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 13, 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
