# 3.5.1.3.50 Kelvin_ker

## Definition:

$ker = kelvin\_ker(x)$ evaluates an approximation to the Kelvin function ker x. The function is based on several Chebyshev expansions. For large x, kerx is so small that it cannot be computed without underflow and the function evaluation fails.

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.
her (output, double)
Approximation of the Kelvin function ker x.