0356: "Nerd Sniping"

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0356: "Nerd Sniping"

Postby iNap » Wed Dec 12, 2007 5:13 am UTC

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http://xkcd.com/356/
Alt: I first saw this problem on the Google Labs Aptitude Test. A professor and I filled a blackboard without getting anywhere. Have fun.

What about engineers, though? Should I be worried?

For that matter, I'm majoring in EE. Should I be worried about this guy in particular?
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Re: "Nerd Sniping" Discussion

Postby Cabhan » Wed Dec 12, 2007 5:15 am UTC

I'm Computer Science, but I can imagine this happening. Something about LL(1) languages. I shall now be forever warier.
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Re: "Nerd Sniping" Discussion

Postby Number3Pencils » Wed Dec 12, 2007 5:17 am UTC

Absolutely hilarious. Reminds me of Alan Mendelsohn's "missile whistle" from Alan Mendelsohn, the Boy from Mars. He shoots an incredibly loud whistle right at someone's head, and as they turn in astonishment, they adjust their course just slightly and run smack into a trash can.
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Re: "Nerd Sniping" Discussion

Postby chardish » Wed Dec 12, 2007 5:17 am UTC

Gosh, I want to say that it's infinite. That'd be too easy though, right?
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Re: "Nerd Sniping" Discussion

Postby athelas » Wed Dec 12, 2007 5:18 am UTC

Reaction mechanisms. Actually, I kind of want a really hard problem, just to chew on when I'm bored.
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Re: "Nerd Sniping" Discussion

Postby Lobstrosity » Wed Dec 12, 2007 5:19 am UTC

One thing I never liked about this comic is how it excludes "Literary Nerds", if you will.

i.e. "Which is a better literary work, Stephen Crain's "Open Boat" or Ralph Waldo Emerson's "Self Reliance"?"
Last edited by Lobstrosity on Wed Dec 12, 2007 5:27 am UTC, edited 1 time in total.
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Re: "Nerd Sniping" Discussion

Postby DragonMudd » Wed Dec 12, 2007 5:22 am UTC

I'm a physicist and I had that problem on my Math Methods final... never could figure out what it had to do with anything that we covered in that class (complex analysis, crazy PDEs and other continuous stuff).
Last edited by DragonMudd on Wed Dec 12, 2007 5:35 am UTC, edited 1 time in total.
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Re: "Nerd Sniping" Discussion

Postby ++$_ » Wed Dec 12, 2007 5:23 am UTC

I'd be posting in this thread, but I'm busy thinking about the problem instead.
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Re: "Nerd Sniping" Discussion

Postby theyellowhobbit » Wed Dec 12, 2007 5:25 am UTC

Lobstrosity wrote:One thing I never liked about this comic is how it excludes "Literary Nerds", if you will.

In this case it's a good thing. We're smart enough not to get hit by trucks...

(Though I'm more archaeology/religion nerd, but it's the same principle. Though I suppose a shiny artifact would have the same effect on me...)
aleflamedyud wrote:I think you just made my "Impossible-But-Awesome-O-Meter" blow up.
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Re: "Nerd Sniping" Discussion

Postby erl137 » Wed Dec 12, 2007 5:28 am UTC

It looks like a preturbative problem to me . . . of course, I'm not as clear on the technical end of that as I'd like, so, somebody please feel free to correct me.
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Re: "Nerd Sniping" Discussion

Postby Lobstrosity » Wed Dec 12, 2007 5:30 am UTC

theyellowhobbit wrote:In this case it's a good thing. We're smart enough not to get hit by trucks...

(Though I'm more archaeology/religion nerd, but it's the same principle. Though I suppose a shiny artifact would have the same effect on me...)


Agreed. But I guess this comic just made me think in general, all of the comics. I guess the description of the comic excludes literature though. Only language... (A webcomic of romance, sarcasm, math, and language.)
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Re: "Nerd Sniping" Discussion

Postby Aleril » Wed Dec 12, 2007 5:30 am UTC

Hee

I think I am the only person here who didnt even bother with the problem because I dont know anything about it.

