Search found 3662 matches
- Fri Nov 27, 2015 7:42 am UTC
- Forum: Science
- Topic: convert bits to J/K -- and more entropy mischief
- Replies: 14
- Views: 3032
Re: convert bits to J/K -- and more entropy mischief
FWIW, Google Calculator can do that calculation: (1 joule / kelvin) / (ln(2) * boltzmann constant) 1.04494013 × 10 23 I guess it's just a coincidence that it's within an order of magnitude of Avogadro's number: ((1 joule / kelvin) / (ln(2) * boltzmann constant)) / (avogadros number) 0.173516388 whic...
- Sat Nov 21, 2015 10:34 am UTC
- Forum: Mathematics
- Topic: Least numbers discarded when dealing cards
- Replies: 30
- Views: 6265
Re: Least numbers discarded when dealing cards
Unfortunately, converting those digit sequences to card sequences is a little tedious, and (AFAICT) you have to generate the whole 20 digit sequence before you can decide that it's invalid. Actually, you don't have to generate the whole sequence before you can decide that it's invalid; I should kno...
- Fri Nov 20, 2015 11:42 am UTC
- Forum: Mathematics
- Topic: Least numbers discarded when dealing cards
- Replies: 30
- Views: 6265
Re: Least numbers discarded when dealing cards
Am I missing something or are people way overthinking this? Just put the numbers 1 through 52 in an array and shuffle it. Dealing cards is as simple as pulling out elements starting from the first index and working your way down. The problem is that the OP's TRNG (true random number generator) only...
- Wed Nov 18, 2015 10:40 pm UTC
- Forum: Coding
- Topic: Coding: Fleeting Thoughts
- Replies: 9924
- Views: 1882381
Re: Coding: Fleeting Thoughts
Inside the electrons are quarks, [...] In the Standard Model, electrons, like all leptons , are fundamental particles in their own right, they aren't composed of quarks. Quarks (and gluons), and particles composed of quarks, feel the strong nuclear force, but leptons are oblivious to that force. Ho...
- Sat Nov 14, 2015 4:18 pm UTC
- Forum: Mathematics
- Topic: Numbers are cool. Is there a proof/theorem for this?
- Replies: 2
- Views: 1403
Re: Numbers are cool. Is there a proof/theorem for this?
This is related to the topic of perfect numbers and aliquot sequences . If we continue your sequence that starts with 62447, the next number after 15505 is 5807, which is prime, so it must be followed by 1. If we start at a perfect number, eg 6 or 28, then the next number is the same number we start...
- Fri Nov 06, 2015 7:45 am UTC
- Forum: Science
- Topic: Miscellaneous Science Questions
- Replies: 2904
- Views: 676047
Re: RELATIVITY QUESTIONS! (and other common queries)
If quantum field theory in curved space could be reasoned about successfully with fractions, I'd have gotten my PhD in fourth grade. :D If you want to know what Hawking radiation looks like to an infalling observer rather than one at infinity, just do the Bogolyubov transformation for that intrepid...
- Fri Nov 06, 2015 6:41 am UTC
- Forum: News & Articles
- Topic: In other news... (humorous news items)
- Replies: 15072
- Views: 2481000
Re: In other news... (humorous news items, etc)
Here's a pertinent quote from Yes, Minister (Series One, Episode Six: The Right to Know): Sir Humphrey : Minister, I have something to say to you which you may not like to hear. Jim Hacker: Why should today be any different? Sir Humphrey: Minister, the traditional allocation of executive responsibil...
- Wed Oct 28, 2015 10:31 am UTC
- Forum: Mathematics
- Topic: hard geometry homework problem
- Replies: 7
- Views: 2746
Re: hard geometry homework problem
Yes, it is a tough one. And I was about to start writing some GeographicLib code before I noticed that this question is 5 years old. :) The OP mentioned Vincenty's formulae, which are commonly used for ellipsoid geodesic calculations. However, for the benefit of other readers who might find this thr...
- Tue Oct 27, 2015 6:01 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 1595: "30 Days Hath September"
- Replies: 132
- Views: 25934
Re: 1595: "30 Days Hath September"
This is the integer division thing I was talking about. I love the way it seems to make sense to begin with, with recognisable numbers like 52 and 365... but then you start getting crazy shit like 306 and 10. All division is integer division, operator % is modulus. Given integer y, m, d, calculate ...
