Spherical functions computational algorithm

The spherical Bessel functions are computed by downward recursion. This recursion begins with two successive functions of small values and produces functions proportional to the Bessel functions rather than the actual Bessel functions. The constant of proportionality between the two sets of functions is obtained from the function of order zero o- Alternatively, the spherical Bessel functions can be computed with an algorithm involving the auxiliary function Xn [169]... 

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