
{{alias}}( p, a[, upper] )
    Computes the inverse of the lower incomplete gamma function.

    In contrast to a more commonly used definition, the first argument is the
    probability `p` and the second argument is the scale factor `a`.

    By default, the function inverts the lower regularized incomplete gamma
    function, `P(x,a)`. To invert the upper function `Q(x,a)`, set the `upper`
    argument to `true`.

    If provided `NaN` as any argument, the function returns `NaN`.

    If provided `p < 0` or `p > 1`, the function returns `NaN`.

    Parameters
    ----------
    p: number
        Probability.

    a: number
        Scale parameter.

    upper: boolean (optional)
        Boolean indicating if the function should invert the upper tail of the
        incomplete gamma function; i.e., compute `xr` such that `Q(a,xr) = p`.
        Default: `false`.

    Returns
    -------
    y: number
        Function value.

    Examples
    --------
    > var y = {{alias}}( 0.5, 2.0 )
    ~1.678
    > y = {{alias}}( 0.1, 10.0 )
    ~6.221
    > y = {{alias}}( 0.75, 3.0 )
    ~3.92
    > y = {{alias}}( 0.75, 3.0, true )
    ~1.727
    > y = {{alias}}( 0.75, NaN )
    NaN
    > y = {{alias}}( NaN, 3.0 )
    NaN

    See Also
    --------

