program FindZeroNewton

  implicit none
  integer :: maxp
  real  :: eps,xc,xt,f,f1
  integer :: i
  
  maxp=200
  eps=.00001
  xt=0.3
  
  do i=1,maxp
     xc=xt-f(xt)/f1(xt)
     if(abs(xc-xt) < eps ) exit
     !  togliere commento per vedere come converge
     write(6,*)'--->',i,xc,abs(xc-xt)
     xt=xc
  enddo
  if(i <= maxp) then
     write(6,*)xc
  else
     write(6,*) 'nessuna soluzione in ',maxp,' passi'
  endif
end program FindZeroNewton

real  function f(x)
  implicit none
  real , INTENT(IN):: x
  f=x**2-1
end function f

real  function f1(x)
  implicit none
  real , INTENT(IN):: x
  f1=2*x
end function f1