Intel® Fortran Compiler 17.0 Developer Guide and Reference
Elemental and Transformational Intrinsic Functions (Generic): Compute Bessel functions of the first kind.
Elemental function: result = BESSEL_JN (n, x)
Transformational function: result = BESSEL_JN (n1, n2, x)
n, n1, n2 |
(Input) Must be of type integer and nonnegative. |
x |
(Input) Must be of type real. |
The result type and kind is the same as x.
The result of BESSEL_JN (n, x) is scalar. The result value of BESSEL_JN (n , x) is a processor-dependent approximation to the Bessel function of the first kind and order n of x.
The result of BESSEL_JN (n1, n2, x) is a rank-one array with extent MAX (n2 - n1 + 1, 0). Element i of the result value of BESSEL_JN (n1, n2, x) is a processor-dependent approximation to the Bessel function of the first kind and order n1 + i - 1 of x.
BESSEL_JN (2, 1.0) has the approximate value 0.115.
Consider the following program Bessel.90:
real :: z (6) = [0:5]/5. ! 0.0 through 1.0 by 0.2
print *, z
print *, bessel_jn (2, 1.0) ! scalar argument, answer about 0.115
print *, bessel_jn (1, z) ! elemental
print *, bessel_jn (1, 4, 1.0) ! orders 1 thru 4 on a scalar
end
Compile bessel.f90 and execute the result:
> ifort Bessel.f90 -o Bessel > bessel
The above commands produce the following result:
0.0000000E+00 0.2000000 0.4000000 0.6000000 0.8000000 1.000000 0.1149035 0.0000000E+00 9.9500835E-02 0.1960266 0.2867010 0.3688421 0.4400506 0.4400506 0.1149035 1.9563355E-02 2.4766389E-03