anchor.diff:    call neigh% init(colloids% Nmax, 300)
     call neigh% make_stencil(solvent_cells, 1.5d0)
   
  -  call neigh% update_list(colloids, solvent, 1.5d0, solvent_cells)
   
     tau = 0.1d0
     N_MD_steps = 100
     dt = tau / N_MD_steps
  +
  +  skin = 0.8
  +  n_extra_sorting = 0
  +
  +  call neigh% update_list(colloids, solvent, sigma_cut + skin, solvent_cells)
   
     e1 = compute_force(colloids, solvent, neigh, solvent_cells% edges, solvent_colloid_lj)
     e2 = compute_force_n2(colloids, solvent_cells% edges, colloid_lj)
  
positive.code:      end do md
  
       call solvent% sort(solvent_cells)
       call neigh% update_list(colloids, solvent, 1.5d0, solvent_cells)
  
       call simple_mpcd_step(solvent, solvent_cells, mt)
  
  
negative.code:   double precision :: e1, e2
    double precision :: tau, dt
    integer :: N_MD_steps
    integer :: n_extra_sorting
  
    type(mt19937ar_t), target :: mt
  
    double precision :: tmp_x(3)
    double precision :: skin
  
    integer :: i, L(3), seed_size, clock
    integer :: jump(3)
  