program mnewt_main
      implicit none
c integer n_max to define maximum n
      integer n_max, i, i_again
      parameter (n_max = 16)

c integer for mnewt, n has to be smaller than NP=16
      integer ntrial,n
      parameter (n=2)
      real x(n),tolx,tolf

      write(*,*) 'How many repeating steps for Newton methods ?'
      read(*,*) ntrial
c     write(*,*) 'How many variables is there in your problem ?'
c     read(*,*) n
      write(*,*) 'Please type in x tol and f tol for mnewt :'
      read(*,*) tolx, tolf

 100  write(*,*) 'What is your inital guess on x(i) vector ?'
      read(*,*) (x(i),i=1,n)

      call mnewt(ntrial,x,n,tolx,tolf)

      write(*,*) 'The root vector is :'
      do i=1,n
        write(*,*) x(i)
      end do

 101  write(*,*) 'Find root again ? (1=Yes;0=No)'
      read(*,*) i_again
      if (i_again.eq.1) goto 100
      if (i_again.eq.0) stop
      goto 101

      end



      subroutine usrfun (x,n,NP,fvec,fjac)
      integer n,NP
      real x(n),fvec(NP),fjac(NP,NP)



c     fvec(1) = x(1)**2 + x(2)**2 - 25
c     fvec(2) = x(2)
c     fjac(1,1) = 2*x(1)
c     fjac(2,1) = 0
c     fjac(1,2) = 2*x(2)
c     fjac(2,2) = 1


c     fvec(1) = x(1)**2 - x(2) - 1
c     fvec(2) = x(2)
c     fjac(1,1) = 2*x(1)
c     fjac(2,1) = 0
c     fjac(1,2) = -1
c     fjac(2,2) = 1


c     fvec(1) = x(2) - x(1)
c     fvec(2) = x(2) + x(1)
c     fjac(1,1) = -1
c     fjac(2,1) = 1
c     fjac(1,2) = 1
c     fjac(2,2) = 1


c     fvec(1) = x(2)
c     fvec(2) = x(1)
c     fjac(1,1) = 0
c     fjac(2,1) = 1
c     fjac(1,2) = 1
c     fjac(2,2) = 0

c     fvec(1) = x(1)**2 - 4*x(1) + 4 + x(2)**2 - 25
c     fvec(2) = x(1)**2 + 4*x(1) + 4 + x(2)**2 - 25
c     fjac(1,1) = 2*x(1) - 4
c     fjac(2,1) = 2*x(1) + 4
c     fjac(1,2) = 2*x(2)
c     fjac(2,2) = 2*x(2)

      fvec(1) = x(1)**2 - 4*x(1) + 4 + x(2)**2 - 25
      fvec(2) = x(2)
      fjac(1,1) = 2*x(1) - 4
      fjac(2,1) = 0
      fjac(1,2) = 2*x(2)
      fjac(2,2) = 1

      end