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#1
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Questions about RAND() function
What kind of distribution does the RAND() function generate, e.g. uniform,
normal, discrete etc? Can it's distribution type be changed? I know how to use the "random number generation tool". |
#2
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Questions about RAND() function
PSRumbagh -
What kind of distribution does the RAND() function generate, e.g. uniform, normal, discrete etc? < Uniform, between zero and one. Can it's distribution type be changed? < No. But, if you have a function for the inverse cumulative for a specific distribution of interest, you can use RAND() to generate values from that specific distribution. For example, NORMINV is the inverse cumulative function for the normal distribution, so you can generate normal random numbers using =NORMINV(RAND(),mean,stdev). - Mike Middleton http://www.DecisionToolworks.com Decision Analysis Add-ins for Excel "PSRumbagh" wrote in message ... What kind of distribution does the RAND() function generate, e.g. uniform, normal, discrete etc? Can it's distribution type be changed? I know how to use the "random number generation tool". |
#3
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Questions about RAND() function
Check the first sentence in Excel help for RAND.
One can always generate a particular type of random variable from the fact that the CDF follows a uniform distribution. While it may not be the most efficient way to do so, it works. So, to generate a normally distributed random variable use NORMINV(RAND(),{normal distribution parameters}). Similarly, use GAMMAINV, CHIINV, etc. Use the same technique for discrete distributions, but now it might be easier to also use a few cells. For example, to generate 1, 2, and 3 with probability 0.2, 0.7, and 0.1 respectively, put 0, 0.2, and 0.9 in 3 contiguous cells in a column. Put 1, 2, and 3 in the corresponding rows in the column to the right. Then, use =VLOOKUP(RAND(),{2-column-range-from-above}, 2, TRUE) to generate the random value(s). On Wed, 19 Nov 2008 17:30:01 -0800, PSRumbagh wrote: What kind of distribution does the RAND() function generate, e.g. uniform, normal, discrete etc? Can it's distribution type be changed? I know how to use the "random number generation tool". Regards, Tushar Mehta Microsoft MVP Excel 2000-2008 www.tushar-mehta.com Tutorials and add-ins for Excel, PowerPoint, and other products |
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