Special functions: Incomplete beta functions

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INCOMPLETE BETA FUNCTIONS

Like the incomplete gamma function, there are four "variations" of the outputs we can get:

1. Incomplete beta ratio lower tail
2. Incomplete beta ratio upper tail
3. Incomplete beta lower tail
4. Incomplete beta upper tail

In this blog when the nature of the function is not specified we refer to the ratio lower tail that will be the object of the Excel formulas and user defined functions presented

BETA DISTRIBUTION

             

EXCEL FORMULA AND USER DEFINED FUNCTIONS

' Incomplete beta ratio function Function xlINCBETA(x, a, b)   With WorksheetFunction     xlINCBETA = .Beta_Dist(x, a, b, 1)   End With End Function

MATLAB

>> betainc(.5,.5,.2,'lower') ans =     0.2682 >>  betainc(.5,.5,.2,'upper') ans =     0.7318