# 3.5.1.3.15 Bessel_k0

## Definition:

$k0 = bessel\_k0(x)$ evaluates an approximation to the modified Bessel function of the second kind,$K_0\left( x\right)$. The function is based on Chebyshev expansions.

For more information please review the s18acc function in the NAG document.

## Parameters:

x (input, double)
The argument x of the function. Constraint: x> 0.0.
k0 (output, double)
Approximation of the modified Bessel function of the second kind.