anchor.diff:           do i2=1,n
              if(oc2(i2)) then
              i = i+1
  -           rd = c(i1,:)-c(i2,:)
  +           rd = c(:,i1)-c(:,i2)
   
              ss = matmul(rlat,rd)
              rr = ss-nint(ss)
  
positive.code:            call xyz_read(n,c,atag,fn_in)
             ok=n.ne.0
           end if
           do i=1,n
             write(88,*) i,(c(i,k),k=1,3)
           end do
           stop
           if(.not.ok) exit
           write(*,*) "number of atoms", n
           oc1=.false.
  
negative.code: 
        end subroutine
  
  