GAMMA_ADV Function
Evaluates the real gamma function.
Usage
result = GAMMA_ADV(x)
Input Parameters
x—Point at which the gamma function is to be evaluated.
Returned Value
result—The value of the gamma function Γ(x).
Input Keywords
Double—If present and nonzero, double precision is used.
Discussion
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.
Example
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
Alert Errors
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.
Warning Errors
STAT_NEARR_NEG_INT_WARN—The result is accurate to less than one-half precision because x is too close to a negative integer.
Fatal Errors
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.