Good comic though
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Re: "Nerd Sniping" Discussion

Postby Trella » Wed Dec 12, 2007 5:33 am UTC

I also didn't even bother :P
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Re: "Nerd Sniping" Discussion

Postby vwlou89 » Wed Dec 12, 2007 5:33 am UTC

Wouldn't the resistance be 0? I actually came up with a number that would satisfy this in my Calculus class: 1-.99999... It comes out to .000...0001 (infinite zeros). It can be represented as "the limit of y such that y=1/x as x goes to infinity". Since it could never really reach zero it would be as close to zero as was possible. Just a thought.
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Re: "Nerd Sniping" Discussion

Postby Jorpho » Wed Dec 12, 2007 5:35 am UTC

Ah, reminds me a lot of this old Story Minute comic. (I first saw it on a professor's door, with the last panel's caption replaced by "And then he went to graduate school...")

I love those old Story Minute bits; a shame the books are out of print.
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Re: "Nerd Sniping" Discussion

Postby Kleppner » Wed Dec 12, 2007 5:35 am UTC

Why can I see my professor making this a question on my final exam.
(Yes, they do actually read XKCD!)
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Re: "Nerd Sniping" Discussion

Postby theyellowhobbit » Wed Dec 12, 2007 5:37 am UTC

Aleril wrote:Hee

I think I am the only person here who didnt even bother with the problem because I dont know anything about it.

Good comic though



I didn't bother with it either.
aleflamedyud wrote:I think you just made my "Impossible-But-Awesome-O-Meter" blow up.
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Re: "Nerd Sniping" Discussion

Postby phlip » Wed Dec 12, 2007 5:38 am UTC

chardish wrote:Gosh, I want to say that it's infinite. That'd be too easy though, right?

I would say it'd have to be less than three ohms... since there's a 3 ohm path between the two nodes, and adding extra, parallel paths, can only make the resistance less...

Also... is it a bad sign that, despite the entire setup of the strip warning me about it, I still almost stopped reading the strip in the middle and started trying to solve the puzzle, before I realised what I was doing, and finished reading the strip?

vwlou89: Please don't bring up the 0.999... = 1 thing again... I'm still recovering from last time.
While no one overhear you quickly tell me not cow cow.
but how about watch phone?
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Re: "Nerd Sniping" Discussion

Postby ptveite » Wed Dec 12, 2007 5:39 am UTC

Wow, the more I think about it, the cooler/more disgusting this problem becomes.
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Re: "Nerd Sniping" Discussion

Postby ep103 » Wed Dec 12, 2007 5:40 am UTC

w00t its 2/pi ohms!
http://answers.google.com/answers/threadview?id=92564

Now get moving before you all get hit by trucks
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Re: "Nerd Sniping" Discussion

Postby vwlou89 » Wed Dec 12, 2007 5:41 am UTC

phlip wrote:vwlou89: Please don't bring up the 0.999... = 1 thing again... I'm still recovering from last time.


Will do...i really don't mean to instigate argument (yet it always happens) it just seems like such a convenient but totally hypothetical number and it kind of makes sense in this case.
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Re: "Nerd Sniping" Discussion

Postby DragonHawk » Wed Dec 12, 2007 5:42 am UTC

Oh-oh. This could be dangerous. I suspect this is doing to be one busy thread.

(under breath: Let's see, resistance is cumulative in series, but an inverse ratio in parallel... the grid is infinite, so we've got an unlimited number of both types... though the parallel paths will always also have some series paths, but there are series paths without any parallel elements... I wonder if that could lead to a canceling effect, making for a "neater" answer... but maybe not, and looking for that is red herring... hmmmm.... looks at clock Yikes. Okay, punt.)

