Evaluates the real gamma function.

x—Point at which the gamma function is to be evaluated.

result—The value of the gamma function Γ(x).

Double—If present and nonzero, double precision is used.

The gamma function, Γ(x), is defined to be:

For x < 0, the above definition is extended by analytic continuation.

The gamma function is not defined for integers less than or equal to zero. It underflows for x << 0 and overflows for large x. It also overflows for values near negative integers.

In this example, Γ(1.5) is computed and printed.

x  =  1.5

ans  =  GAMMA_ADV(x)

PRINT, 'Gamma(', x, ') =', ans

; PV-WAVE prints: Gamma( 1.50000) = 0.886227

STAT_SMALL_ARG_UNDERFLOW—The parameter x must be large enough that Γ(x) does not underflow. The underflow limit occurs first for parameters close to large negative half integers. Even though other parameters away from these half integers may yield machine-representable values of Γ(x), such parameters are considered illegal.

STAT_NEARR_NEG_INT_WARN—The result is accurate to less than one-half precision because x is too close to a negative integer.

STAT_ZERO_ARG_OVERFLOW—The parameter for the gamma function is too close to zero.

STAT_NEAR_NEG_INT_FATAL—The parameter for the function is too close to a negative integer.

STAT_LARGE_ARG_OVERFLOW—The function overflows because x is too large.

STAT_CANNOT_FIND_XMIN—The algorithm used to find xmin failed. This error should never occur.

STAT_CANNOT_FIND_XMAX—The algorithm used to find xmax failed. This error should never occur.