## Search found 2042 matches

Tue May 02, 2017 2:57 pm UTC
Forum: Mathematics
Topic: Halting Problem
Replies: 200
Views: 6202

### Re: Halting Problem

This what I don't understand - my assumption (perhaps mistaken) is that the Oracle program must have the last move (i.e., it must say that whatever's been fed to it will halt or that what's been fed to it will loop forever). Is that assumption incorrect? That is correct. If you had a perfect Oracle...
Thu Apr 27, 2017 7:22 am UTC
Forum: Coding
Topic: Coding: Fleeting Thoughts
Replies: 9708
Views: 1451481

### Re: Coding: Fleeting Thoughts

Microsoft Powerpoint is Turing complete:
Wed Apr 12, 2017 12:24 pm UTC
Forum: Logic Puzzles
Topic: Two secrets
Replies: 20
Views: 2869

### Re: Two secrets

I think I have an O(log(N)) solution. Let A initially be {1, 2, 3, ..., N-1}. At all times, we know that at least one of the numbers is in A. Divide A into three roughly equal sets A 1 , A 2 , and A 3 , and ask about A 1 ∪ A 2 , A 1 ∪ A 3 , and A 2 ∪ A 3 . If we get a "yes" response to on...
Mon Apr 10, 2017 2:11 pm UTC
Forum: Science
Topic: Does the geographical distribution of the northern and southern hemispheres affect the rotation of the Earth?
Replies: 8
Views: 910

### Re: Does the geographical distribution of the northern and southern hemispheres affect the rotation of the Earth?

Is the biggest effect to do with moving closer/further from the poles, thereby moving mass closer/further from the axis, and changing the moment of inertia?
Thu Mar 30, 2017 9:23 am UTC
Forum: Mathematics
Topic: Futurama Puzzle Game
Replies: 5
Views: 1388

### Re: Futurama Puzzle Game

That is an interesting question. Of course, in the episode the problem was fixed by adding two people who hadn't swapped yet, which adds enough available swaps to always make it solvable. It looks like there's some parity rule that forces complete paths to have an even number of steps, but I'm not s...
Mon Mar 06, 2017 12:42 pm UTC
Forum: Science
Topic: How can we experminetly determine the acceleration due to gravity?
Replies: 20
Views: 2089

### Re: How can we experminetly determine the acceleration due to gravity?

But for an object rolling without slipping, some of the gravitational potential energy is transformed into rotational energy. If I do the calculations right, the proportion depends on the ratio of the moment of inertia of the object and the product of its mass and the square of its rolling radius, ...
Thu Mar 02, 2017 9:35 am UTC
Forum: Logic Puzzles
Topic: Escape the Frictionless Circle
Replies: 136
Views: 23048

### Re: Escape the Frictionless Circle

LaserGuy wrote:If you fall outward,

That's a big if. How do you fall outward if your feet slide inward?
Thu Feb 02, 2017 3:26 pm UTC
Forum: Science
Topic: Coincidence in Tycho's Model of the Solar System
Replies: 6
Views: 1570

### Re: Coincidence in Tycho's Model of the Solar System

The model in that video is not to scale. The gaps between the orbits of neighbouring planets in that video are all the same, whereas in actuality the distances increase further out. Because the video uses equal distances, you will get such apparent coincidences as it makes sixth planet exactly twice...
Wed Feb 01, 2017 4:22 pm UTC
Forum: Science
Topic: Newton's shell theorem with negative mass
Replies: 12
Views: 1690

### Re: Newton's shell theorem with negative mass

I actually did my doctoral dissertation on negative mass, but mostly on cosmological scales. A matched pair of positive and negative mass particles would indeed accelerate forever. This doesn't violate conservation of energy, since the negative mass has negative kinetic energy. Generalizing, a gas ...
Mon Jan 30, 2017 1:23 pm UTC
Forum: Science
Topic: Explosions and Unobtainium, as pertains to video game physics
Replies: 9
Views: 1595

### Re: Explosions and Unobtainium, as pertains to video game physics

Here's another data point. The Mythbusters tested a scene from Lethal Weapon 2: https://en.wikipedia.org/wiki/MythBusters_(2011_season)#Episode_178_.E2.80.93_.22Toilet_Bomb.22 It turns out that that a rather heavy metal bathtub can protect you from a blast that would otherwise have been lethal (180 ...
Wed Jan 11, 2017 4:44 pm UTC
Forum: Movies and TV Shows
Topic: Star Wars Episode VIII naming contest
Replies: 35
Views: 3363

