Lahey/GNU Fortran

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8.28 BESSEL_JN — Bessel function of the first kind

Description:
BESSEL_JN(N, X) computes the Bessel function of the first kind of order N of X. This function is available under the name BESJN as a GNU extension. If N and X are arrays, their ranks and shapes shall conform.

BESSEL_JN(N1, N2, X) returns an array with the Bessel functions of the first kind of the orders N1 to N2.

Standard:
Fortran 2008 and later, negative N is allowed as GNU extension
Class:
Elemental function, except for the transformational function BESSEL_JN(N1, N2, X)
Syntax:

RESULT = BESSEL_JN(N, X)
RESULT = BESSEL_JN(N1, N2, X)

Arguments:

N Shall be a scalar or an array of type INTEGER.
N1 Shall be a non-negative scalar of type INTEGER.
N2 Shall be a non-negative scalar of type INTEGER.
X Shall be a scalar or an array of type REAL; for BESSEL_JN(N1, N2, X) it shall be scalar.

Return value:
The return value is a scalar of type REAL. It has the same kind as X.
Note:
The transformational function uses a recurrence algorithm which might, for some values of X, lead to different results than calls to the elemental function.
Example:
          program test_besjn
            real(8) :: x = 1.0_8
            x = bessel_jn(5,x)
          end program test_besjn
     

Specific names:

Name Argument Return type Standard
DBESJN(N, X) INTEGER N REAL(8) GNU extension
REAL(8) X