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Distributed.net Finds Optimal 25-Mark Golomb Ruler

timothy posted more than 5 years ago | from the unique-and-in-duplicate dept.

Math 265

kpearson writes "Distributed.net's 8-year-old OGR-25 distributed computing project has just proven conclusively that the predicted shortest 25-mark Golomb ruler is optimal. 'The total length of the ruler is 480, with marks at positions: 0 12 29 39 72 91 146 157 160 161 166 191 207 214 258 290 316 354 372 394 396 431 459 467 480. (This ruler may alternatively be expressed in terms of the distance between those positions, which is how dnetc displays them: 12-17-10-33-19-...).' 124,387 people participated in the project and two people found the shortest ruler, one on October 10, 2007 and the other on March 24, 2008."

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What (1, Funny)

Anonymous Coward | more than 5 years ago | (#25513685)

What

Not Bush? (1, Troll)

erroneus (253617) | more than 5 years ago | (#25513687)

Does this mean the optimum ruler is not Bush?

Re:Not Bush? (4, Funny)

tepples (727027) | more than 5 years ago | (#25513713)

It means the optimum ruler is Gollum.

Re:Not Bush? (0)

Anonymous Coward | more than 5 years ago | (#25513967)

That is only true when he has the Golomb Ring.

wtf (5, Insightful)

Anonymous Coward | more than 5 years ago | (#25513693)

i know we're all supposed to be nerds here, but this is way left of field. dont supposed you could have included a LITTLE more info in the summary as to what the fuck you're talking about?

Re:wtf (0, Insightful)

Anonymous Coward | more than 5 years ago | (#25513921)

Click on the 4th link?

Shouldn't have to (4, Insightful)

ArchieBunker (132337) | more than 5 years ago | (#25514019)

Headlines or summaries should be self explanatory.

Hello, context??? (5, Insightful)

schamberlin (1354695) | more than 5 years ago | (#25514103)

That's got to be the most incomprehensible story summary I've ever seen posted to Slashdot, and that's saying a lot. Seriously. The predicted shortest 25-mark Golomb ruler is optimal? What on earth are you talking about? How about giving us the barest minimum of a context, so we might have some tiny clue what that spew of buzzwords is getting at.

Re:Hello, context??? (3, Insightful)

Anonymous Coward | more than 5 years ago | (#25514337)

You really can't get more specific than that. Just because you don't know what a Golomb ruler isn't doesn't make it a bad summary. A summary has to assume some understanding of the subject at hand. If a summary includes mention of a photon, for example, it doesn't necessarily require that it be defined what a photon is in the summary.

Re:Hello, context??? (4, Insightful)

Galactic Dominator (944134) | more than 5 years ago | (#25514475)

A summary has to assume some understanding of the subject at hand. If a summary includes mention of a photon, for example, it doesn't necessarily require that it be defined what a photon is in the summary.

That's the point of the criticism. A large majority of the readers here would be familiar with a photon, but not with a Golomb ruler.

Re:Hello, context??? (-1, Troll)

Anonymous Coward | more than 5 years ago | (#25514523)

Should there be a quantum mechanics primer in the summary of every quantum computing article?

Re:Hello, context??? (0)

Ngarrang (1023425) | more than 5 years ago | (#25514671)

And those that do not know should hand in their geek card and stop reading slashdot.

Re:Hello, context??? (1)

Hal_Porter (817932) | more than 5 years ago | (#25514547)

Hopefully DHS agents will decide it is terrorist code and waterboard the submitter whilst asking him questions like "WHO IS GOLLUM?!", "WHAT IS OCR24?!" and the ever popular "WHO ARE YOU WORKING FOR?"

Re:Hello, context??? (0)

Anonymous Coward | more than 5 years ago | (#25514595)

lmfao!!!

Re:Hello, context??? (3, Funny)

this great guy (922511) | more than 5 years ago | (#25514651)

The words "Golomb ruler" are displayed in a dark green color by your browser. Placing the mouse pointer over them usually transforms it in a hand. This is called an "hyperlink", or more commonly, "link". By clicking on it, you are redirected to a page from a site called "Wikipedia", a free, multilingual online encyclopedia project. This page explains what a Golomb ruler is. HTH.

