program newt1
c
      integer out
      real x
      common /inout/ out
c
      out = 6
      write(out,*) ' newton-s method'
      x = 2
      call newton(x)
      write(out, 102) x
      stop
102   format(/' the square root of 2 is ', f8.5)
      end
      subroutine func(x, fx, dfx)
c
c -- the square root of 2
c
      real x, fx, dfx
c
      fx = x * x - 2
      dfx = 2 * x
      return
      end
      subroutine newton(x)
c
c -- the solution of f(x) = 0 by newton-s method
c
      integer out
      real x, fx, dfx, x1, dx, tol
      common /inout/ out
      data tol/1.0e-6/
c
      write(out,*)'     x            fx      dfx'
10     x1 = x
       call func(x, fx, dfx)
       dx = fx / dfx
       x = x1 - dx
       write(out, 102) x1, fx, dfx
      if (abs(dx) .gt. abs(x * tol)) goto 10
      return
102   format(1x, 0pf8.5, 3x, 1p2e12.4)
      end