program testnewton
      implicit none
      integer i
      double precision x,f0,f1,func,recider
      x=-1.5d0
      do i=1,200
        f0=func(x)
        write(*,*)i,x,f0
        pause

        f1=func(x+f0)
        recider=f0/(f1-f0)
        x=x-recider*f0
      enddo

      end
    
      double precision function func(x)
      double precision x
      func=x-(x*x+1.0d0)/2.0d0
!x^2-2*x+1=0
      return
      end