Exceptional Argument            Routine Behavior

    (y0(), y1(),  yn()) x < 0       Invalid argument
    (y0(), y1(),  yn()) x = 0       Overflow

    The j1() and jn()  functions can result in an underflow as x
    becomes small. The largest value of x for which this occurs is a
    function of n.

    The y1() and yn()  functions can result in an overflow as x
    becomes small. The largest value of x for which this occurs is
    a function of n.