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GammaRelatedGammaIC(Double, Double) Method

Evaluate the complementary incomplete Gamma function. GammaIC(x,a) = integral from x to infinity of exp(-t) * t**(a-1) GammaIC(x,a) is evaluated for arbitrary real values of A and for non-negative values of x (even though GammaIC is defined for x < 0.0), except that for x = 0 and a <= 0.0, GammaIC is undefined.

Namespace: Altaxo.Calc
Assembly: AltaxoCore (in AltaxoCore.dll) Version: 4.8.3572.0 (4.8.3572.0)
Syntax
C#
Copy
public static double GammaIC(
	double x,
	double a
)

Parameters

x  Double
The function argument.
a  Double
The shape parameter of the incomplete gamma function.

Return Value

Double
Complementary incomplete Gamma function of arguments x and a.
Remarks
A slight deterioration of 2 or 3 digits accuracy will occur when GammaIC is very large or very small in absolute value, because log- arithmic variables are used. Also, if the parameter A is very close to a negative integer (but not a negative integer), there is a loss of accuracy, which is reported if the result is less than half machine precision. This is a translation from the Fortran version of DGAMIC, SLATEC, FNLIB, CATEGORY C7E, REVISION 920528, originally written by Fullerton W.,(LANL) to C++. References: (1) W. Gautschi, A computational procedure for incomplete gamma functions, ACM Transactions on Mathematical Software 5, 4 (December 1979), pp. 466-481. (2) W. Gautschi, Incomplete gamma functions, Algorithm 542, ACM Transactions on Mathematical Software 5, 4 (December 1979), pp. 482-489. Routines called: d9gmit, d9gmic, d9lgic, d9lgit, LnGamma(x), LnGamma(x,a)
See Also