20110328, 23:12  #1 
Dec 2010
Monticello
5×359 Posts 
TF Credit oddities
Hi:
I am running manual tests on a lowend GPU (mfaktc 0.16p1 on Galaxy GEForce210, with CUDA capability 1.2), and one core of a standard AMD 6core 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 ResultType Received agedays Result GHzDays Manual testing 82303141 NF 20110328 13:27 6.6 no factor for M82303141 from 2^68 to 2^69 [mfaktc 0.16p1Win 71bit_mul24] 0.7264 EricAMD6core 54008443 NF 20110328 18:53 2.6 no factor from 2^68 to 2^69 1.1069 Why is this? 
20110329, 00:55  #2 
Einyen
Dec 2003
Denmark
3,037 Posts 
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 20110329 at 00:57 
20110329, 02:11  #3  
"Richard B. Woods"
Aug 2002
Wisconsin USA
2^{2}×3×641 Posts 
Quote:
Between any two given powersof2, the number of candidate factors for a higher exponent is less than the number of candidate factors for a lower exponent. Thus, if the powerof2 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 20110329 at 02:33 

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