BSK1

This function evaluates the modified Bessel function of the second kind of order one.

Function Return Value

BSK1 — Function value. (Output)

Required Arguments

X — Argument for which the function value is desired. (Input)

FORTRAN 90 Interface

Generic: BSK1 (X)

Specific: The specific interface names are S_BSK1 and D_BSK1.

FORTRAN 77 Interface

Single: BSK1 (X)

Double: The double precision function name is DBSK1.

Description

The Bessel function K1(x) is defined to be

 

The argument x must be large enough (> max(1/b, s)) that K1(x) does not overflow, and x must be small enough that the approximate answer,

 

does not underflow. Here, s is the smallest representable positive floating‑point number, s = AMACH(1) , and b = AMACH(2) is the largest representable floating‑point number.

Comments

Informational Error

 

Type	Code	Description
2	1	The function underflows because X is too large.

Example

In this example, K1(0.5) is computed and printed.

 

USE BSK1_INT

USE UMACH_INT

 

IMPLICIT NONE

! Declare variables

INTEGER NOUT

REAL VALUE, X

! Compute

X = 0.5

VALUE = BSK1(X)

! Print the results

CALL UMACH (2, NOUT)

WRITE (NOUT,99999) X, VALUE

99999 FORMAT (' BSK1(', F6.3, ') = ', F6.3)

END

Output

 

BSK1( 0.500) = 1.656