# Kelvin_kei

Kelvin-kei-func

## Definition:

evaluates an approximation to the Kelvin function kei x. The function is based on several Chebyshev expansions. For large x, kei x is so small that it cannot be computed without underflow and the function fails.

For more information please review the s19adc function in the NAG document.

## Parameters:

- x (input, double)
- The argument x of the function.
- Constraint: x ≥ 0.
- kei (output, double)
- Approximation of the Kelvin function kei x.