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betainv
can anybody explain what all the parameter's for the beta distribution mean
specifically i am trying to use this to create a randomly distributed number between two point's with a beta distribution |
#2
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betainv
See
http://mathworld.wolfram.com/BetaDistribution.html for the formula of the beta distribution, including the parameters alpha and beta, which control the shape of the distribution. The optional parameters A and B linearly shift the range of x from (0,1) to (A,B), so that BETADIST(x,a,b,A,B)=BETADIST((x-A)/(B-A),a,b) Theoretically, BETAINV(RAND(),a,b,A,B) is a random variable that follows the Beta(a,b) distribution spread between A and B. For serious work, I would be suspicious of RAND() in Excel versions prior to 2003, and would be suspicious of BETAINV() in all versions. If you do not have Excel 2003, I suggest using the algorithm of its new (greatly improved) random number generator http://support.microsoft.com/kb/q828795/ Ian Smith has implemented it in VBA http://groups.google.com/group/micro...rogramming/msg... An even better algorithm is the Mersenne Twister http://www.math.sci.hiroshima-u.ac.j...at/MT/emt.html http://www-personal.engin.umich.edu/...neTwister.html which is implemented in the freeware NtRand http://www.numtech.com/NtRand/ For inverse distribution functions, I would recommend Ian Smith's VBA library http://members.aol.com/iandjmsmith/Examples.xls even if you do have Excel 2003. Jerry wrote: can anybody explain what all the parameter's for the beta distribution mean specifically i am trying to use this to create a randomly distributed number between two point's with a beta distribution |
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