Re:wtf (5, Informative)

Anonymous Coward | more than 5 years ago | (#25514021)

According to the wikipedia article that was linked, a Golomb ruler is a set of numbers where no two pairs of numbers have the same distance. The "order" is how many numbers are in it, and the "optimal" ruler for an order is the one that ends on the lowest number.

So what they've found which set of 25 numbers - where the distance between any possible pair among them is unique - ends on the lowest number.

Re:wtf (4, Funny)

kestasjk (933987) | more than 5 years ago | (#25514473)

Pfff, 25-mark. Wake me up when they get the 26-mark. </unimpressedslashdotuser>

Re:wtf (1, Insightful)

Anonymous Coward | more than 5 years ago | (#25514663)

take note editors. it would not have been difficult to include something along the lines of the OPs first paragraph to make the summary read like an article, instead of a steaming pile of shit

Why the hell does Gollum need a ruler anyway? (5, Funny)

unassimilatible (225662) | more than 5 years ago | (#25514495)

The sumbitch spends most of his time in a dark cave.

And what the hell would he measure anyway? Not like he has any windows for drapes, my precious.

Re:Why the hell does Gollum need a ruler anyway? (4, Funny)

Bruce Perens (3872) | more than 5 years ago | (#25514601)

They should call them Precious Gollum Rulers.

cool! (-1, Troll)

Anonymous Coward | more than 5 years ago | (#25513699)

A couple weeks ago, while browsing around the library downtown, I had to take a piss. As I entered the john, Barack Obama -- the messiah himself -- came out of one of the booths. I stood at the urinal looking at him out of the corner of my eye as he washed his hands. He didn't once look at me. He was busy and in any case I was sure the secret service wouldn't even let me shake his hand.

As soon as he left I darted into the booth he'd vacated, hoping there might be a lingering smell of shit and even a seat still warm from his sturdy ass. I found not only the smell but the shit itself. He'd forgotten to flush. And what a treasure he had left behind. Three or four beautiful specimens floated in the bowl. It apparently had been a fairly dry, constipated shit, for all were fat, stiff, and ruggedly textured. The real prize was a great feast of turd -- a nine inch gastrointestinal triumph as thick as his cock -- or at least as I imagined it!

I knelt before the bowl, inhaling the rich brown fragrance and wondered if I should obey the impulse building up inside me. I'd always been a liberal democrat and had been on the Obama train since last year. Of course I'd had fantasies of meeting him, sucking his cock and balls, not to mention sucking his asshole clean, but I never imagined I would have the chance. Now, here I was, confronted with the most beautiful five-pound turd I'd ever feasted my eyes on, a sausage fit to star in any fantasy and one I knew to have been hatched from the asshole of Barack Obama, the chosen one.

Why not? I plucked it from the bowl, holding it with both hands to keep it from breaking. I lifted it to my nose. It smelled like rich, ripe limburger (horrid, but thrilling), yet had the consistency of cheddar. What is cheese anyway but milk turning to shit without the benefit of a digestive tract?

I gave it a lick and found that it tasted better then it smelled.

I hesitated no longer. I shoved the fucking thing as far into my mouth as I could get it and sucked on it like a big half nigger cock, beating my meat like a madman. I wanted to completely engulf it and bit off a large chunk, flooding my mouth with the intense, bittersweet flavor. To my delight I found that while the water in the bowl had chilled the outside of the turd, it was still warm inside. As I chewed I discovered that it was filled with hard little bits of something I soon identified as peanuts. He hadn't chewed them carefully and they'd passed through his body virtually unchanged. I ate it greedily, sending lump after peanutty lump sliding scratchily down my throat. My only regret was that Barack Obama wasn't there to see my loyalty and wash it down with his piss.

I soon reached a terrific climax. I caught my cum in the cupped palm of my hand and drank it down. Believe me, there is no more delightful combination of flavors than the hot sweetness of cum with the rich bitterness of shit. It's even better than listening to an Obama speech!

Afterwards I was sorry that I hadn't made it last longer. But then I realized that I still had a lot of fun in store for me. There was still a clutch of virile turds left in the bowl. I tenderly fished them out, rolled them into my handkerchief, and stashed them in my briefcase. In the week to come I found all kinds of ways to eat the shit without bolting it right down. Once eaten it's gone forever unless you want to filch it third hand out of your own asshole. Not an unreasonable recourse in moments of desperation or simple boredom.

