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Old 2018-02-11, 10:07   #1
king
 
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Default Can I run Prime95 on two different computers same time to test one same exponent?

Will that save time?

Does each computer automatically avoid redundant calculations?
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Old 2018-02-11, 10:11   #2
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Quote:
Originally Posted by king View Post
Can I run Prime95 on two different computers same time to test one same exponent?
Yes.
Quote:
Originally Posted by king View Post
Will that save time?
No.
Quote:
Originally Posted by king View Post
Does each computer automatically avoid redundant calculations?
No.

And it won't count as a double check either. That has to be two different computers from different people.
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Old 2018-02-11, 10:32   #3
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You would only potentially want to do that if you were doing an LL test that would many many years, as a way to detect and correct errors as they happen (otherwise that's years of computation lost). But that's not recommended now even for tests that would take years. The solution now would be to do a PRP test first (which takes roughly as long as LL and has stronger error detection, but technically doesn't prove primality), followed by LL tests if it's shown to be probably prime.
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Old 2018-02-11, 10:51   #4
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Quote:
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And it won't count as a double check either. That has to be two different computers from different people.
Now, that's new for me... I thought you could double-check your exponent using 2 different hardwares...
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Old 2018-02-11, 11:30   #5
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Quote:
Originally Posted by ET_ View Post
Now, that's new for me... I thought you could double-check your exponent using 2 different hardwares...
Makes sense to me. Easy to create "matching" tests when you have access to the full residue. It won't deter a determined individual, as it is easy to create another account.

Last fiddled with by sdbardwick on 2018-02-11 at 11:32
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Old 2018-02-11, 13:15   #6
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Quote:
Originally Posted by M344587487 View Post
...
But that's not recommended now even for tests that would take years. The solution now would be to do a PRP test first (which takes roughly as long as LL and has stronger error detection, but technically doesn't prove primality), followed by LL tests if it's shown to be probably prime.
My understanding is that once a PRP test has been done on a candidate it must be double checked by another PRP test (done by another user). Of course a LL test must be double-checked by a matching LL test. But is is a waste of time to mix PRP and LL on one candidate.

Jacob
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Old 2018-02-11, 14:59   #7
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Practically, you can't. Each step requires the result of the previous one. And to share parts of the process between 2 different machines doesn't work well. The time to communicate data between the machines would slow things down. It is much faster overall to have each machine work on a different number. Prime95 often is limited by how fast the CPU can communicate to the machine's RAM. Communication between machines is normally vastly slower than that.

There are exceptions, but the average user does not have access to the machines that are configured properly. And you would want to be running mlucas, not Prime95. (IIRC)
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Old 2018-02-11, 15:09   #8
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Quote:
Originally Posted by S485122 View Post
My understanding is that once a PRP test has been done on a candidate it must be double checked by another PRP test (done by another user). Of course a LL test must be double-checked by a matching LL test. But is is a waste of time to mix PRP and LL on one candidate.

Jacob
AFAIK a PRP results in one of two things, "composite" or "probably prime", with good odds on it being prime if the latter. If PRP shows composite, you do another PRP test to confirm, but if if it comes out probably prime it's time to do LL.
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Old 2018-02-11, 17:38   #9
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Oops !
Quote:
Originally Posted by M344587487 View Post
...
if it's shown to be probably prime.
I hadn't taken the last part of your statement with its all important "if" into account, (probably because of the low odds, but nevertheless there was an "if".)

You are completely right.

Jacob
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