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Looking for fortran subroutine for I Bessel function with negative order

  1. Oct 29, 2011 #1
    Hello all, I am developing a new analytical solution for a problem in flow in porous media, and I need to write it in Fortran.

    This solution contains the modified Bessel function of the first kind, I_n(x).

    The order n is a real number, and it can be both negative and positive.
    The argument x is real, and is always positive. Correct me if I'm wrong, but I believe this means I will never encounter a complex result.

    I have looked in netlib, Numerical Recipes books, and an assortment of personal webpages (Alan Miller, JP Moreau), and I still can't find a Bessel_I subroutine that will compute for negative non-integer n. Obviously they all do a splendid job for positive n.

    Alternatively, (and I have looked in functions.wolfram.com website) are you aware how I can compute this from other functions ? Gamma func ?

  2. jcsd
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