BSIES
Evaluates a sequence of exponentially scaled modified Bessel functions of the first kind with nonnegative real order and real positive arguments.
Required Arguments
XNU — Real argument which is the lowest order desired. (Input)
It must be at least zero and less than one.
X — Real positive argument for which the sequence of Bessel functions is to be evaluated. (Input)
It must be nonnegative.
N — Number of elements in the sequence. (Input)
BSI — Vector of length N containing the values of the function through the series. (Output)
BSI(I) contains the value of the Bessel function of order I  1 + XNU at x for I = 1 to N multiplied by exp(–X).
FORTRAN 90 Interface
Generic: CALL BSIES (XNU, X, N, BSI)
Specific: The specific interface names are S_BSIES and D_BSIES.
FORTRAN 77 Interface
Single: CALL BSIES (XNU, X, N, BSI)
Double: The double precision name is DBSIES.
Description
Function BSIES evaluates , for k = 1, n. For the definition of Iv(x), see BSIS. The algorithm is based on a code due to Cody (1983), which uses backward recursion.
Example
In this example, Iv1(10.0), v = 1, , 10 is computed and printed.
 
USE BSIES_INT
USE UMACH_INT
 
IMPLICIT NONE
! Declare variables
INTEGER N
PARAMETER (N=10)
!
INTEGER K, NOUT
REAL BSI(N), X, XNU
! Compute
XNU = 0.0
X = 10.0
CALL BSIES (XNU, X, N, BSI)
! Print the results
CALL UMACH (2, NOUT)
DO 10 K=1, N
WRITE (NOUT,99999) X, XNU+K-1, X, BSI(K)
10 CONTINUE
99999 FORMAT (' exp(-', F6.3, ') * I sub ', F6.3, &
' (', F6.3, ') = ', F6.3)
END
Output
 
exp(-10.000) * I sub 0.000 (10.000) = 0.128
exp(-10.000) * I sub 1.000 (10.000) = 0.121
exp(-10.000) * I sub 2.000 (10.000) = 0.104
exp(-10.000) * I sub 3.000 (10.000) = 0.080
exp(-10.000) * I sub 4.000 (10.000) = 0.056
exp(-10.000) * I sub 5.000 (10.000) = 0.035
exp(-10.000) * I sub 6.000 (10.000) = 0.020
exp(-10.000) * I sub 7.000 (10.000) = 0.011
exp(-10.000) * I sub 8.000 (10.000) = 0.005
exp(-10.000) * I sub 9.000 (10.000) = 0.002
Published date: 03/19/2020
Last modified date: 03/19/2020