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[ns] Re: ParetoII
I've done a bit more investigation and have some more questions --
The ParetoII distribution is not the Lomax distribution (as defined in
"Continuous Univariate Distributions, vol. I" by Norman Johnson and Samuel
Kotz).
The sampling method for the Lomax distribution is
x = (scale / uniform())^(1/shape) - C
The sampling method for ParetoII (as used in ns-2) is
x = scale * (1 / uniform()^(1/shape) - 1)
= (scale / uniform()^(1/shape)) - scale
Interestingly, the sampling method for Pareto is
x = scale / uniform()^(1/shape)
So, ParetoII just subtracts scale from each sample generated by Pareto.
Why?
Also, the scale value is different in Pareto and ParetoII. Using the
distribution functions in ns-2, we can specify average and shape. Then scale
is computed and is used to generate samples.
For Pareto, scale = average (shape - 1) / shape
For ParetoII, scale = average (shape - 1)
Is there a reference for what ParetoII actually is and why it's used in the
webtraf simulations rather than Pareto?
Thanks,
Michele
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Michele Clark Weigle clark@cs.unc.edu
Department of Computer Science http://www.cs.unc.edu/~clark
University of North Carolina Sitterson #327
Chapel Hill, NC 27599-3175 (919) 962-1909
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