log-gamma ( x -- value )

Vocabulary

picomath

Inputs

x

an object

Outputs

value

an object

Definition

USING: kernel math math.functions picomath.private sequences ;

IN: picomath

:: log-gamma ( x -- value )
    x 0 <= [ "Invalid input" throw ] when x 12 <
    [ x gamma abs log ] [
        1.0 x x * / :> z 7 c nth 7 <iota> reverse
        [ [ z * ] [ c nth ] bi* + ] each x / :> series x 0.5 -
        x log * x - halfLogTwoPi + series +
    ] if ;