Search found 2051 matches

by jaap
Wed Jul 26, 2017 12:06 pm UTC
Forum: Mathematics
Topic: Determining line of sight over time
Replies: 30
Views: 3214

Re: Determining line of sight over time

By the way, having the observers moving instead of stationary does not change the difficulty of this question. Are you dropping the implicit assumption that the objects in the space are stationary? I guess so, because I never really thought of the objects as stationary. *since the line end points r...
by jaap
Wed Jul 26, 2017 5:21 am UTC
Forum: Mathematics
Topic: Determining line of sight over time
Replies: 30
Views: 3214

Re: Determining line of sight over time

Sure. I'm trying to understand the point? Do you think her/his problem is solvable? The OP is not clear: If both points are stationary is it trivial to determine whether or not they can see each other. However, both points are moving. As you said, and I agree, that part is still essentially trivial...
by jaap
Tue Jul 25, 2017 2:40 pm UTC
Forum: Mathematics
Topic: Determining line of sight over time
Replies: 30
Views: 3214

Re: Determining line of sight over time

There are two points in a space. The space is filled with objects. If both points are stationary is it trivial to determine whether or not they can see each other. However, both points are moving. Luckily, they are moving in straight lines with a constant speed. How would I go about determining at ...
by jaap
Mon Jul 24, 2017 11:57 am UTC
Forum: Logic Puzzles
Topic: Arithmetic puzzle
Replies: 5
Views: 2487

Re: Arithmetic puzzle

It is not possible.

For n>1 we have:
log n! < log nn = n log n < n2

So n! always has fewer than n2 digits (except for 1! and 0!).
by jaap
Fri Jul 21, 2017 12:28 pm UTC
Forum: Logic Puzzles
Topic: Isosceles triangles and circles : puzzle connection
Replies: 15
Views: 1637

Re: Isosceles triangles and circles : puzzle connection

Read what was written in the picture : "At right you have samples of isosceles triangles connecting three circles" Is there any precision about right triangle or not? no. So triangles could be right or not. Just watch carefully my examples : you have right triangles and not right triangle...
by jaap
Sun Jul 16, 2017 5:27 pm UTC
Forum: Movies and TV Shows
Topic: Doctor Whom
Replies: 4894
Views: 565240

Re: Doctor Whom

charliepanayi wrote:We have a female Doctor

Jodie Whittaker
by jaap
Fri Jul 07, 2017 7:52 am UTC
Forum: Language/Linguistics
Topic: How to write in plain language
Replies: 32
Views: 2723

Re: How to write in plain language

Are you getting that 20 words/sentence average from your personal digital copy? I admit that is an awful lot. On the other hand, by Shane Snow's calculations , Hemingway's books have an overall Flesch-Kincaid reading level of 4, and reading ease of a startling 95. So clearly it matters which metric...
by jaap
Sun Jul 02, 2017 1:24 pm UTC
Forum: Language/Linguistics
Topic: Regional Dialect and Idiolect Oddities (pronunciation)
Replies: 851
Views: 187053

Re: Regional Dialect and Idiolect Oddities (pronunciation)

Question: Here in the US decimal numbers are written with a "decimal point " as e.g. 3.14, which is said out loud as "three point one four". I know that in some (many?) other countries decimals are written using a comma as 3,14. In this case how is the number said out loud? Is i...
by jaap
Sat May 27, 2017 5:29 am UTC
Forum: Language/Linguistics
Topic: “good big”
Replies: 7
Views: 1599

Re: “good big”

See also this language log post. It mentions some examples where the most common word order defies categorization, e.g. "ugly little"/"big ugly".
by jaap
Tue May 02, 2017 2:57 pm UTC
Forum: Mathematics
Topic: Halting Problem
Replies: 200
Views: 13681

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...
by jaap
Thu Apr 27, 2017 7:22 am UTC
Forum: Coding
Topic: Coding: Fleeting Thoughts
Replies: 9762
Views: 1570633

Re: Coding: Fleeting Thoughts

Microsoft Powerpoint is Turing complete:
https://www.youtube.com/watch?v=uNjxe8ShM-8
by jaap
Wed Apr 12, 2017 12:24 pm UTC
Forum: Logic Puzzles
Topic: Two secrets
Replies: 20
Views: 4763

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...
by jaap
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: 1700

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?
by jaap
Thu Mar 30, 2017 9:23 am UTC
Forum: Mathematics
Topic: Futurama Puzzle Game
Replies: 5
Views: 2143

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...
by jaap
Mon Mar 06, 2017 12:42 pm UTC
Forum: Science
Topic: How can we experminetly determine the acceleration due to gravity?
Replies: 20
Views: 3202

