BSI1
This function evaluates the modified Bessel function of the first kind of order one.
Function Return Value
BSI1 — Function value. (Output)
Required Arguments
X — Argument for which the function value is desired. (Input)
FORTRAN 90 Interface
Generic: BSI1 (X)
Specific: The specific interface names are S_BSI1 and D_BSI1.
FORTRAN 77 Interface
Single: BSI1 (X)
Double: The double precision function name is DBSI1.
Description
The Bessel function I1(x) is defined to be
The argument should not be so close to zero that I1(x) ≈ x/2 underflows, nor so large in absolute value that e∣x∣ and, therefore, I1(x) overflows.
Comments
Informational Error
Type | Code | Description |
|---|
2 | 1 | The function underflows because the absolute value of X is too small. |
Example
In this example, I1(4.5) is computed and printed.
USE BSI1_INT
USE UMACH_INT
IMPLICIT NONE
! Declare variables
INTEGER NOUT
REAL VALUE, X
! Compute
X = 4.5
VALUE = BSI1(X)
! Print the results
CALL UMACH (2, NOUT)
WRITE (NOUT,99999) X, VALUE
99999 FORMAT (' BSI1(', F6.3, ') = ', F6.3)
END
Output
BSI1( 4.500) = 15.389
