyproxy.com, press@airsquirrels.com) last weekend, but have received no reply. I was hoping to arrange to have the KNL groundshipped to a GIMPS officer (maybe Aaron Blosser, who admins the Primenet server, has room) and then restart my 64M run on it. 
20200119, 21:37  #75 
∂^{2}ω=0
Sep 2002
República de California
2×3×1,879 Posts 
My anonymous cycle donor's continuation of my 2/3complete run of F30 @60M FFT length finished on
Friday, he has given me permission to thank him by name: it is Ryan Propper, who also did some yeoman's massDC work for GIMPS last year. Here the final residues, again the (mod 2^36) one of the nowtraditional SelfridgeHurwitz residue triplet is simply a decimalform recapitulation of the low 9 hexits of the GIMPSstyle Res64: Code:
[Jan 15 11:28:26] F30 Iter# = 1069900000 [99.64% complete] clocks = 01:34:00.016 [ 0.0564 sec/iter] Res64: D4E1ADB4D56B90F5. AvgMaxErr = 0.184720270. MaxErr = 0.281250000. [Jan 15 13:02:36] F30 Iter# = 1070000000 [99.65% complete] clocks = 01:34:05.574 [ 0.0565 sec/iter] Res64: E0A3C552712AD603. AvgMaxErr = 0.184693172. MaxErr = 0.281250000. [Jan 15 14:36:48] F30 Iter# = 1070100000 [99.66% complete] clocks = 01:34:05.895 [ 0.0565 sec/iter] Res64: 44DE22333F576C20. AvgMaxErr = 0.184676185. MaxErr = 0.281250000. [Jan 15 16:09:26] F30 Iter# = 1070200000 [99.67% complete] clocks = 01:32:33.138 [ 0.0555 sec/iter] Res64: C92DEFA95553316A. AvgMaxErr = 0.184739228. MaxErr = 0.265625000. ... [Jan 17 23:54:10] F30 Iter# = 1073741823 [100.00% complete] clocks = 00:38:54.202 [ 0.0558 sec/iter] Res64: A70C2A3DB98D6D9D. AvgMaxErr = 0.184703967. MaxErr = 0.250000000. F30 is not prime. Res64: A70C2A3DB98D6D9D. Program: E17.1 F30 mod 2^36 = 58947628445 F30 mod 2^35  1 = 26425548225 F30 mod 2^36  1 = 59810773698 These still await confirmation by way of completion of the second run @64M FFT  I had been doing both the 60M and 64M runs on hardware hosted by David Stanfill, the 64M one was on the GIMPScrowdfunded Intel Knights Landing machine which we used for early avx512 code development. David went AWOL last spring, and Ryan has kindly agreed to also finish the 64MFFT run on hardware available to him. Restarting that one @iteration 730M, at the 60 ms/iter he is getting on the same 32core AVX512 Intel Skylake virtual machine he used to finish the 60M run, the ETC is 8 months from now. Ryan also sent me the every10Miter persistent residue savefiles (in the same kind of FFTlengthindependent bytewise format Mlucas uses for Mersennetest savefiles) for his run, so  again pending crossconfirmation via the 64M run  I have a complete chain of 107 such flles (128 Mbyte each) which can be used for any future independent confirmation of the F30 computation in distributedcomputation fashion by multiple machines, each crunching one such 10Miter subinterval and verifying the next link in the residue chain. Last fiddled with by ewmayer on 20200119 at 21:38 
20200125, 19:55  #77 
∂^{2}ω=0
Sep 2002
República de California
2·3·1,879 Posts 
@Jeppe: This is simply the basic Pépin residue ... I have Suyama cofactorPRP code based on my own custom GMPstyle bigint library also in place, but the various shortlength residues of said test for the smaller Fermats where others have done the Pépin+Suyama and published e.g. the Res64 for the latter do not agree with mine. It may simply be a difference in some convention re. generation of the residue, but I need to dig into things and determine its source before I make any public announcements re. the F30 cofactor. (And also one wants the 2nd doublecheck run at the slightly larger FFT length to finish and confirm the Pépintest results.)

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