PROGRAM main
      REAL tol, x, xd, tmp1, tmp1d
      INTEGER r, it
      INTEGER tmp2, tmp3
      COMMON /validity_test_common/ gmin, gmax, infmin, infmax
      REAL gmin, gmax
      LOGICAL infmin, infmax

      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)     gmin      gmax
     +    infmin infmax"
     gmin=.0
     gmax=.0
     infmin=.TRUE.
     infmax=.TRUE.
      DO
        CALL F_DVA(x, xd, tmp1, tmp1d)
        IF ( infmin .eqv. .TRUE. ) THEN 
          tmp2 = 1 
        ELSE 
          tmp2 = 0 
        END IF
        IF ( infmax .eqv. .TRUE. ) THEN 
          tmp3 = 1 
        ELSE 
          tmp3 = 0 
        END IF
        WRITE(*, '(5(F9.5, X), I5, X, I5)') x, tmp1, tmp1d, gmin, gmax 
     +   , tmp2, tmp3
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