20181206, 02:23  #45 
If I May
"Chris Halsall"
Sep 2002
Barbados
2·5,431 Posts 

20181206, 02:29  #46  
Sep 2003
2587_{10} Posts 
Quote:
It ran for maybe 11 days on two cores and found 2 factors out of 260 attempts. On the other hand, if I was trying to do the same thing in a smaller range like, say, under 100k — namely, finding first factors of exponents with no known factors — then it's really extremely unlikely that I'd find even one factor with the equivalent time and CPU effort, because it's been searched more extensively already. On the other hand, if you look for additional factors of exponents in the sub100k range that do already have known factors, you'd have better luck, but you'd still find factors at a slower rate than in the 17M range. 

20181206, 03:12  #47  
"Curtis"
Feb 2005
Riverside, CA
7·13·61 Posts 
Quote:
You quoted a post about GMPECM, but wasn't your demonstrated factor found with Prime95? If not, what version of GMPECM uses sigmas larger than 32 bits and has a user ID? 

20181206, 03:18  #48  
"Curtis"
Feb 2005
Riverside, CA
7×13×61 Posts 
Quote:
To try to use your terrible analogy if I flip 1000 ECM "coins" and get heads every time, it's much more likely that tails doesn't exist for this size of curve than it was before I hadn't run any curves. The probability my next curve finds a factor is rather lower because I have 1000 curves' outcomes that didn't find a factor, when compared to running my first curve. 

20181206, 03:32  #49  
"6800 descendent"
Feb 2005
Colorado
1332_{8} Posts 
Quote:


20181206, 03:36  #50  
Sep 2003
13×199 Posts 
Quote:
Note: the dartboard might be a hundred feet away, and you might need a million throws and a slingshot. Or it might be a hundred miles away, and you need a trillion projectiles and a railgun and a prayer. 

20181206, 09:35  #51  
Einyen
Dec 2003
Denmark
5·683 Posts 
Quote:


20181206, 15:02  #52  
Sep 2003
13·199 Posts 
Quote:
So if you're giving 14 GB to a stage 2 that really wants terabytes, you're giving it at least a hundred times less memory than it wants, and it will take maybe many thousands of times longer to complete. Seems like a highly inefficient use of the machine. It could be tackling rightsized tasks instead. PS, For what it's worth, x1.32xlarge instances on AWS have 64 hyperthreaded cores and nearly 2 TB of memory (1952 GiB to be exact), and they cost $4/hour at current spot prices in useast2. If you need a mere 768 GiB of memory, an r5.24xlarge has that for $1/hour at spot prices (and 48 hyperthreaded cores). Various smaller options all the way down to a onecore r5.large with 16 GiB for 2 cents an hour. There are even AWS cloud machines with 12 TiB of memory and 224 cores, but those aren't available for spot or even ondemand, just for dedicated corporate inmemory databases. Give it a few years, though, and that kind of power will probably trickle down to general availability. So if there's some specific numbercrunching task that really responds well to enormous amounts of memory and can complete in a reasonable amount of time and you can splurge or pool funding, then renting is an option. 

20181206, 16:43  #53  
Nov 2008
3·13^{2} Posts 
Quote:
This is the output file...I chopped off the last 28k characters. *** GMPECM 7.0dev [configured with MPIR 2.7.0, enableasmredc] [ECM] Save file line has no equal sign after: [Tue Oct 13 22: Resuming ECM residue saved with Prime95 Input number is 4758184975...7139017727 (25596 digits) Using B1=1000000, B2=1000000000, polynomial Dickson(6), sigma=0:3673943552503015 Step 1 took 3847484ms Step 2 took 1217010ms ********** Factor found in step 2: 113574028377227867558212550573836752813871 Found prime factor of 42 digits: 113574028377227867558212550573836752813871 Proving primality of 25555 digit cofactor may take a while... Composite cofactor 

20181206, 16:45  #54 
Nov 2008
3×13^{2} Posts 

20181206, 16:46  #55  
Nov 2008
507_{10} Posts 
Quote:


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