I stored the turds in the refrigerator when I was not using them but within a week they were all gone. The last one I held in my mouth without chewing, letting it slowly dissolve. I had liquid shit trickling down my throat for nearly four hours. I must have had six orgasms in the process.

I often think of Barack Obama dropping solid gold out of his sweet, pink asshole every day, never knowing what joy it could, and at least once did, bring to a grateful democrat.

Re:cool! (5, Funny)

Dermah (1277738) | more than 5 years ago | (#25514365)

I was expecting you to measure the shit with a Golomb ruler. Oh well.

Story (0, Offtopic)

RobDollar (1137885) | more than 5 years ago | (#25513755)

jsut to nip in there quickly, and this is effectively irrelavent, why the hell is everything tagged "story"? Tags are annoying enough without it, but at least (tagging beta) has gone, that was driving me nuts.

Re:Story (0)

Anonymous Coward | more than 5 years ago | (#25513827)

jsut to nip in there quickly, and this is effectively irrelavent, why the hell is everything tagged "story"?

Tags are annoying enough without it, but at least (tagging beta) has gone, that was driving me nuts.

Uh, it's one small row of text. (tagging beta) was a few characters within a small row of text. What type of OCD do you need to be driven nuts by that?

Re:Story (1)

philspear (1142299) | more than 5 years ago | (#25513911)

The type of OCD that makes one check /.

Re:Story (1)

johanatan (1159309) | more than 5 years ago | (#25514007)

Umm... 6 * 12oz > 40oz

Are you saying Bush has helped wean you off alcohol? Maybe it's because he's been there himself and you feel some sort of mystical connection to the man? :-)

Re:Story (1)

philspear (1142299) | more than 5 years ago | (#25514115)

Umm... 6 * 12oz > 40oz

That's true not only in terms of volume, but also price (it's an economy joke).

Re:Story (1)

larry bagina (561269) | more than 5 years ago | (#25514467)

after 8 years of Obama, will you be Joe MD 20-20 or Joe Colt 45?

Re:Story (5, Insightful)

Raenex (947668) | more than 5 years ago | (#25513995)

why the hell is everything tagged "story"?

I have another question. What happened to the option to turn off tags?

And one more: Is there any forum to discuss Slashdot issues? Seems like the only way is to bitch off-topic in the articles.

Re:Story (0, Troll)

RobDollar (1137885) | more than 5 years ago | (#25514279)

Touche, although in this reply you have somewhat contradicted your aim. Catch 22 I guess. Everyone loves an annoying cunt anyway.

Re:Story (5, Funny)

Todd Fisher (680265) | more than 5 years ago | (#25514563)

A forum!? You can take your fancy Web 2.0 "community" fad elsewhere. We've got Golomb rulers to discuss here!

Re:Story (5, Informative)

_xeno_ (155264) | more than 5 years ago | (#25514629)

why the hell is everything tagged "story"?

If you mouse over it (and have JavaScript enabled), you'll be informed that it's the "type tag." I assume the concept is that it differentiates between journals, comments, bookmarks, feed entries, and other types of nodes that could, conceptually, appear in the firehose [slashdot.org] .

I have no idea why Slashdot feels the need to show these on the main page, though, considering that everything that currently shows on the main page is a story. But if you play with the firehose, it's what tells you what "thing" the entry is.

Sounds like an American's attempt at a meter stick (0)

Anonymous Coward | more than 5 years ago | (#25513777)

Someone on TV said there are 352 feet in a yard [youtube.com] . Since a meter is a little more than a yard, I guess 480 sounds about right.

proved? (0)

socsoc (1116769) | more than 5 years ago | (#25513809)

I thought you could only disprove, not prove math stuff...

Did I fail math class?

Re:proved? (5, Insightful)

martin-boundary (547041) | more than 5 years ago | (#25513823)

Did I fail math class?

Yes. Yes, you did.

Re:proved? (5, Funny)

philspear (1142299) | more than 5 years ago | (#25513923)

But you can't prove that, which proves his point.

Re:proved? (1)

sunami (751539) | more than 5 years ago | (#25514113)

But you can't prove that, which proves his point.

