..
  Copyright 1988-2021 Free Software Foundation, Inc.
  This is part of the GCC manual.
  For copying conditions, see the GPL license file

.. _bessel_j1:

BESSEL_J1 --- Bessel function of the first kind of order 1
**********************************************************

.. index:: BESSEL_J1

.. index:: BESJ1

.. index:: DBESJ1

.. index:: Bessel function, first kind

.. function:: BESSEL_J1(X)

  ``BESSEL_J1(X)`` computes the Bessel function of the first kind of
  order 1 of :samp:`{X}`. This function is available under the name
  ``BESJ1`` as a GNU extension.

  :param X:
    The type shall be ``REAL``.

  :return:
    The return value is of type ``REAL`` and lies in the
    range - 0.5818... \leq Bessel (0,x) \leq 0.5818 . It has the same
    kind as :samp:`{X}`.

  :samp:`{Standard}:`
    Fortran 2008

  :samp:`{Class}:`
    Elemental function

  :samp:`{Syntax}:`

  .. code-block:: fortran

    RESULT = BESSEL_J1(X)

  :samp:`{Example}:`

    .. code-block:: fortran

      program test_besj1
        real(8) :: x = 1.0_8
        x = bessel_j1(x)
      end program test_besj1

  :samp:`{Specific names}:`
    =============  =============  ===========  =============
    Name           Argument       Return type  Standard
    =============  =============  ===========  =============
    ``DBESJ1(X)``  ``REAL(8) X``  ``REAL(8)``  GNU extension
    =============  =============  ===========  =============