At 12:27 AM 7/11/2002 +0100, Daran wrote: >P-1 factoring with 459MB available memory, the program chose the following >limits for these two exponants. > >7786567 B1=40000, B2=640000 >7714127 B1=40000, B2=650000 > >Why did the smaller exponant get the higher B2 limit?
The short answer is I don't know. I invite someone to figure it out. Look for the last routine in commonc.c called guess_pminus1_bounds. First off, when dealing with P-1 success vs. cost analysis, the difference between 640000 and 650000 is negligible. Possible reasons for your case: 1) The code uses inexact interpolation and numerical integration to compute Dickman's function. 2) The GCD cost for the larger exponent is higher. This should be more than offset by the cost of the extra 72440 doublechecking LL iterations. 3) There are more trial factors with the smaller exponent in a given range because factors are 1 mod 2p. The costing routine sums up the chances of finding 65 bit, 66 bit, 67 bit, etc. factors. This should be offset by the higher exponent having a better chance of finding a smooth factor (found factors are 2kp+1 where k is smooth - larger p means smaller k which means a higher chance of success). Of course, the other possibility is a nasty bug in prime95. _________________________________________________________________________ Unsubscribe & list info -- http://www.ndatech.com/mersenne/signup.htm Mersenne Prime FAQ -- http://www.tasam.com/~lrwiman/FAQ-mers
