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Igamma
Incomplete gamma function.
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Loading LOADSUB ALL FROM "IGAMMA.HTS"
or LOADSUB FROM "MATHLIB.HTS"
Usage REAL A,X,Y
Y=FNIgamma(A,X)
Description
FNIgamma returns the value of the incomplete gamma function of a and x, γ(a,x). Although the incomplete gamma function is defined for all values of x, this subroutine only works with values of x > 0 or x = 0 and a > 0.
γ(a,x) is defined by the expression
 In the above expression, x must be positive or zero and a must be positive.
When x ≥ 0 and a > 0, the other forms of the incomplete gamma function present in this subroutine library, the complementary form, Γ(a,x) and Tricomi's form, γ*(a,x), are related to the incomplete gamma function by the following expressions:
  Errors
FNIgamma causes an HTBasic error if its arguments are not both of type REAL, if x < 0, or if x = 0 and a ≤ 0.
See Also
Gamma, Gamic, Gamit
(a,x)
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