def _sign(x):
    """ Return the sign of x
    INPUTS
    ------
    x: number
        value to get the sign of

    OUTPUTS
    -------
    s: signed int
        -1, 0 or 1 if negative, null or positive
    """

    if (x > 0):
        return 1
    elif (x == 0):
        return 0
    else:
        return -1