Pdf of weighted uniform random variables

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SUMMARY

The discussion focuses on deriving the probability density function (pdf) of weighted uniform random variables defined as y(i) = x(i)/(x(1)+...+x(N)), where x(1),...,x(N) are independent uniformly distributed variables on (0,1). Participants emphasize the importance of starting with the cumulative distribution function (CDF) and mention the complexity of the joint distribution of y(i). For large N, the Central Limit Theorem can be applied for approximation, while precise calculations require standard tools for sum/ratio distributions.

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  • Understanding of uniform distribution, specifically U(0,1)
  • Knowledge of cumulative distribution functions (CDF)
  • Familiarity with the Central Limit Theorem
  • Experience with sum and ratio distribution calculations
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PAHV
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Let x(1),...,x(N) all be independent uniformally distributed variables defined on (0,1), i.e. (x(1),...,x(N)) - U(0,1). Define the random variable y(i) = x(i)/(x(1)+...+x(N)) for all i=1,...,N. I’m looking for the pdf of the random variables y(1),…,y(N). Has anyone come across such random variables? If so, any references would be appreciated!
 
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I don't think it's too hard to work out. Start with deriving the CDF. P[Yi < y] = P[x(i)/(x(1)+...+x(N)) < y] = etc.
 
Is the question about the joint distribution of the y_i?
 
Yes, the question is about the joint distribution of the y(i). Any help on getting started with the pdf is highly appreciated!
 
Try doing it for n=2. Even that is quite tricky. In general it looks very messy.
 
Hey PAHV and welcome to the forums.

If N is large enough, then you can approximate the sum by using the Central Limit Theorem (i.e. normal) approximation.

If not (or you are particular on having everything precise), then use the standard tools for calculating sum/ratio distributions.
 

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