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Some questions from a newbie
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Hey :) Just started crunching primes recently, and have collected some questions since then that I'm hoping some of you veterans can answer
1. First of all, why are so many subprojects "cpu only"? Are the computations involved not suitable for GPUs, or is it just that there isn't a program available to do those task with a GPU?
2. Is it possible to set "number of threads" independently for each subproject? Some seem to recommend multiple threads, and some just one, but the only configuration I can find applies to all at once, which makes it awkward if you want to contribute to many of them.
3. Is it reasonable to estimate the "chance of finding a prime" from the stats here (https://www.primegrid.com/stats_genefer.php) by simply taking (completed workunits)/(primes found). (do the numbers include proof tasks?)
Thanks!  

HonzaVolunteer moderator Volunteer tester Project scientist Send message
Joined: 15 Aug 05 Posts: 1963 ID: 352 Credit: 6,420,056,055 RAC: 2,653,228

Hi :)
All good question and basically general answer would be "yes" to all.
Ad 2  for me, it makes (more) sense if one comupter is doing one subproject and different one doing something else.
Why?
Some CPU are doing better on short task, some on longer.
See recent How to optimize the number of threads form example.
Why not?
Running multiple kind of task on single computer would be probably less efficient and frankly, single compuetr has minicrule change of finding primes on several subprojects.
With single/small number of computers, I would run one subproject to find a primes, then contunie to more demanding one.
Ad 3  basically, larger the candidate, smaller the chance of finding a prime.
See also Is there a 'probability of finding a prime' listed anywhere? for examples and formula.
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mikey Send message
Joined: 17 Mar 09 Posts: 1907 ID: 37043 Credit: 831,688,438 RAC: 818,552

Hey :) Just started crunching primes recently, and have collected some questions since then that I'm hoping some of you veterans can answer
2. Is it possible to set "number of threads" independently for each subproject? Some seem to recommend multiple threads, and some just one, but the only configuration I can find applies to all at once, which makes it awkward if you want to contribute to many of them.
Thanks!
Yes just use the 'venues' ie default or blank, home, school, work, and then all the Planets if you have enough pc's and want to have each pc running a different subproject. BUT as was said before focusing on one subproject at a time is much easier and more likely for you to find a prime number. Especially since some of the cpu only subprojects can take 150K seconds, or more, to run a single task.
It also depends on how much difference there is between your pc's, if they are close in how long they take to crunch a task then putting them in the same venue makes alot of sense, but if you have ie a dual core and an 16 core pc it might more sense to split them to get the most efficiency out of each of them. It's alot of trial and error but some of the long time crunchers here can help you with figuring out how to optimize your crunching.  

Yves GallotVolunteer developer Project scientist Send message
Joined: 19 Aug 12 Posts: 843 ID: 164101 Credit: 306,554,426 RAC: 5,458

3. Is it reasonable to estimate the "chance of finding a prime" from the stats here (https://www.primegrid.com/stats_genefer.php) by simply taking (completed workunits)/(primes found). (do the numbers include proof tasks?)
Yes but a mathematical result can also be applied: the expected number of WUs is e^{γ} log N / log p_{max},
where γ is Euler's constant, N the tested number and p_{max} the sieve limit that can be found here for GFN.
For the GFN in progress, we have
15 8,100
16 15,400
17 29,600
18 52,000
19 97,000
20 181,000
21 335,000
22 609,000
DYFL 673,000 Note that the likelihood of success is 50% for log 2 ~ 0.693147 times the expected number of WUs.
The number of GFN17 primes is about #WUs / 29,600 but less than 20,500 tasks are needed for half of the participants.
That's because few unlucky searchers need more than 50,000 or even 100,000 tasks.  

mikey Send message
Joined: 17 Mar 09 Posts: 1907 ID: 37043 Credit: 831,688,438 RAC: 818,552

For the GFN in progress, we have
DYFL 673,000
That's ALOT of DYFL tasks in progress!!!  

compositeVolunteer tester Send message
Joined: 16 Feb 10 Posts: 1172 ID: 55391 Credit: 1,221,586,795 RAC: 1,513,610

For the GFN in progress, we have
DYFL 673,000
That's ALOT of DYFL tasks in progress!!!
I think you misunderstood.
The "GFN in progress" means the kinds of subprojects available to work on.
The table shows the number of workunits expected to be processed before finding a prime in that subproject.  


I agree with most of what is said. That in mind, there are a couple of subprojects that do work OK together with the same number of threads, because the sizes of the work are similar. One examples of this is CUL and WOO.
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My lucky numbers are 121*2^45538991 and 3756801695685*2^666669±1
My movie https://vimeo.com/manage/videos/502242  

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