*HEAD ASPLODE*

Re:proved? (-1, Offtopic)

Tycho (11893) | more than 5 years ago | (#25514645)

Yeah, but the winner of the first season of "Survivor", Richard Hatch, has managed to perform several examples of epic fail related to math, among other types of fail. For instance, he could not determine the result for 11*11 and choose an incorrect result on the Australian version of "Who Wants to Be a Millionaire?" This was the fourth question posed to him, so he walked away with nothing. Perhaps more damaging was that Hatch did not report his cash prize for winning "Survivor" to the IRS. Eventually the IRS noticed a problem in Hatch's returns, as one should always expect from the IRS and should surprise no one. In general, reporting discrepancies that are of a reasonable size will be investigated, especially those related to larger sized amounts, like Hatch did. As Hatch went through the legal system, he had several more instances of fail. These fail were mostly of the legal variety, IIRC he did manage have a lawyer and was unable to use frivolous tax avoidance arguments. Due to Hatch taking this approach, his lawyer avoided sanctions, like disbarment, and Hatch, avoided fines of up to $5000 for each instance, which can and are assessed regularly in Tax Court. In any case, the threat of disbarment, means that wacky discredited legal theories will not be used by defense lawyers who want to continue on their current career path. In any case, Hatch ended up with a sentence of 4 years, 3 months, and will not spend his time in a maximum security facility. Hatch has a release date of October 2009. However, something that may negate any benefits of a lower security level is that Hatch is now idiling his time away at a prison, in an armpit of a state, West Virginia.

Re:proved? (1)

Cyberax (705495) | more than 5 years ago | (#25513825)

Yes.

Re:proved? (0)

Anonymous Coward | more than 5 years ago | (#25513845)

Remember that little chat we had about you confusing Science with Religion? Yeah. It applies here.

Re:proved? (1)

gardyloo (512791) | more than 5 years ago | (#25513847)

Apparently so.

Re:proved? (0)

Anonymous Coward | more than 5 years ago | (#25513851)

yes, yes you did.

Re:proved? (4, Insightful)

gardyloo (512791) | more than 5 years ago | (#25513855)

Mathematics may be defined
as the subject in which we
never know what we are talking
about,nor whether what we are
saying is true.
--Bertrand Russell

Re:proved? (1)

johanatan (1159309) | more than 5 years ago | (#25514017)

I would ask a man who makes a statement such as that to 'prove' it.

Re:proved? (1)

msuarezalvarez (667058) | more than 5 years ago | (#25514237)

And pretty much everyone who gets the fact that Russel was making what amounts to essentially a joke in this context would ignore you...

Re:proved? (3, Insightful)

Futile Rhetoric (1105323) | more than 5 years ago | (#25514447)

Hasn't GÃdel done pretty much exactly that? [wikipedia.org]

Re:proved? (1)

e9th (652576) | more than 5 years ago | (#25514463)

Hey Bert, we need to talk about that Principia Mathematica thing.
Your pal, Kurt Godel.

Re:proved? (5, Informative)

bunratty (545641) | more than 5 years ago | (#25513867)

You're thinking of science. You can only disprove a hypothesis, never prove it true. In math, you can prove or disprove a conjecture.

Re:proved? (1)

socsoc (1116769) | more than 5 years ago | (#25513889)

thanks for the one real answer.... /where's my beer

Re:proved? (0, Offtopic)

johanatan (1159309) | more than 5 years ago | (#25514033)

Well, the be fair, the ones who answered 'yes' gave correct answers too. :-)

Re:proved? (1)

socsoc (1116769) | more than 5 years ago | (#25514061)

Yeah... I meant the one "hey drunk guy, I think this is what you meant" answer.

apologies to all the yes men and for the record, my TI-89 did all the math for me...

Re:proved? (0, Offtopic)

johanatan (1159309) | more than 5 years ago | (#25514137)

I know. His answer was definitely more helpful than 'yes'. :-) [Though I think he should've added:

In math, you can prove or disprove a conjecture [based on certain axioms (i.e., assumptions)]

Re:proved? (5, Informative)

Anonymous Coward | more than 5 years ago | (#25513943)

What most people don't realize is that all of mathematics is based on certain assumptions, alternatively called axioms, postulates or definitions. Do all triangles have interior angles that add up to 180 degrees? Yes, but only if you make certain assumptions. That's called Euclidean geometry. There is also non-Euclidean geometry which is equally valid and is used to describe some systems in reality. Is there no highest prime? Does 2 + 2 = 4? Do parallel lines never intersect? Are no circles square? Yes again on all counts, but only if you make certain assumptions. So when we say that "x is proven" in mathematics then that is really shorthand for "x is proven based on certain assumptions". That doesn't stop some overzealous mathematicians from acting a little bit smug. I would like to point all smug mathematicians to Kurt Godel's incompleteness theorems.