I have discovered a truly marvelous answer to this, which this post is too small to contain... ;-)
Last edited by DragonHawk on Wed Dec 12, 2007 5:43 am UTC, edited 1 time in total.
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Re: "Nerd Sniping" Discussion

Postby Chimo » Wed Dec 12, 2007 5:43 am UTC

Hmm... is this by any chance the Classhole? (http://xkcd.com/72/ for those of you who don't remember) I mean, he's got a top hat and everything. This latest endeavor seems to suit him.
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Re: "Nerd Sniping" Discussion

Postby phlip » Wed Dec 12, 2007 5:44 am UTC

ep103 wrote:w00t its 2/pi ohms!
http://answers.google.com/answers/threadview?id=92564

Now get moving before you all get hit by trucks

Hmm... unless I'm misreading that page, isn't that for just across one diagonal? ie, the diagonal across a 2x2 square of nodes?

The comic has the diagonal across a 2x3 rectangle of nodes...
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Re: "Nerd Sniping" Discussion

Postby DragonMudd » Wed Dec 12, 2007 5:44 am UTC

ep103 wrote:w00t its 2/pi ohms!
http://answers.google.com/answers/threadview?id=92564

Now get moving before you all get hit by trucks


Good find, but that's not quite the same problem. The one you found was across a single diagonal... this one is from a Knight's move. Maybe 3/pi?

Edit: Dang... just a bit too slow.
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Re: "Nerd Sniping" Discussion

Postby Hit3k » Wed Dec 12, 2007 5:46 am UTC

Ah resistors, thy mortal enemy. I always had trouble working out resistance in physics when doing electricity. but what you've really got to ask yourself is: Are they in series or parallel?

I'm just a bit... drugged up on medicine at the moment.. I don't know if I make any sense or not.
Last edited by Hit3k on Wed Dec 12, 2007 5:48 am UTC, edited 1 time in total.
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Re: "Nerd Sniping" Discussion

Postby floyd4one » Wed Dec 12, 2007 5:46 am UTC

erl137 wrote:It looks like a preturbative problem to me . . . of course, I'm not as clear on the technical end of that as I'd like, so, somebody please feel free to correct me.


Actually this problem is solved using a 2D Fourier series. I'm guessing the answer is between 2/pi Ohms and 8/3pi Ohms (the solutions between 1 diagonal and 2 diagonal points away respectively)

Runs off to play with Mathematica.... Yes I am a physicist.

Edit: Here's the solution if you want to check yourself :P
Spoiler:
The answer is 4/pi-.5 Ohms == .773 Ohms.
As I predicted the resistance is between the other two cases which are numerically .637 and .849 Ohms.
Last edited by floyd4one on Wed Dec 12, 2007 5:57 am UTC, edited 3 times in total.
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Re: "Nerd Sniping" Discussion

Postby aerojad » Wed Dec 12, 2007 5:47 am UTC

in before the group tries to figure it out!
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Re: "Nerd Sniping" Discussion

Postby ep103 » Wed Dec 12, 2007 5:50 am UTC

I didn't have time to read the derivation, as I need to get studying for a non-ece final I have in 8 hours, but...
if the solution I did find is only for a single square diagonal, can't we assume that since this is an infinite symetrical grid, with each indidivual box having equivalent resistance, the equivalent resistance of the problem in question should be related by a simple triangle, ie,
taking the triangle formed in the single square to have signs equal to an arbitrary unit of 1,
the hyptoneuse then has a length of sqrt(2).
For the rectangle depicted here, using the same units, the hyptoneneuse will have a length of sqrt(5).
Assuming symmetry, etc, etc, we therefore have the answer here is (2/pi)*sqrt(5)/sqrt(2)...?

edit: this comes out to sqrt(10)/pi ohms
Last edited by ep103 on Wed Dec 12, 2007 5:53 am UTC, edited 1 time in total.
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Re: "Nerd Sniping" Discussion

Postby bjswift » Wed Dec 12, 2007 5:52 am UTC

I had this on my 2nd semester physics class midterm. There's a pretty simple, elegant solution to it but I don't remember what it is. Prolly somewhere on the interwebs.
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Re: "Nerd Sniping" Discussion

Postby AltoidAddict » Wed Dec 12, 2007 5:54 am UTC

Aleril wrote:Hee

I think I am the only person here who didnt even bother with the problem because I dont know anything about it.

