[PD] Shuffling arrays
matju at artengine.ca
Mon Oct 4 17:56:51 CEST 2010
On Mon, 4 Oct 2010, martin.peach at sympatico.ca wrote:
> That's a bad way to shuffle, as it can swap things back again and
> generally reduce the randomness, the way someone who is good at shufflng
> cards can put them all back the way they started while appearing to mix
> them up.
But the programme is not meaning to swap things back. If things are
swapped back in a random fashion, where the probability of swapping back
follows from a sequence of independent uniform random-variables, what's
the problem with that ? It's like the probability of getting twice the
same dice number in a row, there's a certain amount of random repetition
that is considered normal.
How would you write a formal proof of what you say ?
But I also believe that the quickest perfectly fair shuffle is done a lot
more like [urn] than like swapping random elements. The latter converges
towards being fair eventually, whereas [urn] is fair in N steps if
random() is fair. The former doesn't take so many steps, but one has to
decide where to stop swapping, and that's not a decision I'd like to be
making, so I prefer [urn]-like processes (or similarly, [#grade]-like
| Mathieu Bouchard ------------------------------ Villeray, Montréal, QC
More information about the Pd-list