Re:proved? (1)

johanatan (1159309) | more than 5 years ago | (#25514091)

Awesome point! I went through a lengthy argument with some mathematicians on here recently about cardinalities of infinite sets (specifically N, Q and the set of all primes). Their proofs of the equalities of these cardinalities (in my [and the finitist] opinion) are based some rather dubious assumptions (although there are subtle distinctions between my position and that of the finitist).

Re:proved? (1)

msuarezalvarez (667058) | more than 5 years ago | (#25514259)

Assumptions cannot be dubious.

They may be not of your liking, but that hardly makes them dubious.

Re:proved? (4, Funny)

Merls the Sneaky (1031058) | more than 5 years ago | (#25514197)

You just reminded me of......

Ah, Kryten; just thinking. [Rapidly] Assuming of course we're not dealing with five-dimensional objects in a basic Euclidean geometric universe and given the essential premise that all geo-mathematics is based on the hideously limiting notion that one plus one equals two, and not as Astemeyer correctly postulates that one and two are in fact the same thing observed from different precepts, (Pulls a "nerdy" grimace, and loudly exhales through his nose.) the theoretical shape described by Siddus must therefore be a poly-dri-doc-deca-wee-hedron-a-hexa-sexa-hedro-adicon-a-di-bi-dolly-he-deca-dodron. (Pulls the same face, exhales a second time.) Everything else is poppycock. Isn't that so?

+1, Red Dwarf (0)

Anonymous Coward | more than 5 years ago | (#25514443)

nt

Re:proved? (2, Insightful)

panda cakes (1333537) | more than 5 years ago | (#25514245)

You are confused - there are no assumptions in mathematics because mathematics does not deal with any real entities. There are only definitions and what you are talking about applies to them: depending on your definitions properties of defined entities will differ. Quite a trivial conclusion most sane people already realize.

Re:proved? (1)

blue l0g1c (1007517) | more than 5 years ago | (#25514109)

Ah yes, the aptly-named "proof."

whatcouldpossiblygowrong (1, Funny)

IceCreamGuy (904648) | more than 5 years ago | (#25513871)

I like how this is tagged "whatcouldpossiblygowrong," as if building a better radio antenna is going to bring about the end of the world. Oh, wait, I forgot that the movie "Pulse" was a documentary...

Re:whatcouldpossiblygowrong (1)

philspear (1142299) | more than 5 years ago | (#25513955)

It's always a valid if stupid question. What could go wrong? In this case, the 25-mark Golomb ruler may NOT be optimal, in which case you would have people using the 25-mark Golomb ruler, with... gasp... SUB optimal results. You might be asking yourself what that would look like. I really haven't the slightest idea what any of this is about, so I couldn't say.

But the tag gets onto any and all biology related articles, along with it's brother "iamlegend." Usually when it has nothing to do with curing cancer with dangerous viruses. A finding that DNA sequences prefer to associate with similar sequences? Some bright person asked whatcouldpossiblygowrong. The answer there is: nothing.

Wha-? (0)

Anonymous Coward | more than 5 years ago | (#25513873)

I didn't RTFA, but going by the headline I would say this must be spam. It sounds exactly like some of the stuff in my spam folder. You know, "Russian bedroom casino wisdom embarrassment", and the like.

Oh crap, I'm not supposed to reply to spam.

What will be their next project? (4, Interesting)

Anonymous Coward | more than 5 years ago | (#25513891)

distributed.net used to have a very vibrant community, with several projects on-going at one time. But lately, things haven't been going so well for them. The prize funds for their RC5-72 challenge were recently yanked. And the only other project they had on-going was this OGR-25 project.

Does anyone know if they'll offer further projects in the near future? Many people I know have moved on to BOINC-based [berkeley.edu] distributed computing projects, instead of sticking with distributed.net.

Re:What will be their next project? (1, Informative)

Anonymous Coward | more than 5 years ago | (#25514067)

They are still offering the prize money, just not from RSA.

