mersenneforum.org  

Go Back   mersenneforum.org > Great Internet Mersenne Prime Search > PrimeNet

Reply
 
Thread Tools
Old 2011-03-28, 23:12   #1
Christenson
 
Christenson's Avatar
 
Dec 2010
Monticello

70316 Posts
Default TF Credit oddities

Hi:

I am running manual tests on a low-end GPU (mfaktc 0.16p1 on Galaxy GEForce210, with CUDA capability 1.2), and one core of a standard AMD 6-core CPU on a completely different machine doing TF work.

Primenet seems to be granting the CPU much more credit for easier work than the GPU, as follows from my Primenet results details report:
CPU Name Exponent Result-Type Received age-days Result GHz-Days
Manual testing 82303141 NF 2011-03-28 13:27 6.6 no factor for M82303141 from 2^68 to 2^69 [mfaktc 0.16p1-Win 71bit_mul24] 0.7264
Eric-AMD-6-core 54008443 NF 2011-03-28 18:53 2.6 no factor from 2^68 to 2^69 1.1069

Why is this?
Christenson is offline   Reply With Quote
Old 2011-03-29, 00:55   #2
ATH
Einyen
 
ATH's Avatar
 
Dec 2003
Denmark

55 Posts
Default

You are testing factors of the form 2*k*p, so for p=82303141 it is less work to factor to 2^69 than for p=54008443:

82303141: k = 2^69 / 2*82303141 = 3,586,107,426,682
54008443: k = 2^69 / 2*54008443 = 5,464,847,508,738

0.7264 credits * 82303141/54008443 = 1,10696 credits.

Last fiddled with by ATH on 2011-03-29 at 00:57
ATH is offline   Reply With Quote
Old 2011-03-29, 02:11   #3
cheesehead
 
cheesehead's Avatar
 
"Richard B. Woods"
Aug 2002
Wisconsin USA

11110000011002 Posts
Default

Quote:
Originally Posted by Christenson View Post
Primenet seems to be granting the CPU much more credit for easier work than the GPU, as follows from my Primenet results details report:
CPU Name Exponent Result-Type Received age-days Result GHz-Days
Manual testing 82303141 NF 2011-03-28 13:27 6.6 no factor for M82303141 from 2^68 to 2^69 [mfaktc 0.16p1-Win 71bit_mul24] 0.7264
Eric-AMD-6-core 54008443 NF 2011-03-28 18:53 2.6 no factor from 2^68 to 2^69 1.1069

Why is this?
As ATH's example illustrates, for TF (unlike other factoring methods, seemingly, at first glance) the work gets "easier" as exponents go higher.

Between any two given powers-of-2, the number of candidate factors for a higher exponent is less than the number of candidate factors for a lower exponent. Thus, if the power-of-2 limits are held constant, TF has fewer and fewer candidates to test as exponents go higher.

There is an O(log exponent) factor in the time needed for each candidate test as exponents go higher, but it is swamped by the 1/n decrease in number of candidates during that progression.

Last fiddled with by cheesehead on 2011-03-29 at 02:33
cheesehead is offline   Reply With Quote
Reply

Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Oddities in large P-1 candidates clowns789 Lone Mersenne Hunters 2 2019-06-08 17:20
What does the gHz credit actually mean? mack Information & Answers 5 2009-12-17 10:41
v4 Credit on v5 precius1 Information & Answers 3 2008-11-03 22:23
MSieve oddities.... schickel Msieve 4 2007-04-15 21:42
Oddities of democracy kwstone Soap Box 3 2004-02-01 19:03

All times are UTC. The time now is 23:15.

Sat May 8 23:15:47 UTC 2021 up 30 days, 17:56, 0 users, load averages: 3.98, 4.10, 3.59

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.

This forum has received and complied with 0 (zero) government requests for information.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.
A copy of the license is included in the FAQ.