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9.42 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