Calculate the Gamma function Γ(z), the log Gamma function ln(Γ(z)), the incomplete lower Gamma function γ(z,x), the incomplete upper Gamma function Γ(z,x), the incomplete lower Gamma unit function PL(z,x), the incomplete upper Gamma unit function PU(z,x).
The Gamma function is a continuous form of the integer factorial:
`n! = Γ(n + 1) `
The Gamma function is recursive for values greater than 1 or less than 0 (z > 1 or z < 0).
`Γ(z + 1) = z Γ(z) `
The Gamma function is invalid if z equals zero, or if z is a negative integer. The lower incomplete Gamma unit functions are defined as
`PL(z,x) = γ(z,x) / Γ(z) `
`PU(z,x) = Γ(z,x) / Γ(z) `
Use the Result Plot option to plot the Gamma functions versus z.
Reference : Numerical Recipes, The Art Of Scientific Computing, Press, Teukolsky, Vetterling, Flannery, Cambridge University Press
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