Wei_Dai comments on Open Thread, August 2010-- part 2 - Less Wrong

3 Post author: NancyLebovitz 09 August 2010 11:18PM

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Comment author: Wei_Dai 29 August 2010 10:20:18PM 7 points [-]

Here's my solution. The descendants of each initial blob spawn independently of descendants of other initial blobs, so this is a sum of N independent distributions. The number of descendants of one initial blob is obviously the geometric distribution. Googling "sum of independent geometric distributions" gives Negative binomial distribution as the answer.

Comment author: RobinZ 30 August 2010 12:39:51AM 1 point [-]

Agreed - there are never more than N breeding blobs, each success increases P by one, and each failure reduces the remaining number of breeding blobs by one. Essentially, if r = N, X = P-N.

Comment author: Morendil 30 August 2010 05:35:46AM 0 points [-]

Thanks for answering several questions at once. :)

Comment author: Pavitra 29 August 2010 10:35:14PM 0 points [-]

I don't think that's right. I don't have the math to show why yet, but my current working hunch says to make explicit your assumptions about whether the initial number of blobs, and the number of generations, are continuous or discrete, because the geometric distribution may not actually be right.