20070325, 18:22  #1 
Jun 2005
62_{16} Posts 
How does prime95 choose the B1 and B2 constants?
Can one read about how the todo file format is interpreted? As an experiment I tried the P1 factoring of Prime95 which I did not know it could do. With the data as given Prime95 estimates a 5.6% chance of finding a factor and takes about 205 seconds to complete  so playing around with the to do file parameters and I changed the the ...,33,1 to ...,23,2, Now Prime95 estimates a 34% chance of finding a factor and after 1010 seconds P1 found a factor in stage #2, B1=40000, B2=700000. 1625879*2^1625879+1 has a factor: 500311388963 (this factor is not found with the ...,33,1 parameter) but the next 5 exponents could not be factored. end of experiment. I have no idea what would be good B1 and B2 parameters, Maybe somebody could advise, have i jumped the gun? is P1 testing done in progressive stages? Last fiddled with by AntonVrba on 20070325 at 18:27 
20070325, 21:20  #2 
Jun 2005
175_{16} Posts 
P1 is twostaged.
First stage: If there is a factor , it will be found if has only factors below B1. Second stage: If there is a factor , it will be found if has only factors below B1, except one which can lie between B1 and B2. How to choose B1/B2? Prime95 calculates (in a very complicated formula) the best factor throughput by taking into account processor type (I guess), memory settings (stage 2 needs a lot of mem), factorworth (how many LLR tests are going to be saved by a factor, that is the final 1 in the Pfactor=... line), and up to where it has already been sieved (that's the 33: it has been sieved up to 2^33). If you tell him that you sieved up to 2^50, it will tell you that P1 isn't worth it and that you should directly LLR. If you lower the sieve value, it will raise the bounds. But that's not what one should do. Better it is to have faith in the wisdom of the MASTER, and feed the program the correct values. Tomorrow, the 33 would be a 35, for example, because we will have sieved more. But that dosn't change much. Still questions? Yours H. PS. there is a way to chose the bounds manually, by a command i won't tell you, but which is far from secret. H. 
20070401, 18:46  #3 
Jun 2003
3×5×107 Posts 
Has anyone tried P+1 or ECM?
Last fiddled with by Citrix on 20070401 at 18:46 
20070401, 18:54  #4 
Jun 2005
101110101_{2} Posts 

20070402, 18:53  #5 
Banned
"Luigi"
Aug 2002
Team Italia
3×1,619 Posts 

20070404, 04:59  #6 
Mar 2003
New Zealand
13×89 Posts 
Is it worth using higher P1 bounds than the Prime95 default, since unlike GIMPS, in this project finding a P1 factor can also speed up the sieve a little bit?
The last field of the PFactor= line is the number of LL tests saved by finding a factor. I think this should be at least 2, maybe 3. 
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