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.

Nodes of different colours represent the following:

Solid arrows point from a procedure to one which it calls. Dashed
arrows point from an interface to procedures which implement that interface.
This could include the module procedures in a generic interface or the
implementation in a submodule of an interface in a parent module.

Nodes of different colours represent the following:

Solid arrows point from a procedure to one which it calls. Dashed
arrows point from an interface to procedures which implement that interface.
This could include the module procedures in a generic interface or the
implementation in a submodule of an interface in a parent module.