- Fri Oct 16, 2015 6:21 am UTC
- Forum: Coding
- Topic: Coding: Fleeting Thoughts
- Replies: 9924
- Views: 1882381
Re: Coding: Fleeting Thoughts
New to OOP - quick question. [...] What is the canonical way to implement a function that is identical in a bunch of unrelated classes? And does python implement this? Just a quick note on terminology. A function that's defined inside a class is called a method. As Flumble said, if these classes al...
- Mon Oct 12, 2015 10:17 am UTC
- Forum: Coding
- Topic: Coding: Fleeting Thoughts
- Replies: 9924
- Views: 1882381
Re: Coding: Fleeting Thoughts
What phlip said. It's definitely a much better strategy these days to learn Python 3. You should start with the official Python tutorial , since it's aimed at people who already know how to program. If you want to be able to read old code &/or use old libraries properly you will eventually need ...
- Sat Oct 10, 2015 6:20 am UTC
- Forum: Mathematics
- Topic: Set of particular numbers
- Replies: 14
- Views: 2700
Re: Set of particular numbers
Are those sequences related to any other problem in number theory? Probably not. As Conman said earlier, sequences like this don't usually reveal anything particularly deep about the numbers involved because the results depend on the base you're using to represent the numbers. There's nothing of pa...
- Wed Oct 07, 2015 7:17 am UTC
- Forum: Science
- Topic: Miscellaneous Science Questions
- Replies: 2904
- Views: 676047
Re: RELATIVITY QUESTIONS! (and other common queries)
FWIW, Greg Egan created some nice diagrams, images, and a Java applet illustrating the neighbourhood of a pure GR Schwarzschild black hole to accompany his short story the Planck Dive . I guess it'd be nice to have graphics that somehow illustrated Hawking radiation, but it's not exactly easy to see...
- Mon Oct 05, 2015 6:52 am UTC
- Forum: Mathematics
- Topic: Composite numbers and polynomials
- Replies: 9
- Views: 2660
Re: Composite numbers and polynomials
If we can build a diophantine equation giving all the prime numbers even if it is not workable then why not trying to build functions or sequences or polynomials giving ONLY all the composite numbers. I started some ideas to find such way to solve this problem using some binary partition. A much si...
- Fri Oct 02, 2015 8:35 am UTC
- Forum: Fictional Science
- Topic: Superpower gives control over water - can they fly?
- Replies: 42
- Views: 12177
Re: Superpower gives control over water - can they fly?
Conservation of momentum is very native and natural to us, much moreso than conservation of energy. So in fiction, conservation of energy often goes out the window but conservation of momentum will be preserved to a degree, since things would look strange without it. I guess so. OTOH, it's because ...
- Fri Oct 02, 2015 8:21 am UTC
- Forum: Mathematics
- Topic: Composite numbers and polynomials
- Replies: 9
- Views: 2660
Re: Composite numbers and polynomials
I don't believe that it's possible to do what you want with a finite degree polynomial without overlapping: the structure of the primes is too rich for that. On a closely related note, there is the Diophantine Representation of the Set of Prime Numbers by James P. Jones, Daihachiro Sato, Hideo Wada ...
- Thu Oct 01, 2015 7:01 am UTC
- Forum: Science
- Topic: Speed of waves in water
- Replies: 8
- Views: 5373
Re: Speed of waves in water
I'm used to the concept that, say, sound waves and light waves travel at a constant speed in a constant medium, unaffected by either frequency or amplitude That's not true: wave speeds in a given medium generally are dependent on frequency / wavelength. One well-known manifestation of this is the d...
- Fri Sep 18, 2015 10:50 am UTC
- Forum: Coding
- Topic: Best password improver
- Replies: 62
- Views: 10563
Re: Best password improver
Your password page could have an embedded client-side password hasher, eg Xanthir's SHA-1 password hasher , (maybe with a slightly simplified, more user-friendly UI), with clear instructions on how to use it. And I guess you could include a brief explanation of why it's secure: it does its calculati...
- Sat Sep 12, 2015 9:25 am UTC
- Forum: Computer Science
- Topic: A formula based approach to Arithmetic Coding
- Replies: 4
- Views: 7027
Re: A formula based approach to Arithmetic Coding
siara wrote:By the way, how were you able to post URL in the reply? I couldn't.
The answer to that question can be found in the xkcd Forum Rules, along with other useful information.
