mersenneforum.org P-1 B1/B2 selection with "Test=" vs "Pfactor="
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2005-03-19, 20:55   #1
James Heinrich

"James Heinrich"
May 2004
ex-Northern Ontario

E9516 Posts
P-1 B1/B2 selection with "Test=" vs "Pfactor="

Why is it that the B1/B2 bounds selected are so vastly different with the same exponent on the same machine if the P-1 test is invoked with these two different lines?
Code:
Pfactor=79299821,72,1

Test=79299821,72
The Pfactor line gives
Quote:
 B1=395000,B2=8295000, chance = 3.84%
The Test line gives
Quote:
 B1=835000,B2=21918750, chance = 5.13%
Why would Prime95 select such vastly-different bounds for the two testing methods? Whether a LL is going to be performed immediately afterwards shouldn't make any difference... should it?

 2005-03-19, 21:32 #2 garo     Aug 2002 Termonfeckin, IE 24×173 Posts Try Pfactor=79299821,72,0 The answer lies in whether a factor would save one test or two.
2005-03-19, 21:58   #3
James Heinrich

"James Heinrich"
May 2004
ex-Northern Ontario

3,733 Posts

Indeed...
Pfactor=79299821,72,0 gives the same result as Test=79299821,72

Now I better understand the documentation:
Quote:
 Pfactor=exponent,how_far_factored,has_been_LL_tested_once

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