bessel_y1_real returns the value of the Bessel function .

For full information please refer to the NAG Library document for s17ad


The argument of the function.


The value of the Bessel function .

(errno )

On entry, .

Constraint: .

is too large, the function returns the amplitude of the oscillation, .

(errno )

On entry, .

Constraint: .

is undefined, the function returns zero.

(errno )

is too close to zero and there is danger of overflow, .

Constraint: .

The function returns the value of at the smallest valid argument.


bessel_y1_real evaluates an approximation to the Bessel function of the second kind .

Note: is undefined for and the function will fail for such arguments.

The function is based on four Chebyshev expansions:

For ,

For ,

where ,

and , with .

For near zero, . This approximation is used when is sufficiently small for the result to be correct to machine precision. For extremely small , there is a danger of overflow in calculating and for such arguments the function will fail.

For very large , it becomes impossible to provide results with any reasonable accuracy (see Accuracy), hence the function fails. Such arguments contain insufficient information to determine the phase of oscillation of ; only the amplitude, , can be determined and this is returned on failure. The range for which this occurs is roughly related to machine precision; the function will fail if .


NIST Digital Library of Mathematical Functions

Clenshaw, C W, 1962, Chebyshev Series for Mathematical Functions, Mathematical tables, HMSO