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
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