20190509, 16:27  #1 
"William Garnett III"
Oct 2002
Bensalem, PA
2·43 Posts 
PRP versus LL first tests for Prime95 / impact on GPU factoring
Hello,
For first time tests using Prime95 if I switch from LL to PRP and the test finishes with no errors using Gerbicz error checking does this mean 100% that there will be no need in the future for a doublecheck (like GIMPS presently does with LL)? If this is a true statement then when my current LL test finishes with Prime95 I will start doing PRP for first time tests (and use the new Prime95 version to have the latest and greatest instead of using 29.4). My CPU (Dell tower Intel CPU i34150) and GPU (EVGA GeForce GTX 1050 SC Gaming 02GP46152KR 2 GB from Newegg) have been 100% reliable so I anticipate no errors anyway. 2nd question  doing the actual factoring/LL test timings on my GPU and using the math below from GIMPS website it made sense for me to go to 76 bits for GPU72.com on my video card with mfaktc when comparing to how long it takes to do 2 LL tests on my video card with CUDALucas.  factoring_cost < chance_of_finding_factor * 2 * primality_test_cost "Looking at past factoring data we see that the chance of finding a factor between 2X and 2X+1 is about 1/x."  I have changed recently and now only go up to 75 bit on my GPU because PRP on the CPU (with no errors) eliminates the need to do a 2nd test as a doublecheck in the future  is this a correct/fair interpretation? (I know this isn't an apples to apples comparison as CUDALucas on the GPU does not do PRP I believe so I am comparing to Prime95 using PRP for the initial test and not needing a 2nd future doublecheck). Plus there is no way of knowing after my 75 bit test if the actual GIMPS user later does LL or PRP (and in reality the GIMPS math formula is only valid for present state comparing GPU factoring to GPU primality testing (LL only) and separately CPU factoring to CPU primality testing (LL or PRP)). Also FYI I only use CUDALucas for manual LL doublechecking  never first time tests. Bonus question :) if anyone knows the answer  does the new Geforce 1650 get a big factoring boost like the other new cards (i.e.  how many GHZ Days per day)? My Geforce 1050 (that EVGA slightly overclocks) gets slightly over 250 GHZ Days per day.  it is nice the 1050/1650 support 300 Watt towers so can easily slide in with no power connector. Thanks for all the answers. William 
20190509, 17:13  #2 
"Composite as Heck"
Oct 2017
5^{3}·7 Posts 
There still needs to be a double check with PRP. Using PRP means that errors are greatly reduced so the need for triple checks is greatly reduced. It also makes large exponents viable to test.

20190509, 17:17  #3  
P90 years forever!
Aug 2002
Yeehaw, FL
2^{5}×3^{5} Posts 
Quote:
One is fraud. Who would bother to submit fake results? Well, for 22 years no one. This year we have our first deranged individual finding pleasure doing this. Two is programmer error. Prime95 29.4 had an bug where it would report that it had done Gerbicz checking but did not. There were also small windows where it was vulnerable to a hardware error. Does gpuOwl or prime95 29.6 have any small windows where they are vulnerable to a hardware error? Three is human error in copying/pasting manual results. We've seen this happen recently in TF results. Quote:


20190509, 17:41  #4  
Jun 2003
5^{2}×211 Posts 
Quote:


20190509, 18:18  #5 
"William Garnett III"
Oct 2002
Bensalem, PA
2×43 Posts 
Thanks for the helpful answers everyone!

20190509, 21:45  #6  
"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest
6,131 Posts 
Quote:
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There are charts for each gpu model available at James Heinrich's site, for example https://www.mersenne.ca/cudalucas.ph...n=90&mmax=1000 Or for single exponents, for example https://www.mersenne.ca/exponent/93000067 But any additional level is welcome, and there's plenty of work to go around. Whatever you don't complete, someone else is likely to get assigned. Investigate tuning your mfaktc.ini for max performance if you haven't already. Quote:
Last fiddled with by kriesel on 20190509 at 21:49 

20190514, 03:43  #7  
Serpentine Vermin Jar
Jul 2014
2^{2}·3·277 Posts 
Quote:
During my analysis, it's amazing how many machines out there had just been churning out one bad result after another, and it was only years and years later that we realized this, once they started getting doublechecks and the trend was spotted. If the Gerbicz error detecting lives up to the promise, it will definitely help out, even if we do still find mismatches down the road. Right now, LL doublechecking is pretty far behind the first time tests, and I still have my theory (with no evidence to back it up) that we've missed a prime somewhere in the < 57M range. Ultimately that's the real problem, that we may have missed something but it'll be a decade before we know. Ultimately no harm done, but still... 

20190515, 01:01  #8 
"6800 descendent"
Feb 2005
Colorado
13×53 Posts 

20190515, 04:55  #9 
Jan 2019
Florida
241 Posts 
What is the likelihood of someone completing a valid proof of the conjecture where there exists an infinite number of Mersenne Primes? What will happen to the project?
Is it necessary for the proof, if valid, contains some formula/theorem that can be exploited for generating mersenne primes? Otherwise I don't think we have anyway of knowing if we skipped a prime or not ... unless we run all those tests again. What is the likelihood two computers returns the same bad residue though? Last fiddled with by dcheuk on 20190515 at 04:56 
20190516, 14:22  #10  
"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest
6,131 Posts 
Quote:


20190516, 14:54  #11  
"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest
17F3_{16} Posts 
Quote:
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A check of the existing PRP data for GIMPS showed no coincidence of res64 values among 9945 exponents, admittedly a small sample. The methodology of 2 matching res64 results per exponent has been checked, by systematically triple checking small/fast exponents <3M, with encouraging results. Last fiddled with by kriesel on 20190516 at 14:59 

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