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Old 2020-03-05, 13:38   #1
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Aug 2009

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Default Riesel Prime Search

I got into the Riesel prime search early in February. There was a bit of a learning curve as to how this was done and what software needed to be used.

The main testing application, LLR, is quite straightforward. It simply requires an input file in the proper format. This is a deterministic application, which runs Lucas-Lehmer tests. I started out with PFGW. It is probabilistic, running PRP tests on candidates. For this project, the results must be absolute. No probably. Very early on, I was instructed to use LLR and not PFGW. The difference really didn't click with me at the start. It didn't take long to realize the need for LLR. I run LLR on two machines: One i7 and one i5. There is a speed difference. I have found a way to compensate for this. I wrote a small console binary which splits the sieve results into two separate files. 60% goes to the i7 and the other 40% to the i5. It works quite well. I also wrote a Windows GUI variant which performs the same exact task.

Sieving: This is still in experiment mode, more or less. I started out sieving with NewPGen. Several members here indicated that I need to be using the "sr" family of programs. These include srsieve, srsieve2, sr1sieve, and sr2sieve. These are faster. The last two have an option to run low-priority and I use it.

The question then became, "How far do I need to sieve?" Some reading in the forums indicated many had their own ways. Some like to run to a set p limit. An example would be 700e9 (700-billion). This route can be, and most often is, very time consuming. Two members I corresponded with suggested that I do this as a function of time, not size. Most sieve applications have a "removal rate," the interval in seconds at which factors are found. The longer the run, the lower the rate becomes. A removal rate of 60 seconds is much lower than a rate of 6 seconds.

The next issue was where to sieve. Running LLR and sieving on the same machine creates a significant bottleneck for LLR. Doing so added an extra 10 to 12 seconds for each n in the input file. I had a third option, a Dell laptop. It is a dual-core i5. This laptop was not designed to do this sort of work. So, it is low priority. Heat is problematic for laptops. It sits on a cooling device with five fans. This made a real difference. This is where the sieving process has nested. It is not fast, but it does a good job. I am running NewPGen on it for several reasons. One, it is a GUI application which is easy to use, and for me to see. Two, it has several options to limit the sieving time: Removal rate, p size, and the number of hours. Finally, there is no need to rush to save time for the two LLR machines. Not pushing the laptop beyond its capability is my primary concern. I do not want to shorten its life more than necessary.

And so it goes...
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