### Re: Star Wars Episode VIII naming contest

Just for larfs... What is your guess about what Episode VIII will be called? I'll lay down The Ways Of The Force I think they'll want to give a three-act structure to the new trilogy, so the middle film needs to be a slightly darker one where the Empire New Order strikes back. The title will probab...
Tue Dec 13, 2016 4:44 pm UTC
Forum: Logic Puzzles
Topic: Word Puzzle.
Replies: 6
Views: 1946

### Re: Word Puzzle.

I don't think so. A quick google for "reversible words" led me to this page . I then filtered out all the ones that are not 3 letters long, and removed eel/lee due to the repeated letter. The remaining words are almost all consonant/vowel/consonant, except for: are/era ate/eta bro/orb So i...
Sun Dec 04, 2016 12:49 pm UTC
Forum: Language/Linguistics
Topic: Simple Writer poetry for the Holiday Season
Replies: 11
Views: 2807

### Re: Simple Writer poetry for the Holiday Season

If I interpret your post correctly, you don't know the mechanism of how Simple Writer works in its way of changing certain input words into red fronts. I should be grateful, if some other readers of this thread could help me to learn that mechanism. The xkcd simplewriter page seems to use the javas...
Wed Nov 16, 2016 7:01 am UTC
Forum: Science
Topic: V=IR - bad science or am I being thick?
Replies: 15
Views: 2743

### Re: V=IR - bad science or am I being thick?

The further you go to the top-left, the more reactive the elements are. Clarification: metals in the lower left are more reactive than those in the upper left. Lithium in water will fizz around enthusiastically; sodium will ignite, and it gets more exciting from potassium on down. (Francium is too ...
Sat Oct 22, 2016 4:39 pm UTC
Forum: Mathematics
Topic: Primes under different moduli
Replies: 4
Views: 1573

### Re: Primes under different moduli

So I think it was this forum where I originally learned that all primes above 3 are of the form 6k+1 or 6k+5, meaning that if you want to search for primes, you can do so 3x as efficiently as searching evey single integer. However, I'm curious about whethere there is a value better than 6 to use th...
Mon Oct 10, 2016 2:12 pm UTC
Forum: Science
Topic: V=IR - bad science or am I being thick?
Replies: 15
Views: 2743

### Re: V=IR - bad science or am I being thick?

In this article: https://www.theguardian.com/technology/2016/oct/10/samsung-how-batteries-work-smartphones-explode there is the following statement: The higher the resistance the harder the battery has to work to maintain a usable voltage and so the amount of power it can produce per charge decreas...
Tue Oct 04, 2016 5:51 pm UTC
Forum: Logic Puzzles
Topic: Maya Cosmic Number Puzzles
Replies: 5
Views: 2272

### Re: Maya Cosmic Number Puzzles

I used pen & paper. Although each step in the solve was easy, those steps are hard to spot. I needed to make lots of annotations, and it is easy to make so many that it becomes a big unreadable mess. 00 35 63 21 56 14 42 53 11 46 04 32 60 25 36 64 22 50 15 43 01 12 40 05 33 61 26 54 65 23 51 16 ...
Tue Oct 04, 2016 8:51 am UTC
Forum: Language/Linguistics
Topic: Why are some linguistic patterns irritating?
Replies: 59
Views: 6875

### Re: Why are some linguistic patterns irritating?

Angua wrote:Which word has the wrong spelling? Chomping seems to be right to me, and bit seems to be the right word for that part of the bridle...

And horses definitely do chomp on the thing.

Apparently it used to be champing at the bit, and some people insist it still is.
Mon Sep 19, 2016 7:28 am UTC
Forum: Language/Linguistics
Topic: Think Before Naming Your Child
Replies: 1622
Views: 260742

### Re: Think Before Naming Your Child

Apparently in 1974, people in the U.S. named over 280 baby girls "Latrina". Numbers were still pretty high through the 70s before falling off, though it's possible they are creeping back up. What a terrible name. Did you happen to see the same episode of TripTank as I did last night? Or i...
Thu Sep 01, 2016 4:34 pm UTC
Forum: Mathematics
Topic: How to Calculate Pi without a Calculator?
Replies: 66
Views: 6953

### Re: How to Calculate Pi without a Calculator?

Yeah, I'm on my phone (and was between classes at that point), so it would be faster for you to just google "square root long division algorithm" than for me to do it and then go to the resulting page, copy the url, and try to paste it here (I say "try" because my phone often ha...
Wed Aug 31, 2016 12:15 pm UTC
Forum: Language/Linguistics
Topic: Annoying words, and Words You Hate
Replies: 1929
Views: 340119

