20090407, 23:18  #45 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
10054_{10} Posts 
Even smaller, which are for example 98105 digit SNFS jobs.
Don't forget SNFS jobs. They are fun, and a good excercise for the mind (to build a polynomial in some cases; in most cases of course  it's a boring excercise for boring polynomials). Some Fibonacci numbers have very nice polynomials, and so do e.g. numbers of form a^13n+b^13n, and Aurifeuillians and so on, and so on. In those 98105 digit SNFS jobs, if you will have oversieved (using 0.4 or 0.5), the filtering will fail to converge and the script will stop (it's fixable, too,  check the similar threads). If you use 0.2 with those jobs, you will converge in a ridiculously short time, like 5 or 10 minutes for the whole factorization. Like this one: Code:
n: 142636039930449499515055724706069369122952024169034908419840194033346894320140545970889557 c4: 7 c0: 11 Y1: 1 Y0: 10000000000000000000000000 skew: 1.12 type: snfs lss: 1 rlim: 400000 alim: 400000 lpbr: 25 lpba: 25 mfbr: 45 mfba: 45 rlambda: 2.2 alambda: 2.2 Compare that to the times of mpqs or gnfs. 
20090407, 23:26  #46 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
2·11·457 Posts 
...or take this one for example (someone couldn't quite finish it)...
Code:
n: 7126956154329172964190407581733579595542753084022720093873577878288167714232922899398415101 m: 200000000000000000000000000 deg: 4 c4: 13 c0: 44 skew: 1.36 type: snfs lss: 1 rlim: 410000 alim: 410000 lpbr: 25 lpba: 25 mfbr: 45 mfba: 45 rlambda: 2.2 alambda: 2.2 Last fiddled with by Batalov on 20090407 at 23:36 
20090408, 00:11  #47  
A Sunny Moo
Aug 2007
USA (GMT5)
1869_{16} Posts 
Quote:
I ended up finishing it with factLat.pl after postprocessing with msieve just wouldn't work no matter how much relations I limited it to. I got the window between "filtering wants more relations" and "matrix not dense enough" down to a window of 100 relations, and it still wouldn't work, so I gave up and did it with factLat.pl. (Note: this was done with an unmodified factMsieve.pl, downloaded a month or so ago. I really should update to the latest newandimproved one some time soon...not sure if it would help in this particular instance though.) Last fiddled with by mdettweiler on 20090408 at 00:12 

20090408, 00:30  #48  
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
10011101000110_{2} Posts 
Quote:
You know what could have happened with your trimming? msieve adds "free" rels. if you trim these away, nothing will change in the next filtering run  they will be simply added back in. Ok, and here's a trick from the bottom of my sack. 1. trim .dat file and also 2. edit the .job file! decrease by 10 the "q0" that's there. This is necessary to deceive the siever not to sieve, because otherwise it will sieve a bunch again and you will have trimmed in vain. This necessary number of relations (MINRELS) is so tricky that no one really wants to touch this 0.2 parameter in the downloadable script! At the very least 0.2 works almost always (if only not for this number). Here's the necessary magic to finish fiascos like this (trimming extra relations from the bottom of the .dat file... but not too many ... how many is not too many? nobody really knows!)  http://mersenneforum.org/showthread.php?t=11585 and bits of the same advice in three or four more threads... This does plague little numbers and not medium and large numbers. If you are working on a dayweek scale jobs, then 0.5 is the coefficient you almost always need. the MINRELS.txt patch was supposed to help (mostly for larger numbers); but if the number is tiny, then put 1 in the MINRELS.txt file  that shouldn't hurt. Last fiddled with by Batalov on 20090408 at 00:48 

20090408, 01:54  #49  
A Sunny Moo
Aug 2007
USA (GMT5)
3·2,083 Posts 
Quote:
Regarding the little trick of "fooling" factMsieve.pl into not sieving any more: yes, I've used that a few times. However, in this case it wasn't necessary since, in reality, I was simply running msieve directly (though with the exact same command line that factMsieve.pl had originally tried to feed to it, with modifications where necessary to make it chop off additional relations). 

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