{{alias}}( x )
    Evaluates the natural logarithm of `1+x`.

    For `x < -1`, the function returns `NaN`, as the natural logarithm is not
    defined for negative numbers.

    Parameters
    ----------
    x: number
        Input value.

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

    Examples
    --------
    > var y = {{alias}}( 4.0 )
    ~1.609
    > y = {{alias}}( -1.0 )
    -Infinity
    > y = {{alias}}( 0.0 )
    0.0
    > y = {{alias}}( -0.0 )
    -0.0
    > y = {{alias}}( -2.0 )
    NaN
    > y = {{alias}}( NaN )
    NaN

    See Also
    --------