Primes and Squares

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PhiNotPi

01:44

The world's fastest drum roll is 20.13 Hz, which actually brings it into the low end of human hearing.

Image manually operating a speaker and that's basically what that guy did.

El'endia Starman

02:22

wow

2 hours later…

Nathan Merrill

04:37

this is interesting: If you have a psuedo-random generator, and you want to shuffle a deck of cards, you need a rather large seed:

there are 52! ways to shuffle a deck, which means that you need to have a minumum of log2(52!) =226 bits in your seed

even a long long in C++ is only 64 bits.

5 hours later…

flawr

09:23

@NathanMerrill wow!

5 hours later…

El'endia Starman

13:59

@NathanMerrill: So, in other words, without resorting to bignum libraries, it's impossible to have a chance at randomly getting any possible shuffle of a deck of cards.

flawr

14:12

Doesn't that also depend on the period of the RNG used? I mean in theory the seed could be in a range that is a lot smaller than the period of an RNG (however I don't actually know much about RNGs)

PhiNotPi

@flawr I think generally seed size = period length

If anything, period would be smaller than the seed (but that's considered somewhat broken for a PRNG)

flawr

The Ultimate LEGO Machine Returns!

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El'endia Starman

14:30

@flawr That was great.

Nathan Merrill

14:48

@flawr I've only looked into Java's random library, but as far as I can tell, the seed is the only state saved on each random call.

flawr

15:13

It does indeed make most sense that way

1 hour later…

El'endia Starman

16:43

@orlp: physics.stackexchange.com/questions/335568/…

^ And for anyone else who was interested in the magnets-on-spinners problem.

PhiNotPi

@El'endiaStarman One thing I would point out is that inverse cube law is for dipoles (as opposed to inverse square which is monopoles).

If I were to model the problem, what I would do would to be transform it to a traditional "2D particle motion on a potential field" thing.

As for how it's 2D, one axis is angle of spinner 1 and another axis is angle of spinner 2.

El'endia Starman

@PhiNotPi Is that consistent with what was shown in the video?

The magnets are perpendicular to the plane of the spinners.

PhiNotPi

The particle is the single point that represents the current configuration. Each point on that 2D square (which wraps around the edges) has an associated potential energy value.

@El'endiaStarman It's 3D physics but 2 degrees of freedom and therefore a 2D problem (looking at configuration space).

El'endia Starman

17:50

@PhiNotPi: Embarrassingly, my real problem was that I updated the angular position of the left spinner before calculating the torque for the right spinner. Fixed version: jsfiddle.net/adq75r56/3