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Gamma IC Function
Math Engineering Class

Public Function GammaIC( _
      ByVal vA As Variant _
    , ByVal vX As Variant _
    ) As Variant

Calculate the complementary incomplete Gamma function.

Examples: 
    GammaIC(1.0, 1.0) = 0.367879441171442
    GammaIC(1.0, 2.0) = 0.135335283236613
    GammaIC(2.0, 1.0) = 0.735758882342885
    GammaIC(2.0, 2.0) = 0.406005849709838
    GammaIC(2.2, 1.1) = 0.82996041174649
    GammaIC(2.2, 1.1) = 1 - GammaI(2.2, 1.1)
See also: 
    Gamma Function
    GammaI Function
    GammaIT Function
    GammaILn Function
    DGAMIC Function
vA: Function returns Null if vA is Null or cannot be fixed up to a Double precision floating point number.
vX: Function returns Null if vX is Null or cannot be fixed up to a Double precision floating point number.

Evaluate the complementary incomplete Gamma function 

    GammaIC = integral from X to infinity of EXP(-T) * T^(A-1.)
GammaIC is evaluated for arbitrary real values of A and for non- negative values of X (even though DGAMIC is defined for X .LT. 0.0), except that for X = 0 and A .LE. 0.0, DGAMIC is undefined.
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.

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