anchor.diff:           call xyz_read_natoms(n,fn_in)
          end if
          rewind(fn_in)
  -       allocate(c(n,3))
  -       allocate(c1(n,3))
  -       allocate(c2(n,3))
  +       allocate(c(3,n))
          allocate(gr(nb))
          allocate(gr0(nb))
          allocate(atag(n))
  
positive.code:        subroutine mask_all(n,c,atag,oc,mid,mtag)
         implicit none
         integer n
         double precision c(n,3)
         character*(*) atag(n)
         logical oc(n)
         integer mid
  
negative.code:          do i2=1,n
             if(oc2(i2)) then
             i = i+1
             rd = c(:,i1)-c(:,i2)
  
             ss = matmul(rlat,rd)
             rr = ss-nint(ss)
  