This function calculates the first kind Bessel function of integer order N, for any REAL X. We use here the classical recursion formula, when X > N. For X < N, Miller's algorithm is used to avoid overflows. Reference: C.W.Clenshaw, Chebyshev Series for Mathematical Functions, Mathematical Tables, Vol. 5, 1962.

Type | Intent | Optional | Attributes | Name | ||
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integer, | intent(in) | :: | N |
Order of Bessel function. |
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double precision, | intent(in) | :: | X |
Argument of the Bessel function. |