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Bessel function of integer order.


int n;
double x, y, jn();
y = jn(n, x);


Returns a Bessel function of order n, where n is a (possibly negative) integer.
The ratio of jn(x) to j0(x) is computed by backward recurrence.  First the ratio jn/jn-1 is found by a continued fraction expansion. Then the recurrence relating successive orders is applied until j0 or j1 is reached.
If n = 0 or 1 the routine for j0 or j1 is called directly.

                      Absolute error:
arithmetic   range      # trials      peak         rms
    DEC       0, 30        5500       6.9e-17     9.3e-18
    IEEE      0, 30        5000       4.4e-16     7.9e-17

Not suitable for large n or x. Use jv() instead.