REAL FUNCTION WORK1(I)
  INTEGER I
  WORK1 = 1.0 * I
  RETURN
END FUNCTION WORK1

REAL FUNCTION WORK2(I)
  INTEGER I
  WORK2 = 2.0 * I
  RETURN
END FUNCTION WORK2

SUBROUTINE atomic_example(X, Y, INDEX, N)
  REAL X(*), Y(*)
  INTEGER INDEX(*), N
  INTEGER I
!$OMP PARALLEL DO SHARED(X, Y, INDEX, N)
  DO I=1,N
    !$OMP ATOMIC UPDATE
    X(INDEX(I)) = X(INDEX(I)) + WORK1(I)
    Y(I) = Y(I) + WORK2(I)
  ENDDO
END SUBROUTINE atomic_example

PROGRAM ATOMIC_EXAMPLE
  REAL X(1000000), Y(10000000)
  INTEGER INDEX(10000000)
  INTEGER I
  DO I=1,10000000
     INDEX(I) = MOD(I, 1000000) + 1
     Y(I) = 0.0
  ENDDO
  DO I = 1,1000000
     X(I) = 0.0
  ENDDO
  CALL atomic_example(X, Y, INDEX, 10000000)

END PROGRAM ATOMIC_EXAMPLE