BEI1

This function evaluates the Kelvin function of the first kind, bei, of order one.

Function Return Value

BEI1 — Function value. (Output)

Required Arguments

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

FORTRAN 90 Interface

Generic: BEI1 (X)

Specific: The specific interface names are S_BEI1 and D_BEI1.

FORTRAN 77 Interface

Single: BEI1 (X)

Double: The double precision name is DBEI1.

Description

The Kelvin function bei1(x) is defined to be ℑJ1(xe3πi∕4). The Bessel function J1(x) is defined in BSJ1. Function BEI1 is based on the work of Burgoyne (1963).

If ∣x∣ > 119, then NaN (not a number) is returned.

Example

In this example, bei1(0.4) is computed and printed.

 

USE BEI1_INT

USE UMACH_INT

 

IMPLICIT NONE

! Declare variables

INTEGER NOUT

REAL VALUE, X

! Compute

X = 0.4

VALUE = BEI1(X)

! Print the results

CALL UMACH (2, NOUT)

WRITE (NOUT,99999) X, VALUE

99999 FORMAT (' BEI1(', F6.3, ') = ', F6.3)

END

Output

 

BEI1( 0.400) = 0.139