PROGRAM main
      REAL tol, x, xd, tmp1, tmp1d
      INTEGER r, it

      tol = 1.0e-3
      r = 0
      x = 6
      WRITE(*, '(/, A, F3.1)') '  Initial guess: ', x
      xd = 1
      WRITE(*, '(A, F3.1)') '  Initial guess direction: ', xd
      it = 20
      WRITE(*, '(A, I4)') '  Iteration times: ', it
      WRITE(*, '(/, A)') "     x       f(x)      f'(x)"
      DO
        CALL F_D( x, xd, tmp1, tmp1d )
        WRITE(*, '(3(F9.5, X))') x, tmp1, tmp1d
C
        x = x - ( tmp1 / tmp1d ) 
        IF ( ABS( tmp1d ) < tol ) EXIT
        r = r + 1
        IF ( r > it ) EXIT
      END DO
      END 

      SUBROUTINE F( x, y ) 
      REAL x, y

      IF ( x > 1 ) THEN
         y = x**2
      ELSE
         y = 2-x**2
      ENDIF
      END