20210529, 18:41  #1 
"David Kirkby"
Jan 2021
Althorne, Essex, UK
111000000_{2} Posts 
What determine if P1 factoring is used?
I wanted to check the RAM usage during P1 factoring, so manually reserved an exponent, for a PRP test. The exponent has no P1 factoring.
https://www.mersenne.org/report_expo...8792767&full=1 I assumed that when I run the exponent using mprime 30.6b4, using the line given by the server Code:
PRP=xxx,1,2,108792767,1,76,0,3,1 I then changed the line in worktodo.txt, to remove the 3,1 on the end, Code:
PRP=xxx,1,2,108792767,1,76,0 I'm a bit puzzled why mprime goes straight into a computationally expensive PRP test, before giving a chance to a P1 test to find a factor. Yes, I am aware I could have reserved P1 factoring, rather than a PRP test, but I'd rather make use of the P1 results, and assumed that since a P1 factoring had not been done, one would be done before starting the PRP test. I obviously have some basic misunderstanding here. Dave Last fiddled with by drkirkby on 20210529 at 18:55 
20210529, 18:50  #2 
"David Kirkby"
Jan 2021
Althorne, Essex, UK
2^{6}·7 Posts 
I see changing the line in worktodo.txt to
Code:
PRP=(aid redacted),1,2,108792767,1,76,2 Code:
[Worker #2 May 29 19:44] Optimal P1 factoring of M108792767 using up to 376832MB of memory. [Worker #2 May 29 19:44] Assuming no factors below 2^76 and 2 primality tests saved if a factor is found. [Worker #2 May 29 19:44] Optimal bounds are B1=928000, B2=55053000 [Worker #2 May 29 19:44] Chance of finding a factor is an estimated 4.73% Last fiddled with by kriesel on 20210529 at 19:00 Reason: (don't post valid assignment IDs; remembered in post one, forgot in two) 
20210529, 18:56  #3 
"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest
1011100100100_{2} Posts 
Because for some reason the server incorrectly gave an assignment with <tests_saved>=0 that time.
Which tells the client software mprime there is no point to attempting P1, don't bother. You can fix that by changing the 76,0 to 76,1 or 76,2. Or constructing a suitable Pminus1 entry preceding the PRP entry, stopping and restarting. As usual reference info! Not sure why the server seems to have gotten that one wrong. Usually it has worked. edit: Posted a summary with link to this thread, in the Official Server Problems thread. Last fiddled with by kriesel on 20210529 at 20:32 
20210529, 19:08  #4 
"David Kirkby"
Jan 2021
Althorne, Essex, UK
2^{6}·7 Posts 
I'm glad to see I am not the only one that thought it was wrong! Perhaps because I specifically requested PRP, although I'm a bit surprised.
I reserved 16 exponents for PRP tests, and every one was of the form Code:
PRP=xxx,1,2,exponent,1,76,0,3,1 Dave Last fiddled with by drkirkby on 20210529 at 19:10 
20210604, 23:22  #5 
"Alexander"
Nov 2008
The Alamo City
2^{3}·97 Posts 
If you're doing a PRP with proof, wouldn't you only save ~1 test (not 2) by finding a P1 factor, since the certification time pales in comparison to the first test?
Last fiddled with by Happy5214 on 20210604 at 23:24 Reason: Quoting relevant code block 
20210605, 11:54  #6 
Romulan Interpreter
"name field"
Jun 2011
Thailand
2^{4}×613 Posts 
Yes, when referring to P95given assignments, that is remnant from old LL age. Nowadays you only save one test and the cert time (which is about a fifth of a test, or less, depending on the power you use in generating the cert).
However, there is nothing wrong with using 2, for example, with manual P1 assignments, people (me included) use to artificially raise the number to 3, 5, etc (i.e. manually editing it), to cheat P1 bounds calculation into using a larger B1 (and if you have memory, B2 too). This way you will spend a little bit more time doing P1, but increase your chances of finding a larger factor. This is better than using a "hard" larger B1 (specified in command line or in worktodo file for gpuOwl, for example), because in this case the bound is "flexible", it depends on the exponent, it is not fixed. Last fiddled with by LaurV on 20210605 at 11:59 
20210605, 12:22  #7  
"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest
2^{2}·1,481 Posts 
Quote:
Last fiddled with by kriesel on 20210606 at 16:40 

20210605, 13:01  #8  
"David Kirkby"
Jan 2021
Althorne, Essex, UK
111000000_{2} Posts 
Quote:
a) You like hunting for factors. I know many people do, as they have a better success rate than those looking for just Mersenne primes. b) To reduce the probability of you needing to run the more computationally expensive PRP test. c) A reason I can't think of. If your only interest is finding Mersenne Prime numbers, then is it not counterproductive to run a larger range of B1 and B2? It would seem from https://www.mersenne.org/various/math.php#p1_factoring that the optimal values of B1 and B2 are worked out, based on maximising the equation Code:
chance_of_finding_factor * primality_test_cost  factoring_cost Last fiddled with by drkirkby on 20210605 at 13:02 

20210606, 13:38  #9 
Romulan Interpreter
"name field"
Jun 2011
Thailand
2650_{16} Posts 
Our motivations vary.
Our force, as a group, stays in the fact that we are different. 
20210722, 00:57  #10 
Mar 2014
2^{2}×13 Posts 
I had just peeked in to ask whether P1 factoring bounds were being set higher than they should be... I noticed today that a recent PRP assignment was doing P1 on the basis of saving two tests rather than one... and am happy to see that there was already a thread about it, and there's an easy way I might manually change an assignment to tell it it saves only 1 test.
It does seem like the default ought to be 2 for LL testers and only 1 for PRP testers. 
20210722, 01:15  #11 
If I May
"Chris Halsall"
Sep 2002
Barbados
3×17×197 Posts 

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