anchor.diff:    integer :: n_extra_sorting
     double precision :: kin_co
   
  +  double precision :: conc_z(400)
  +  double precision :: colloid_pos(3,2)
  +
     type(mt19937ar_t), target :: mt
     type(PTo) :: config
   
  
positive.code:     end do
    end subroutine refuel
  
  end program setup_single_dimer
  
negative.code:      call neigh% update_list(colloids, solvent, max_cut+skin, solvent_cells)
  
       call simple_mpcd_step(solvent, solvent_cells, mt)
       
       call refuel
       
       if (modulo(i,100)==0) then
          call concentration_field
          write(16,*) conc_z, colloid_pos
       end if
  
       kin_co = (colloids% mass(1)*sum(colloids% vel(:,1)**2)+ colloids% mass(2)*sum(colloids% vel(:,2)**2))/2
       write(*,'(1i16,6f16.3,1e16.8)') i, e1, e2, &
  