Hello, If any body is there out interesting in this topic, I found an interesting post which suggest it's possible to get this sequence of numbers empirically...
http://jeffreystedfast.blogspot.com/2007/02/shell-sort.html Ok, according to this post, this prime set is a good optimization for the increment table of the Shell Sort algorithm. Also Jeffrey Stedfast, autor of the post is contributor of Mono. I think I'm watching a circle closing here... well, I now know where to keep looking. On 17 dic, 14:18, Theraot <[email protected]> wrote: > Hello, > > Recently I've been looking at HashSet and HashTable implementations in > Mono, and I've found some code to generate prime numbers as a helper > for the algorithms, it uses a pre-calculated array of primes. This > array skips a few primes, while I think that for the use of this > primes that are close in the code may be somehow hit the performance, > I don't understand in general what was the criteria of skipping > primes. > > The array contains the following numbers: > > 11, 19, 37, 73, 109, 163, 251, 367, 557, 823, 1237, 1861, 2777, 4177, > 6247, 9371, 14057, 21089, 31627, 47431, 71143, 106721, 160073, 240101, > 360163 > > and some times, also: > > 540217, 810343, 1215497, 1823231, 2734867, 4102283, 6153409, 9230113, > 13845163 > > I've found that this same array also exists other projects under > Apache software fundation, among other places. > > My question is if this some arcane knowledge of why skip certain > primes forever lost in the ancient library of alexandria, preserved > for the even more arcane habit of code reutilization known as copy- > paste, or does anybody know how did they come to this list. > > In abstract: does somebody know why this primes and no others? > > I hope I'm able to understand it when I see the explanation, I bet my > brain is not as good to abstract the pattern... > > By the way, the code for prime generation is long tested (of course, > it's in a lot of open implementation) and has been long overcame. If > you search a bit on this group the chances are of finding a little > riddle* for a fast prime generation algarothm.... so, this has nothing > to do with the algorithm, just the pre-calculated array... I just > don't want to think that skipping this primes is a defect. > > *It was one year ago (Challenge: Generate Prime Numbers). Salutes to > Ram and CK, and let's take the chance and salute Cerberus too. > > I repeate the question in case you missed it: does somebody know why > this primes and no others? > > Theraot
