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kn

Modified Bessel function, third kind, integer order.

SYNOPSIS:

double x, y, kn();
int n;
y = kn(n, x);

DESCRIPTION:

Returns the modified Bessel function of the third kind, of order n of the argument.

The range is partitioned into the two intervals [0,9.55] and (9.55, infinity). An ascending power series is used in the low range, and an asymptotic expansion in the high range.

ACCURACY:
Relative error:
arithmetic domain # trials peak rms
DEC 0,30 3000 1.3e-9 5.8e-11
IEEE 0,30 90000 1.8e-8 3.0e-10

Error is high only near the crossover point x = 9.55 between the two expansions used.