BSI0

This function evaluates the modified Bessel function of the first kind of order zero.

Function Return Value

BSI0 — Function value. (Output)

Required Arguments

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

FORTRAN 90 Interface

Generic: BSI0 (X)

Specific: The specific interface names are S_BSI0 and D_BSI0.

FORTRAN 77 Interface

Single: BSI0 (X)

Double: The double precision function name is DBSI0.

Description

The Bessel function I0(x) is defined to be

 

The absolute value of the argument x must not be so large that e∣x∣ overflows.

 

Figure 1,  Plot of I0(x) and I1(x)

Example

In this example, I0 (4.5) is computed and printed.

 

USE BSI0_INT

USE UMACH_INT

 

IMPLICIT NONE

! Declare variables

INTEGER NOUT

REAL VALUE, X

! Compute

X = 4.5

VALUE = BSI0(X)

! Print the results

CALL UMACH (2, NOUT)

WRITE (NOUT,99999) X, VALUE

99999 FORMAT (' BSI0(', F6.3, ') = ', F6.3)

END

Output

 

BSI0( 4.500) = 17.481