### Re: Annoying words, and Words You Hate

Well, it's similar to the recent construction in "Internet speak", where people will deliberately ungrammatically drop everything between "because" and the important noun/gerund/adjective they're referring to: "Stopped for an extra coffee and doughnut before work. Because M...
Tue Aug 30, 2016 8:17 am UTC
Forum: Science
Topic: What is the Biggest Non-Repeating Molecule?
Replies: 39
Views: 5081

### Re: What is the Biggest Non-Repeating Molecule?

Rotational symmetry does not prevent a crystal from being aperiodic. Periodicity is essentially just translational symmetry. After all, a helium atom is highly rotationally symmetric, but I wouldn't call it "periodic." Your right; that was my mistake. However, a picture of the cross-secti...
Mon Aug 29, 2016 3:01 pm UTC
Forum: Mathematics
Topic: How to Calculate Pi without a Calculator?
Replies: 66
Views: 6953

### Re: How to Calculate Pi without a Calculator?

Example calculation of sqrt 3: Guess 2. Divide into 3: 3/2 = 1.5 Average the two: (2 + 1.5)/2 = 1.75 Guess 1.75 Divide into 3: 3/1.75 = 1.714286571 Average the two: (1.75 + 1.714286571)/2 = 1.732428571 Guess 1.732428571. Divide into 3: 3/1.732428571 = 1.731673165 Average = 1.732079418 Iterate until...
Sun Aug 28, 2016 3:41 pm UTC
Forum: Mathematics
Replies: 148
Views: 10126

The formula you found should be: (7-1)*(1+7 2 +7 4 +...+7 2k ) is always a triangular number for any k This is true, because: Using the formula for summing geometric series, this number is S = (7-1)*(1+7 2 +7 4 +...+7 2k ) = 6*(7 2(k+1) -1)/(7 2 -1) = 6*(7...
Sun Aug 28, 2016 1:05 pm UTC
Forum: Mathematics
Replies: 148
Views: 10126

(7-1)+(7-1)*(7^2)*(1+7+7^2+...+7^k) is always a triangular number for any k k=0: (7-1)+(7-1)*(7^2)*(7^0) = 300 = 24*25/2 = Triangle(24) k=1: (7-1)+(7-1)*(7^2)*(7^0+7^1) = 2358 is not triangular. Triangle(68) = 2346, Triangle(69) = 2415 k=2: (7-1)+(7-1)*(7^2)*(7^0+7^1+7^2) = 16764 is not triangular....
Thu Aug 25, 2016 7:49 pm UTC
Forum: Language/Linguistics
Topic: Miscellaneous language questions
Replies: 376
Views: 29217

### Re: Miscellaneous language questions

I suspect it's not French or German influence, but rather that during both wars a lot of people were writing about how to restructure the world after the end of hostilities. "In the future" is the more relevant phrase in that context. More relevant relative to "in future" though...
Thu Aug 25, 2016 3:31 pm UTC
Forum: Mathematics
Topic: How to Calculate Pi without a Calculator?
Replies: 66
Views: 6953

### Re: How to Calculate Pi without a Calculator?

You are correct. I want to calculate Pi for three reasons. I need a predictable number sequence with no patterns. I am trying to learn some higher math. I think it would be interesting to see how far I can get. For a predictable sequence with no patterns (but isn't pi), you could also say, calculat...
Sat Aug 20, 2016 10:33 am UTC
Forum: Mathematics
Replies: 9
Views: 2059

Well anyway. The number of groups that can be formed is the number of permutations of 43 times the number of partitions of 43, assuming groups with identical number of nationalities but different students are distinct groups. (Which I think is a sensible assumption, given the setting.) From that nu...
Fri Aug 19, 2016 2:23 pm UTC
Forum: Mathematics
Topic: How to Calculate Pi without a Calculator?
Replies: 66
Views: 6953

### Re: How to Calculate Pi without a Calculator?

[...] The Leibniz formula is easy, probably more fun than Ramanujan's, but converges very slowly. If the purpose is "I want to do something while I'm bored in class", I would probably go with the third option. Totally agree that the Leibniz formula would be an easy and somewhat fun way to...
Tue Aug 16, 2016 12:08 pm UTC
Forum: Computer Science
Replies: 120
Views: 29285

### Re: Slowest Sorting Algorithms that Terminate

Tub wrote:
Shufflepants wrote:Eyeballing the thing seems to lead to something like O(n^n), so you might actually have created something worse than O(n!).

