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### 8.27 `BESSEL_J0` — Bessel function of the first kind of order 0

Description:
  `BESSEL_J0(X)` computes the Bessel function of the first kind of order 0 of X. This function is available under the name `BESJ0` as a GNU extension.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = BESSEL_J0(X)`
Arguments:

  X | The type shall be `REAL`, and it shall be scalar.

Return value:
  The return value is of type `REAL` and lies in the range - 0.4027... \leq Bessel (0,x) \leq 1. It has the same kind as X.
Example:

                program test_besj0
                  real(8) :: x = 0.0_8
                  x = bessel_j0(x)
                end program test_besj0

Specific names:

  Name | Argument | Return type | Standard
  `DBESJ0(X)` | `REAL(8) X` | `REAL(8)` | GNU extension