ber = kelvin\_ber(x) evaluates an approximation to the Kelvin function ber x.

The function is based on several Chebyshev expansions. For large x, there is a danger of the result being totally inaccurate, as the error amplification factor grows in an essentially exponential manner; therefore the function must fail.

For more information please review the s19aac function in the NAG document


x (input, double)
The argument x of the function.
ber (output, double)
Approximation of the Kelvin function ber x.