Good comic though


I didn't bother with it because even though I had the electromagnetic unit of physics 3 years ago, I'm still traumatized by it.
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Re: "Nerd Sniping" Discussion

Postby ThatOneRedhead » Wed Dec 12, 2007 5:55 am UTC

Awww... I was working on a take home final in Complex Variables and Analysis. Now, I am imagining infinite resistance networks.

/as an EE, this problem warms my heart
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Re: "Nerd Sniping" Discussion

Postby floyd4one » Wed Dec 12, 2007 5:56 am UTC

bjswift wrote:I had this on my 2nd semester physics class midterm. There's a pretty simple, elegant solution to it but I don't remember what it is. Prolly somewhere on the interwebs.


Fermat? Is that you??

ep103 wrote:edit: this comes out to sqrt(10)/pi ohms


Oh so close but not quite right :roll:
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Re: "Nerd Sniping" Discussion

Postby chishm » Wed Dec 12, 2007 5:57 am UTC

After a brief look, I can tell you that it is between 0.5 Ohms and 1.0 Ohm. Now to find the exact value...
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Re: "Nerd Sniping" Discussion

Postby Hit3k » Wed Dec 12, 2007 5:59 am UTC

spoiler'd cause it has the answer.
Spoiler:
MathWorld wrote: 10. On an infinite, two-dimensional, rectangular lattice of 1-ohm resistors, what is the resistance between two nodes that are a knight's move away?

R[m_, n_] := 1/(2π) Integrate[1/t (1 - ((t - I)/(t + I))^(m + n) ((t - 1)/(t + 1))^Abs[m - n]), {t, 0, ∞}]

R[1, 2]

(8 - π)/(2 π)

This problem is discussed in J. Cserti's 1999 arXiv preprint. It is also discussed in The Mathematica GuideBook for Symbolics, the forthcoming fourth volume in Michael Trott's GuideBook series, the first two of which were published just last week by Springer-Verlag. The contents for all four GuideBooks, including the two not yet published, are available on the DVD distributed with the first two GuideBooks.

http://mathworld.wolfram.com/news/2004-10-13/google/ Answers to the whole GLAT[Google Labs Aptitude Test] It doesn't look that difficult..




*can now be seen running towards his computer with mathematica to try it out*
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Re: "Nerd Sniping" Discussion

Postby floyd4one » Wed Dec 12, 2007 6:03 am UTC

[quote="Hit3k"]spoiler'd cause it has the answer.
beat ya to it 8)
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Re: "Nerd Sniping" Discussion

Postby Hit3k » Wed Dec 12, 2007 6:04 am UTC

floyd4one wrote:
Hit3k wrote:spoiler'd cause it has the answer.
beat ya to it 8)


That was from mathematica. I realise you beat me too it. I thought I'd show the mathematica solution though ;)
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Re: "Nerd Sniping" Discussion

Postby floyd4one » Wed Dec 12, 2007 6:07 am UTC

Hit3k wrote:
floyd4one wrote:
Hit3k wrote:spoiler'd cause it has the answer.
beat ya to it 8)


That was from mathematica. I realise you beat me too it. I thought I'd show the mathematica solution though ;)


Showing your work is highly overrated :lol:

In fact it's that kind of extra split-second dilly-dallying that gets you hit by a bus... *zoom-zoom*
Last edited by floyd4one on Wed Dec 12, 2007 6:08 am UTC, edited 1 time in total.
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Re: "Nerd Sniping" Discussion

Postby Hit3k » Wed Dec 12, 2007 6:08 am UTC

floyd4one wrote:
Hit3k wrote:
floyd4one wrote:
Hit3k wrote:spoiler'd cause it has the answer.
beat ya to it 8)


That was from mathematica. I realise you beat me too it. I thought I'd show the mathematica solution though ;)


Showing your work is highly overrated :lol:


Thats what I said to my maths teacher[s]!
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Re: "Nerd Sniping" Discussion

Postby floyd4one » Wed Dec 12, 2007 6:11 am UTC

You know if xkcd has this kind of motivating power, Randall ought to put it to good use. For example slip in a subtle problem that is equivalent to a proof of NP-completeness or some other intractable task... within hours of being posted someone on the fora might have a solution! :shock:
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