I don't think so. Because of Stirling's approximation of n!, I think O(n!) is slightly worse than about the same as O(nn).
Tue Aug 16, 2016 11:06 am UTC
Forum: Coding
Topic: Coding: Fleeting Thoughts
Replies: 9708
Views: 1451481

### Re: Coding: Fleeting Thoughts

I mean... what could a carriage return without a line feed even mean for a computer? Jump to the beginning of the line and overwrite the already written characters? Yes. This allowed a running console program to use the last printed line to display a status that it could continually update, e.g. by...
Fri Aug 12, 2016 12:27 pm UTC
Forum: Logic Puzzles
Topic: Sharing secret information publicly
Replies: 27
Views: 3770

### Re: Sharing secret information publicly

If this was their solution I really think that is dumb one. A has 3 cards 1,6,7 He does not know what B has. He could write down 6 numbers : 1,2,3,5,6,7 by claiming my three cards are among those 6 cards which is true B has 3 cards : 2,3,5 He will then deduce that C holds the card 4 hence he will c...
Thu Aug 11, 2016 3:37 pm UTC
Forum: Mathematics
Topic: N digit sequence within π
Replies: 12
Views: 1802

### Re: N digit sequence within π

https://en.wikipedia.org/wiki/Normal_number Pi is conjectured (but not proven) to be Normal - that all finite sequence of digits are equally likely to occur (in any base expansion). I was about to post that too. Pi is conjectured to be normal, because almost all real numbers are normal. That means ...
Sun Aug 07, 2016 7:01 pm UTC
Forum: Mathematics
Topic: Math: Fleeting Thoughts
Replies: 377
Views: 94651

### Re: Math: Fleeting Thoughts

Now dare I ask: is it possible to make a 5-chain in 4D or higher? (I promise I won't ask about properties of these constructions in non-Eucledian space :P ) Yes. Start with the same pentagon, with the two triangles folded in opposite directions, one in the positive z direction the other in the nega...
Sun Aug 07, 2016 1:29 pm UTC
Forum: Language/Linguistics
Topic: Regional Dialect and Idiolect Oddities (pronunciation)
Replies: 599
Views: 161484

### Re: Regional Dialect and Idiolect Oddities (pronunciation)

I also have this in "eschew" [ɪˈstʃʊu] and "exchequer" [ɪkˈstʃɛkɚ], though they don't count for as much since I learned them after childhood. Eschew is an odd one - I would pronounce it completely differently, like es-shoo (sorry I'm not confident in IPA). Apparently some people...
Sun Aug 07, 2016 1:09 pm UTC
Forum: Mathematics
Topic: Math: Fleeting Thoughts
Replies: 377
Views: 94651

### Re: Math: Fleeting Thoughts

Now how to go about disproving the n=5 case? Non-adjacent vertices must be a distance of sqrt(2) apart. So what you have is essentially this pentagon: right-pentagon.png The three triangles in this pentagon all have known side lengths, so the only degrees of freedom left are the angle between the t...
Sun Aug 07, 2016 7:09 am UTC
Forum: Mathematics
Topic: Math: Fleeting Thoughts
Replies: 377
Views: 94651

### Re: Math: Fleeting Thoughts

For the 3D case, the segments are unit vectors in the X, Y, and Z directions, and the oppositely-directed unit vectors -X, -Y, -Z. I think the OP is asking for the more general case where the segments are not necessarily axis-aligned. With 7 segments you'll get something more or less like this puzz...
Sat Aug 06, 2016 10:59 pm UTC
Forum: Logic Puzzles
Topic: Puzzle game I built
Replies: 1
Views: 1917

### Re: Puzzle game I built

It's basically a Lights Out variant.
Thu Jul 28, 2016 3:27 pm UTC
Forum: Movies and TV Shows
Topic: Wander Woman
Replies: 71
Views: 4940

### Re: Wonder Woman

The only movie set in WW1 I've actually watched "A Little Princess". Its actually... very rare to see a WW1 movie IMO. There are plenty of them out there. There's quite a few. A serious but recent one is: https://upload.wikimedia.org/wikipedia/en/thumb/d/da/War-horse-poster.jpg/220px-War-...
Tue Jul 26, 2016 8:39 pm UTC
Forum: Logic Puzzles
Topic: Help with picture puzzle please .....
Replies: 3
Views: 2680

### Re: Help with picture puzzle please .....

Unfortunately this is not a logic puzzle as such because what you have given us here is not quite enough to figure it out.
It turns out that when you play the game, you need to make some clicks to progress further.
Spoiler:
The two bottom corners of the paper look like they have dog-ear folds...