GAMMAINV

GAMMAINV(probability, alpha, beta)

Returns the inverse of the probability distribution for 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.
* This function is only available for backwards compatibility and should not be used.
* 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.
* You can use the GAMMA.DIST function to return the probability function OR the cumulative probability function for a gamma distribution.
* You can use the GAMMA function to return the gamma function value.
* You can use the PLINK{Excel,3,GAMMALN.PRECISE,Functions/GAMMALN-PRECISE-Function] function to return the natural logarithm of the gamma function.
* 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!