- Fri Aug 28, 2015 6:57 am UTC
- Forum: Science
- Topic: A million years
- Replies: 59
- Views: 8772
Re: A million years
BlackSails wrote:Positions of planets cant be accurately predicted to more than a few tens of millions of years.
p1t1o wrote:Not necessarily, as linked above.
I suspect that you misread BlackSails's post, p1t1o.

- Tue Aug 04, 2015 5:14 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 1559: "Driving"
- Replies: 142
- Views: 20240
Re: 1559: "Driving"
If a car gets a signal to pick someone up, but is blocked by other self driving cars, it could transmit a "I need to leave now" signal to nearby cars, which would then move out of the way, then shuffle back into the available parking space. The image of a parking lot stuffed full of self-...
- Tue Aug 04, 2015 4:32 am UTC
- Forum: General
- Topic: Thoughts for ships
- Replies: 90089
- Views: 8470275
Re: Inspirations
Trying to read Ulysses [...] Kinda reminds me of Deva and addams' posts. Na-Uh! No! No Way! Deva and I are both easier to read than Ulysses is. oh, dear God! That's what you see when I post?? I should seriously consider Not posting. The world is difficult enough to understand. It is Wrong to needle...
- Mon Aug 03, 2015 7:48 am UTC
- Forum: Science
- Topic: Salty Brine State Beach explosion
- Replies: 4
- Views: 2006
Re: Salty Brine State Beach explosion
[...]Water, on the other hand, can hold quite a bit of hydrogen. (They call it hydrogen peroxide, you know.)[...] Not quite. Hydrogen peroxide is H 2 O 2 . Hydrogen peroxide is a powerful oxidizing agent and somewhat unstable due to the O-O (peroxide) bond. FWIW, when it decomposes it tends to give...
- Sat Aug 01, 2015 7:57 am UTC
- Forum: Mathematics
- Topic: Favorite math jokes
- Replies: 1452
- Views: 474547
Re: Favorite math jokes
Then you can prove that zeta(1)=infinity, without assuming that there are infinitely many primes. (though that's hard, and the usual easy proof uses the fact that there are infinitely many primes) Huh? The usual easy proof of the divergence of zeta(1) is Nicole Oresme's proof using comparison of th...
- Thu Jul 30, 2015 8:33 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 1556: "The Sky"
- Replies: 53
- Views: 13366
Re: 1556: "The Sky"
[...] the light source here (gigantic ball of explosion far older than life on this planet, not shown) [...] The Sun's not as explosion-y as you might think. The Sun's atoms certainly have a lot of kinetic energy , and sure, it has nuclear fusion reactions happening in its core, but those reactions...
- Thu Jul 30, 2015 7:39 am UTC
- Forum: The Help Desk
- Topic: What's your virus/security procedure?
- Replies: 33
- Views: 9703
Re: What's your virus/security procedure?
FWIW, I have XP on this machine for those very rare occasions when I need Windows, but since XP was discontinued I turn off my ADSL modem before booting into XP. Another useful anti-malware program that still works on XP is AdwCleaner - it can occasionally find things that MBAM misses. Obviously, I ...
- Sat Jul 25, 2015 10:51 am UTC
- Forum: Coding
- Topic: Python - Best way to turn string of digits into list of ints
- Replies: 11
- Views: 4364
Re: Python - Best way to turn string of digits into list of
I wouldn't call a 10% difference negligible, but YMMV. But do I agree that 25 microseconds is negligible. The relative speed difference of the two methods depends on the speed of the computation inside the list comp / gen exp: if that computation is slow it may dominate the total time, hiding the di...
- Fri Jul 24, 2015 12:14 pm UTC
- Forum: Mathematics
- Topic: Newtonian equation of motion for New Horizons
- Replies: 5
- Views: 2208
Re: Newtonian equation of motion for New Horizons
How about 4π² AU³/yr² ?
But what's a minor constant of proportionality between friends?
But what's a minor constant of proportionality between friends?

- Thu Jul 23, 2015 12:15 pm UTC
- Forum: Science
- Topic: N-Body Simulation questions
- Replies: 19
- Views: 3739
Re: N-Body Simulation questions
One problem with Runge–Kutta methods is that they don't conserve energy, and that could be killing your filaments. Try using a symplectic integrator like Verlet, or Leapfrog . I generally use the synchronized version of Leapfrog (for doing simple orbit sims) but the standard version's probably adequ...
