# Kelvin_ber

Kelvin-ber-func

## Definition:

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

## Parameters:

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