kelvin_berreturns a value for the Kelvin function .
For full information please refer to the NAG Library document for s19aa
The argument of the function.
The value of the function at .
- (errno )
On entry, .
is too large for an accurate result to be returned and the function returns zero.
kelvin_berevaluates an approximation to the Kelvin function .
Note: , so the approximation need only consider .
The function is based on several Chebyshev expansions:
where , ,
and , , , and are expansions in the variable .
When is sufficiently close to zero, the result is set directly to .
For large , 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.
NIST Digital Library of Mathematical Functions