And they are going to begin OGR-26 soon.

so we get cheaper, better antennas? (3, Insightful)

ClintJCL (264898) | more than 5 years ago | (#25513931)

The Wikipedia page says One practical use of Golomb rulers is in the design of phased array radio antennas such as radio telescopes. Antennas in an [0,1,4,6] Golomb ruler configuration can often be seen at cell sites [wikipedia.org] . Does this mean we can now construct larger antennas with greater sensing power, using fewer materials, due to knowing a larger optimal configuration than previously?

Re:so we get cheaper, better antennas? (4, Informative)

Pinckney (1098477) | more than 5 years ago | (#25513987)

Probably not. The [0,1,4,6] ruler is only order 4; we've previously known optimal rulers up to order 23. If larger configurations can be practically used, I would expect to see order 5 and higher already in use.

Re:so we get cheaper, better antennas? (2, Insightful)

mblase (200735) | more than 5 years ago | (#25513991)

Does this mean we can now construct larger antennas with greater sensing power, using fewer materials, due to knowing a larger optimal configuration than previously?

Probably not, since (a) optimal rulers of order greater than four but less than twenty have been known for some time, and (b) the [0,1,4,6] ruler is proven to be the largest perfect optimal ruler (according to the Wikipedia article).

Re:so we get cheaper, better antennas? (1)

ClintJCL (264898) | more than 5 years ago | (#25514065)

Thank you. So being "perfect" helps more in this situation than anything else?

Re:so we get cheaper, better antennas? (3, Informative)

Jsprat23 (148634) | more than 5 years ago | (#25514173)

As a hypothesis, if the distance from 0 to 1 is half a wavelength, the distance from 1 to 4 is 3/2 wavelengths and the distance from 1 to 6 is 5/2 wavelengths. These distances represent the first 3 resonances of a resonant dipole antenna. In the case of an antenna, perfect would mean capturing all of the resonances and thus be optimal.

very interesting (1)

ClintJCL (264898) | more than 5 years ago | (#25514411)

I don't get how they know which resonances are the perfect ones to capture, though... Did someone just arbitrarily decide that? Does this coincide with music theory at all (octaves, harmonics, etc)?

Re:so we get cheaper, better antennas? (1)

oljanx (1318801) | more than 5 years ago | (#25514255)

the [0,1,4,6] ruler is proven to be the largest perfect optimal ruler (according to the Wikipedia article)

I'm not seeing that on en.wikipepdia, anyone know where I can take a look at that proof? Is it simple enough for someone to explain quickly?

Re:so we get cheaper, better antennas? (1, Informative)

Free the Cowards (1280296) | more than 5 years ago | (#25514503)

Wikipedia says:

There is no requirement that a Golomb ruler can measure all distances up to its length, but if it does, it is called a perfect Golomb ruler. It has been proven that no perfect Golomb ruler exists for five or more marks.

And then links to a page which contains the proof.

Re:so we get cheaper, better antennas? (1)

SQLGuru (980662) | more than 5 years ago | (#25514003)

Partly yes and partly no. (disclaimer, I only know what I read on Wikipedia -- much like you)

It sounds like an optimal Golomb ruler allows you to find the shortest that works (which would imply less materials [towers?]) but in this case, it was merely confirming the one that was already assumed to be the shortest. So, yes but no.

Layne

Re:so we get cheaper, better antennas? (4, Informative)

mabhatter654 (561290) | more than 5 years ago | (#25514231)

it's essentially defines a list of numbers such that if you pick any two segments that are not the same segment they will always have different lengths. This is useful for things that involve harmonics.. radio, buildings, ect. where you need to build "imperfect" shapes. With antennas this is so that they don't interfere with each other in close proximity. With bridges you might need to make each length of bridge section a slightly different length to keep the bridge from vibrating to pieces. It's a list, highly useful to engineers of various types. Not that exciting, unless you really needed to have 25 critical measurements when 24 just wouldn't do.

can someone please tell me which #s aren't incl? (1, Interesting)

ClintJCL (264898) | more than 5 years ago | (#25514027)

Every number I plugged in could be measured as a length between 2 numbers in that set. But according to wikipedia, no perfect ruler exists for over 5. And this has 25. So it's not perfect.

So does anyone have a list of numbers that can't be measured as distances between these? I'd rather not calculate it myself.

Re:can someone please tell me which #s aren't incl (2, Informative)

Anonymous Coward | more than 5 years ago | (#25514167)

A few lines of Python suggests that there are 180 numbers that can't be measured, starting with 81, 90, 93, 103, 110...

