In Excel 2010, the Gammainv function has been replaced by the Gamma.Inv function, which has improved accuracy.
The Excel Gammainv function returns the inverse of the Gamma Cumulative Distribution.
The syntax of the function is:
where the function arguments are:
|probability||-||The probability value for which you want to evaluate the inverse Gamma Cumulative Distribution Function (must be between 0 & 1).|
|alpha||-||A parameter of the distribution.|
|beta||-||beta=0, then this specifies the Standard Gamma Distribution).(Note: if|
The charts below show the Gamma Cumulative Distribution and the Inverse Gamma Cumulative Distribution, with the parameter alpha set to 3 and the parameter beta set to 2.
Gamma Cumulative Distribution Function with α=3 & β=2
Inverse Gamma Cumulative Distribution with α=3 & β=2
This gives the result 5.348120627.
For further examples of the Excel Gammainv function, see the Microsoft Office website.
If you get an error from the Excel Gammainv function this is likely to be one of the following:
|#N/A||-||Occurs if Excel fails to converge to a solution after 100 iterations. Excel is unable to calculate the solution.|
|#VALUE!||-||Occurs if any of the supplied arguments is non-numeric.|