On Mon, 05 Oct 2009 13:03:08 -0500, Isis <isis55423@hotpop.com> wrote:
>On Mon, 05 Oct 2009 10:26:11 -0500, Othila (JBinUp@JBinUp.local) wrote:
>
>:Hello,Isis
>:
>:in this case,I chose 3% redudancy and then I moved the "Source block count" slider in order to reach the maximum "Efficiency" with the minimum number of blocks.I obtained 99.8%
>:with 17 blocks.Not the right method ?
>
>Hi Othila,
>
>Well, efficiency can mean several things:
>
>1) - One PAR2 block repairs one article, so if you need to repair five MBs worth
>of articles, five MBs of PAR2 blocks will do it. (100% repair capability)
>
>2) - Maximum number of PAR2 blocks per file ('Powers of Two Sizing Scheme' where
>each file contains twice as many PAR2 blocks as the previous file.) (100%
>capacity)
>
>3) - CPU efficiency (Do you really care how hard your machine works? Shaving a
>few seconds off your CPU time seems hardly worth it.)
>
>Your post contained 20892 yEnc articles (85 x 245 + 67).
>
>There were 18 Universal repair blocks (.vol11+7 = 18). A Universal block can go
>anywhere in the part to repair a missing yEnc article.
>
>In addition, each Universal block had six Contingent blocks attached to it.
>These Contingent blocks are not moveable and travel along with the Universal
>block they are attached to. They are only useful if they happen to land on a
>missing yEnc article.
>
>So what are the odds? We already know that you will always be able to repair up
>to 18 articles wherever they might happen to be. Let's assume that there is also
>a 19th article missing. Subtract the 18 articles from the total number of
>articles (20892 - 18) and you are left with 20874 articles. You have 108
>Contingent blocks (6 x 18), so your odds of any of those landing on that missing
>19th article are 108 in 20874, or about one chance in 200. (If you were also
>missing a 20th article, the odds of repairing_both_of them would be about one in
>200^2, or one in 4000.)
>
>All of the above assumes a random distribution of missing articles, which can be
>calculated using Poisson's formula, q.v.,
>
><http://en.wikipedia.org/wiki/Poisson_distribution
>
>Some have disagreed with me in the past, stating that missing articles are not
>randomly distributed, and so a Poisson distribution is irrelevant.
>
>I guess one person's QuickPar is another person's Poisson.
>
>Still, even if the missing articles were_not_completely random, it is unlikely
>to find very many of them residing in the same seven article-wide (your case)
>block. If you were missing articles 7 & 8 you would need two of your Universal
>blocks, each of which is seven times larger than the article it will repair.
>
>In general, I find Contingent blocks about as useful as teats on a boar hog. The
>chances of more than a few of them being useful in a single repair are akin to
>winning the lottery and getting struck and killed by lightening on your way to
>the bank to cash in your winnings.
>
>I prefer to use QuickPar's 'Powers of Two' sizing scheme, restrict block size to
>multiples of article size, set the 'Source Block Count' to maximum, and choose
>the number of blocks to create from the 'Powers of Two minus One' series, i.e.,
>1, 3, 7, 15, 31, 63, 127, 255, 511, 1023, 2047...
>
>But that's just me.
>
>Isis
A powerful mathematical discourse on statistical probability in the
world of Par repair. So - it presumably boils down to saying that
always posting the maximum number of Pars will ensure an efficacious
repair? This number is going to be a certain percentage of the whole
unrared file - I wonder what that should be? Around 10% perhaps?
Interesting that all the 'Naked' Rars are missing the Rar file
extension. However I was able to add the Rar extension and the files
then looked ok - I was able to open one and could see the file
contents displayed.
I thought for a minute that Othila had just used a file splitter like
HJ Split. I have seen this before with posts where the earlier rars
show the rar extension but the latter ones don't but nevertheless the
whole post assembles without a problem. However, I've never seen an
entire post without any file extensions before.
I must commend Othila on her/his post. I hope this is the start of an
illustrious career - presumably 'Naked' disc two will soon be on it's
way?
Regards, Hubchy
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