BSI1E

This function evaluates the exponentially scaled modified Bessel function of the first kind of order one.

Function Return Value

BSI1E — Function value. (Output)

Required Arguments

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

FORTRAN 90 Interface

Generic: BSI1E (X)

Specific: The specific interface names are S_BSI1E and D_BSI1E.

FORTRAN 77 Interface

Single: BSI1E (X)

Double: The double precision function name is DBSI1E.

Description

Function BSI1E computes e−∣x∣ I1(x). For the definition of the Bessel function I1(x), see BSI1. The function BSI1E underflows if ∣x∣/2 underflows.

Comments

Informational Error

 

Type	Code	Description
2	1	The function underflows because the absolute value of X is too small.

Example

In this example, BSI1E(4.5) is computed and printed.

 

USE BSI1E_INT

USE UMACH_INT

 

IMPLICIT NONE

! Declare variables

INTEGER NOUT

REAL VALUE, X

! Compute

X = 4.5

VALUE = BSI1E(X)

! Print the results

CALL UMACH (2, NOUT)

WRITE (NOUT,99999) X, VALUE

99999 FORMAT (' BSI1E(', F6.3, ') = ', F6.3)

END

Output

 

BSI1E( 4.500) = 0.171