Compatibility - GAMMADIST Function

The GAMMADIST function replaces the GAMMA.DIST function in Excel 2010.

Description

The function returns the gamma distribution. You can use this function to study variables that may have a skewed distribution. The gamma distribution is commonly used in queuing analysis.

Syntax

GAMMADIST(x,alpha,beta,cumulative)

Arguments

Argument	Description	Required/ Optional
X	The value at which you want to evaluate the distribution.	Required
Alpha	A parameter to the distribution.	Required
Beta	A parameter to the distribution. If beta = 1, GAMMADIST returns the standard gamma distribution.	Required
Cumulative	A logical value that determines the form of the function. If cumulative is TRUE, GAMMADIST returns the cumulative distribution function. If cumulative is FALSE, GAMMADIST returns the probability density function.	Required

Notes

The equation for the gamma probability density function is −

$$f(x;\alpha ,\beta ) = \frac{1}{\beta^\alpha \Gamma (\alpha ) }x^{\alpha-1}e^{-\frac{n}{\beta}}$$
The standard gamma probability density function is −

$$f(x;\alpha ) = \frac{x^{\alpha-1}e^{-n}}{\Gamma (\alpha)}$$
When alpha = 1, GAMMADIST returns the exponential distribution with:

$$\lambda = \frac{1}{\beta}$$
For a positive integer n, when alpha = n/2, beta = 2, and cumulative = TRUE, GAMMADIST returns (1 - CHIDIST(x)) with n degrees of freedom
If x, alpha, or beta is nonnumeric, GAMMADIST returns the #VALUE! error value.
If x < 0, GAMMADIST returns the #NUM! error value.
If alpha ≤ 0 or if beta ≤ 0, GAMMADIST returns the #NUM! error value.
When alpha is a positive integer, GAMMADIST is also known as the Erlang distribution.

Example

advanced_excel_compatibility_functions.htm