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

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