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Modified Bessel function of order zero.


double x, y, i0();
y = i0(x);


Returns a modified Bessel function of order zero of the argument.

The function is defined as i0(x) = j0(ix).

The range is partitioned into the two intervals [0,8] and (8, infinity).  Chebyshev polynomial expansions are employed in each interval.

                      Relative error:
arithmetic   domain     # trials      peak         rms
    DEC       0,30         6000       8.2e-17     1.9e-17
    IEEE      0,30        30000       5.8e-16     1.4e-16