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Bessel function of second kind of order one.


double x, y, y1();
y = y1(x);


Returns a Bessel function of the second kind of order one of the argument.

The domain is divided into the intervals [0, 8] and (8, infinity). In the first interval a 25 term Chebyshev expansion is used, and a call to j1() is required. In the second, the asymptotic trigonometric representation is employed using two rational functions of degree 5/5.

                      Absolute error:
arithmetic   domain      # trials      peak         rms
    DEC       0, 30       10000       8.6e-17     1.3e-17
    IEEE      0, 30       30000       1.0e-15     1.3e-16

(error criterion relative when |y1| > 1).