Obviously the 11 numbers preceding 480 can't be measured, for example.

Re:can someone please tell me which #s aren't incl (2, Insightful)

Pretzalzz (577309) | more than 5 years ago | (#25514185)

Well, 25 choose 2 is 300 so presumably 180 numbers must be missing.

Re:can someone please tell me which #s aren't incl (1)

cavePrisoner (1184997) | more than 5 years ago | (#25514189)

479 is one if I understand the problem correctly

Re:can someone please tell me which #s aren't incl (1)

interiot (50685) | more than 5 years ago | (#25514203)

Missing are: 81, 90, 93, 103, ... 476, 477, 478, 479 (180 different numbers missing total). The fact that it can measure all distances from 1 to 25 doesn't make it perfect, it has to measure all distances up to its length (480).

Re:can someone please tell me which #s aren't incl (1)

TBoon (1381891) | more than 5 years ago | (#25514205)

For starters, with 25 stops, there is 300 distances, so there has to be some numbers missing. To find which ones, I filled all the numbers into a spreadsheet, calculated the length/difference between all numbers, and then put that all together and sorted them. The lowest missing number is 81.

If you tried starting at the other end, you would have gotten results much quicker. Everything from 469 to 479 is missing. (Quite obvious actually, as the second and second-last numbers are 12/13 away from the ends.)

It hasn't been proven, it has been shown. (0)

Secret Rabbit (914973) | more than 5 years ago | (#25514079)

There is a BIG difference between the two as anyone within the Maths and the Sciences can tell you. I'm sorry, but people routinely get this wrong and it gets quite aggravating.

Re:It hasn't been proven, it has been shown. (5, Insightful)

gardyloo (512791) | more than 5 years ago | (#25514243)

Yes, people routinely get this wrong. They're not wrong this time.

  In this case, the distinction between "it was proven" and "it was shown" is a distinction without a difference. In math, you can "show" something within a restricted domain; for example, that a postulated solution to a given equation really is a solution, without giving a complete family of solutions. One can show it numerically, or show it analytically. Here, a restricted set of postulated solutions over the only available domain (the positive integers) was exhaustively searched for actual solutions, and the set that satisfied the postulates was also shown to be optimal (in a well-defined sense for the problem).

    This is no more a "non-proof" than the proof of the 4-color map theorem in two dimensions, which was also "shown" using an exhaustive search.

Bah, Humbug! (4, Insightful)

Main Gauche (881147) | more than 5 years ago | (#25514303)

There is a BIG difference between [proven and shown] as anyone within the Maths and the Sciences can tell you. I'm sorry, but people routinely get this wrong and it gets quite aggravating.

First, there is such a thing as proof by inspection. It may be considered inelegant by certain folks, but it's there nonetheless.

Second, it's just as aggravating (for those in certain fields) that computational results are not more valued. Sure, analytical results provide insight that computational results do not. But if you simply want to know the answer, why not accept a computational result?

Third, anticipating the old "how do we know the computer didn't make a mistake" comment: Theoretical proofs need to be proofread just as code does. So why not accept a computer program (and its verified output, as in the summary) as proof?

That's enough of a proof (4, Informative)

khchung (462899) | more than 5 years ago | (#25514483)

I am sorry, but listing out all possibilities (assuming that's what they did) and showing one is the minimum IS a valid proof for that minimum in that particular case.

For example, to prove "7 is a prime number", listing out 1,2,3,4,5,6 and then showing all are not a factor of 7 is a valid proof that "7 is a prime number". If you think this is not a proof, tell me which step in the proof is wrong.

Of course, whether the proof of Distributed.net is correct depends on how strongly they can prove their program actually covered all possibilities.

Re:That's enough of a proof (1)

stinerman (812158) | more than 5 years ago | (#25514623)

Certainly.

The proof, however, is not very elegant. Unfortunately, brute force is the best tool we have for certain "hard" problems.

Re:That's enough of a proof (1, Informative)

Anonymous Coward | more than 5 years ago | (#25514675)

It is an NP problem, so as long as they tried all possibilities, it should be correct.

Moo! (0)

22_9_3_11_25 (645799) | more than 5 years ago | (#25514099)

Great news!

