Excel Function GAMMAINV

GAMMAINV(probability, alpha, beta)

Returns the probability of getting greater than a particular value in a gamma distribution.

probability	The probability associated with the gamma distribution.
alpha	The first parameter to the distribution.
beta	The second parameter to the distribution.

Remarks

* GAMMA.INV was added in Excel 2010 to replace this function.
* The gamma distribution is a continuous distribution.
* If "probability" < 0, then #NUM! is returned.
* If "probability" > 1, then #NUM! is returned.
* If "probability" is not numeric, then #VALUE! is returned.
* If "alpha" = 0, then #NUM! is returned.
* If "alpha" is not numeric, then #VALUE! is returned.
* If "beta" = 0, then #NUM! is returned.
* If "beta" = 1, then the standard gamma distribution is used ??
* If "beta" = 0, then #NUM! is returned.
* If "beta" is not numeric, then #VALUE! is returned.
* This function uses an iterative technique for calculating the function.
* This function iterates until the result is accurate to within ±3x10^-7.
* If this function does not converge after 100 iterations, then #N/A is returned.
* In Excel 2010 the accuracy of this function was improved.
* For the Microsoft documentation refer to support.microsoft.com

	A
1	=GAMMAINV(0.068094,9,2) = 10.00
2	=GAMMAINV(0.5,4,2) = 7.34
3	=GAMMAINV(0.068,4,2) = 3.04
4	=GAMMAINV(GAMMADIST(7,5,1,TRUE),5,1) = 7.00
5	=GAMMAINV(GAMMADIST(0.5,4,2,TRUE),4,2) = 0.50
6	=GAMMAINV(0.5,4,2) = 7.34
7	=GAMMAINV(0.5,-9,2) = #NUM!
8	=GAMMAINV(-2,9,2) = #NUM!
9	=GAMMAINV(-2,"some text",2) = #VALUE!