GAMMADIST ( x , alpha , beta , cumulative-flag )
Description: Computes the gamma distribution.
Mathematical Formula:
The equation for the gamma probability density function is:
The standard gamma probability density function is:
When alpha = 1, GAMMADIST returns the exponential distribution with:
For a positive integer n, when alpha = n/2, beta = 2, and cumulative = TRUE, GAMMADIST returns (1-CHIDIST(x)) with n degrees of freedom.
When alpha is a positive integer, GAMMADIST is also known as the Erlang distribution.
Arguments:
|
Name |
Type |
Description |
|
number |
The value at which the distribution is to be evaluated. | |
|
alpha |
number |
A parameter of the distribution. |
|
beta |
number |
A parameter of the distribution. If beta = 1, GAMMADIST returns the standard gamma distribution. |
|
cumulative-flag |
logical |
Determines the form of the function. If TRUE, GAMMADIST returns the cumulative distribution function; if FALSE, it returns the probability density function. |
Return Type and Value: number – The gamma distribution.
However, if
• x < 0, #NUM! is returned.
• alpha ≤ 0 or beta ≤ 0, #NUM! is returned.
[Example:
GAMMADIST(10,9,2,FALSE) results in 0.03263902
GAMMADIST(10,9,2,TRUE) results in 0.068093631
end example]