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, ...
by jaap
Thu Mar 02, 2017 9:35 am UTC
Forum: Logic Puzzles
Topic: Escape the Frictionless Circle
Replies: 156
Views: 30284

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?
by jaap
Thu Feb 02, 2017 3:26 pm UTC
Forum: Science
Topic: Coincidence in Tycho's Model of the Solar System
Replies: 6
Views: 2022

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...
by jaap
Wed Feb 01, 2017 4:22 pm UTC
Forum: Science
Topic: Newton's shell theorem with negative mass
Replies: 12
Views: 2348

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 ...
by jaap
Mon Jan 30, 2017 1:23 pm UTC
Forum: Science
Topic: Explosions and Unobtainium, as pertains to video game physics
Replies: 9
Views: 2149

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 ...
by jaap
Wed Jan 11, 2017 4:44 pm UTC
Forum: Movies and TV Shows
Topic: Star Wars Episode VIII naming contest
Replies: 35
Views: 5260

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...
by jaap
Tue Dec 13, 2016 4:44 pm UTC
Forum: Logic Puzzles
Topic: Word Puzzle.
Replies: 6
Views: 2889

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...
by jaap
Sun Dec 04, 2016 12:49 pm UTC
Forum: Language/Linguistics
Topic: Simple Writer poetry for the Holiday Season
Replies: 11
Views: 3958

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...
by jaap
Wed Nov 16, 2016 7:01 am UTC
Forum: Science
Topic: V=IR - bad science or am I being thick?
Replies: 15
Views: 3424

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 ...
by jaap
Sat Oct 22, 2016 4:39 pm UTC
Forum: Mathematics
Topic: Primes under different moduli
Replies: 4
Views: 1921

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...
by jaap
Mon Oct 10, 2016 2:12 pm UTC
Forum: Science
Topic: V=IR - bad science or am I being thick?
Replies: 15
Views: 3424

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...
by jaap
Tue Oct 04, 2016 5:51 pm UTC
Forum: Logic Puzzles
Topic: Maya Cosmic Number Puzzles
Replies: 5
Views: 3052

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 ...
by jaap
Tue Oct 04, 2016 8:51 am UTC
Forum: Language/Linguistics
Topic: Why are some linguistic patterns irritating?
Replies: 59
Views: 9548

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.
by jaap
Mon Sep 19, 2016 7:28 am UTC
Forum: Language/Linguistics
Topic: Think Before Naming Your Child
Replies: 1622
Views: 282575

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...
by jaap
Thu Sep 01, 2016 4:34 pm UTC
Forum: Mathematics
Topic: How to Calculate Pi without a Calculator?
Replies: 66
Views: 8759

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...
by jaap
Wed Aug 31, 2016 12:15 pm UTC
Forum: Language/Linguistics
Topic: Annoying words, and Words You Hate
Replies: 1931
Views: 366830

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...
by jaap
Tue Aug 30, 2016 8:17 am UTC
Forum: Science
Topic: What is the Biggest Non-Repeating Molecule?
Replies: 39
Views: 6509

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...
by jaap
Mon Aug 29, 2016 3:01 pm UTC
Forum: Mathematics
Topic: How to Calculate Pi without a Calculator?
Replies: 66
Views: 8759

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...
by jaap
Sun Aug 28, 2016 3:41 pm UTC
Forum: Mathematics
Topic: Goahead52's Math Posts
Replies: 148
Views: 12335

Re: Goahead52's Math Posts

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...
by jaap
Sun Aug 28, 2016 1:05 pm UTC
Forum: Mathematics
Topic: Goahead52's Math Posts
Replies: 148
Views: 12335

Re: Goahead52's Math Posts

(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....
by jaap
Thu Aug 25, 2016 7:49 pm UTC
Forum: Language/Linguistics
Topic: Miscellaneous language questions
Replies: 510
Views: 48756

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...
by jaap
Thu Aug 25, 2016 3:31 pm UTC
Forum: Mathematics
Topic: How to Calculate Pi without a Calculator?
Replies: 66
Views: 8759

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...
by jaap
Sat Aug 20, 2016 10:33 am UTC
Forum: Mathematics
Topic: Please help, crazy example :-(
Replies: 9
Views: 2295

Re: Please help, crazy example :-(

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...
by jaap
Fri Aug 19, 2016 2:23 pm UTC
Forum: Mathematics
Topic: How to Calculate Pi without a Calculator?
Replies: 66
Views: 8759

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...
by jaap
Tue Aug 16, 2016 12:08 pm UTC
Forum: Computer Science
Topic: Deliberately bad algorithms
Replies: 120
Views: 34239

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).
by jaap
Tue Aug 16, 2016 11:06 am UTC
Forum: Coding
Topic: Coding: Fleeting Thoughts
Replies: 9762
Views: 1570633

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...

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