c  ***************************************************************
      subroutine juxta(n,index)
c
c Test whether two desinated sites have collided or not.

      implicit double precision(a-h, o-z)
      parameter(maxa=500,maxb=10)
      integer i,j,k,index,n,n2
      common/matrix/x(maxa,3),bangle(maxa)
      common/matrix2/r(maxa,maxa)
      common/Pdl/ nPdl(maxa)
      common/jux_info/djux(maxb),ndis,njux,iset(maxb),
     +	    iflag(maxb,maxb,maxa),njuxtaposed
      common/bf_coords/f(maxa,3),v(maxa,3),u(maxa,3)

      n2 = n/2
      call update_rij(n)
      if (njuxtaposed.eq.1) return
      it1 = 0
      do 100 k = 1, njux
         do 100 i = 1, n
            id = i + iset(k)
            if (id .gt. n) id = id - n
            do 100 j = 1, ndis 
                it1 = 1
               if (r(i,id) .le. djux(j)) then
c                   call cal_dtwist(n,i,id,dtwist)
c                  dtwist=0
c dtwist here =cos(u1,u2)
c                   do iii=1,3
c                    dtwist=dtwist+u(i,iii)*u(id,iii)
c                   enddo
c                   call out_juxtaed(n,i,id)
                 nPdl(iset(k))=nPdl(iset(k))+1
c	         write(*,*) 'nPdL',index,iset(k), nPdl(iset(k))
               if (iflag(j,k,i).eq.1) goto 100    
                      mp = 700+(j-1)*100+iset(k)
                      iflag(j,k,i) = 1
                  write(mp,701) i, id, r(i,id), index
                   call flush(mp)
               endif
100   continue
  
      if (it1 .eq. 0) then
         write(*,*) 'all juxtaposed'
         njuxtaposed=1
      endif

	if (mod(index, 10000).eq.1) then
	 do k=1, njux
	  xxx=1.0*nPdl(iset(k))/n/index
	  write(999,711) iset(k), xxx, index
	 enddo
	  call flush(999)

	endif

701   format(2(1x,i4),1x,f10.4,1x,i10)
711   format(i4,1x,f10.4,1x,i4)


      return
      end


c  ***************************************************************
      subroutine set_juxta(n)

      implicit double precision(a-h, o-z)
      parameter(maxa=500,maxb=10)
      integer i,j,n
      common/matrix/x(maxa,3),r(maxa,maxa),bangle(maxa)
      common/jux_info/djux(maxb),ndis,njux,iset(maxb),
     +      iflag(maxb,maxb,maxa)
      common/Pdl/ nPdl(maxa)
c nPdl save the counts finding a pair separated by dL site juxtaposed

      open(unit=121,file='Input_juxta',status='old')
      read(121,*)ndis
      do i = 1, ndis
         read(121,*) djux(i)
      enddo

      read(121,*)njux
      do i = 1, njux
         read(121,*)iset(i)
         do j = 1, n
            do k = 1, ndis
               iflag(k,i,j) = 0
            enddo
         enddo
      enddo
      
      do i=1, n
         nPdl(i)=0
      enddo

      write(*,*) 'ndistance:',ndis
      write(*,*) 'njux:',njux
      close(121)
      return
      end 

c  ***************************************************************
c cont_juxta  continued trajectory with juxtaposed information

      subroutine cont_juxta(n)

      implicit double precision(a-h, o-z)
      parameter(maxa=500,maxb=10)
      integer i,j,n
      character*20 filename
      common/matrix/x(maxa,3),r(maxa,maxa),bangle(maxa)
      common/jux_info/djux(maxb),ndis,njux,iset(maxb),
     +      iflag(maxb,maxb,maxa)

      write(*,*) 'njux=',njux
      open(unit=112,file='Init_fort',status='unknown')
      
      do k=1,njux
         write(*,*) 'iset',k,iset(k)
            do j=1,ndis
               mp = 700+(j-1)*100+iset(k)
               i11=mp/100;mp=mp-100*i11;i11=i11+48;i12=mp/10+48;i13=49
               filename='fort.'//char(i11)//char(i12)//char(i13)
               read(112,*) n1
               if (n1.ne.0) then 
                  open(unit=111,file=filename,status='unknown')
                  do i1=1,n1
                     read(111,*)  i,j2,x1,j3,x2
                     iflag(j,k,i)=1
                  enddo
                  close(111)
               endif
             enddo
      enddo

      return
      end