I would really like to understand this. (1)

ArbitraryDescriptor (1257752) | more than 5 years ago | (#25514123)

I read the article on OGR-25. I read the wikipedia article. The Fine article is sadly slashdotted, and I am still at a loss as to why this is useful, or.. difficult? I'm kind of at a total loss, if you want to get down to it.

Could a valid and perfect ruler not be made in the form of 0,1,3,6,10,15,21,28,36,etc to infinity?
Would it not be shorter than 480?
I'm clearly misunderstanding both requisite criteria and ultimate application; any help there would be appreciated.

no two pairs can be the same distance apart (1, Insightful)

schamberlin (1354695) | more than 5 years ago | (#25514149)

In your example, the distance between 0 and 3 is the same as between 3 and 6. Not a Golomb ruler.

Re:I would really like to understand this. (0)

ArbitraryDescriptor (1257752) | more than 5 years ago | (#25514159)

Oh, wait. It just filtered through. No 3 points are the same distance apart. Beer and mathematical constructs way above my pay grade are not the greatest of chums.

Re:I would really like to understand this. (0)

Anonymous Coward | more than 5 years ago | (#25514187)

A Golumb Ruler is not as simple as your example. The distance between any two points can not be the same. In your example the difference from 0 to 6 is 6.. 15 to 21 is 6. Therefore this is not a Golumb Ruler.

Re:I would really like to understand this. (1)

Paco103 (758133) | more than 5 years ago | (#25514219)

no two pairs of marks are the same distance apart

0,3 -> Distance 3
3,6 -> Distance 3

0,6 -> Distance 6
15,21 -> Distance 6

That's where the problem comes. As you ad more numbers, sequences that were previously valid Golumb rulers are no longer because distances are repeates. It's not just the length between any adjacent pairs that cannot be repeated.

That being said, it's still hard to understand why we care. As has been pointed out above, we haven't found any practical use for any sequences above 5. Maybe someday we will though.

Re:I would really like to understand this. (3, Informative)

mabhatter654 (561290) | more than 5 years ago | (#25514305)

the application has to do with harmonics. For example the classic problem is that bridge that collapsed under wind load in the 40's. It collapsed partly because harmonics from the wind, just like a whistle, built up. Part of breaking harmonics is having a quick list of numbers that you can be sure won't duplicate. In a bridge you might pick your structural members to be just a little "off" using proportions from this list so that no two pieces were identical, one way of reducing vibrations in the structure.

Each length appears exactly once on the list and they can never be repeated unless you pick the exact same line segment.

Re:I would really like to understand this. (1)

Fex303 (557896) | more than 5 years ago | (#25514653)

Could a valid and perfect ruler not be made in the form of 0,1,3,6,10,15,21,28,36,etc to infinity?

No. Because the ruler looks at the distances between ALL the various makes on it. So in your example, it's invalid because the distance between 0 and 3 is 3 and the distance between 3 and 6 is 3. (Same issues with 0,6 and 15,21, etc.) You're aiming to find something where no two points are the same distance apart, not just adjacent points.

That said, I'm just going off the wikipedia article myself too, so if someone who knows better than me cares to comment, feel free to jump in.

I can do better than that... (4, Funny)

pottymouth (61296) | more than 5 years ago | (#25514153)

My new yumiz ruler is perfectly calibrated in emh's and is 14.667 long. Now I'm going to go measure something like the how many pins can fit on one you guy's heads...

wut? (1)

slyborg (524607) | more than 5 years ago | (#25514385)

parser: no such token "yumiz"
parser: no such token "emh's"
parser: all you pins are like the belong to us

I put a few hundred hours into distributed net (1)

mrflash818 (226638) | more than 5 years ago | (#25514299)

As then my work PC could keep my toes warm :)

I'd like to RTFA... (0)

Aeternitas827 (1256210) | more than 5 years ago | (#25514317)

But it seems they can't quite handle it right now:

Sorry, but the slashdot effect is just too much for us to handle
with this perl .cgi script.
Moo. ]:8)

The cow was a nice touch, though.

bitches (-1, Troll)

Anonymous Coward | more than 5 years ago | (#25514351)

now you got your nigger president. can we finally end the state sponsored racism known as equal opportunity? fucking that fucking racism shit.

Mathematically, this sounds like an excellent (1)

mmell (832646) | more than 5 years ago | (#25514691)

candidate for use in an encryption scheme. Problems of class NP are especially useful in this area.
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