WorksheetFunction.GammaDist Method

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Excel Developer Reference

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

expression.GammaDist(Arg1, Arg2, Arg3, Arg4)

expression   A variable that represents a WorksheetFunction object.

Parameters

Name Required/Optional Data Type Description
Arg1 Required Double X - the value at which you want to evaluate the distribution.
Arg2 Required Double Alpha - a parameter to the distribution.
Arg3 Required Double Beta - a parameter to the distribution. If beta = 1, GAMMADIST returns the standard gamma distribution.
Arg4 Required Boolean Cumulative - a logical value that determines the form of the function. If cumulative is TRUE, GAMMADIST returns the cumulative distribution function; if FALSE, it returns the probability density function.

Return Value
Double

Remarks

  • 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.

  • The equation for the gamma probability density function is:

    Equation

    The standard gamma probability density function is:

    Equation

  • When alpha = 1, GAMMADIST returns the exponential distribution with:

    Equation

  • 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.

See Also