- Thu Jul 23, 2015 11:49 am UTC
- Forum: Mathematics
- Topic: Newtonian equation of motion for New Horizons
- Replies: 5
- Views: 2208
Re: Newtonian equation of motion for New Horizons
A minor correction: G is normally called the gravitational constant ; the term "gravitational parameter" or standard gravitational parameter normally denotes the product GM. In celestial mechanics, the standard gravitational parameter μ of a celestial body is the product of the gravitation...
- Tue Jul 21, 2015 7:14 am UTC
- Forum: Coding
- Topic: Coding: Fleeting Thoughts
- Replies: 9924
- Views: 1882381
Re: Coding: Fleeting Thoughts
ETA: yep, it's perfect. Thanks! No worries. When you're done, it'd be great if you could let us know what you think of svg_stack. OTOH, since your SVG files are all nearly identical it probably wouldn't be too hard to write a bit of Python to do the tiling yourself, assuming that the files were bui...
- Mon Jul 20, 2015 8:43 am UTC
- Forum: Coding
- Topic: Coding: Fleeting Thoughts
- Replies: 9924
- Views: 1882381
Re: Coding: Fleeting Thoughts
I have a large amount of SVG files (all nearly identical) which I want to put on a single page in a simple rectangular tiled layout. I assume you want to tile all these files into a single SVG file, rather than into a HTML / XHTML Web page. If so, svg_stack may be helpful. svg_stack combines multip...
- Fri Jul 17, 2015 9:01 am UTC
- Forum: Coding
- Topic: Python - Best way to turn string of digits into list of ints
- Replies: 11
- Views: 4364
Re: Python - Best way to turn string of digits into list of
I wasn't aware that list comps create their own scope, now. Lots of people have been bitten by the "scope-leaking" of Python 2 list comps. Most of us just learned to live with it, but enough people complained that it was changed for Python 3, even though it makes list comps slightly less ...
- Thu Jul 16, 2015 12:20 pm UTC
- Forum: Coding
- Topic: Python - Best way to turn string of digits into list of ints
- Replies: 11
- Views: 4364
Re: Python - Best way to turn string of digits into list of
@MostlyHarmless What they said. Generators (including generator expressions) run slightly slower than list comprehension and take more setup time, so list comprehensions will beat them for stuff like this unless you're processing ridiculously huge strings of digits. BTW, in general, don't use `chr` ...
- Thu Jul 16, 2015 10:54 am UTC
- Forum: General
- Topic: Thoughts for ships
- Replies: 90089
- Views: 8470275
Re: Inspirations
You could do a Death Star cake and if someone asks which moon it is your SO can reply
"That's no moon".

"That's no moon".

- Mon Jul 13, 2015 6:42 am UTC
- Forum: Mathematics
- Topic: Wanted: Elegant proof of sin(x)/x limit
- Replies: 49
- Views: 8529
Re: Wanted: Elegant proof of sin(x)/x limit
FWIW, the Wikipedia article on the Fermat point (the point such that the total distance from the three vertices of the triangle to the point is the minimum possible) invokes without proof "the dogleg rule" which asserts that if a triangle and a polygon have one side in common and the rest ...
- Mon Jul 13, 2015 6:36 am UTC
- Forum: Science
- Topic: Problem about travelling backwards
- Replies: 15
- Views: 3233
Re: Problem about travelling backwards
As I've mentioned before, I'm rather fond of Cramer's Transactional Interpretation of quantum mechanics. Roughly speaking, Cramer postulates that the normal past-to-future causality is complemented by future-to-past causality, so when atom A emits a photon that's absorbed by atom B, the actual traje...
- Mon Jul 13, 2015 6:16 am UTC
- Forum: Science
- Topic: Conductors and Motors/Generators
- Replies: 7
- Views: 1824
Re: Conductors and Motors/Generators
Speaking of liquid conductors & motors, check out the mercury "motor" . It's not very practical, but it is rather cute. WRT Carbon: it conducts, but rather poorly. Try running an electric current through a stick of pencil lead and see what happens! True, but graphite is a great lubrica...
- Sat Jul 11, 2015 7:07 am UTC
- Forum: General
- Topic: Thoughts for ships
- Replies: 90089
- Views: 8470275
Re: Inspirations
Echo244 wrote:I think they're invasive in Australia, and a bit tricky to get rid of.
They are. Also, blackberries can harbour rabbits, another invasive species.
- Sat Jul 11, 2015 6:57 am UTC
- Forum: Mathematics
- Topic: Math: Fleeting Thoughts
- Replies: 408
- Views: 135666