anchor.diff:    double precision :: v_com(3), wall_v(3,2), wall_t(2)
     double precision :: gravity_field(3)
     double precision :: T, set_temperature, tau
  +  double precision :: alpha
     logical :: thermostat
   
     call PTparse(config,get_input_filename(),11)
  
positive.code:      call solvent% sort(solvent_cells)
       call wall_mpcd_step(solvent, solvent_cells, state, &
            wall_temperature=wall_t, wall_v=wall_v, wall_n=[rho, rho], thermostat=thermostat, &
            bulk_temperature=set_temperature)
    end do
  
    do i = 1, N_loop
  
negative.code:      call solvent% sort(solvent_cells)
       call wall_mpcd_step(solvent, solvent_cells, state, &
            wall_temperature=wall_t, wall_v=wall_v, wall_n=[rho, rho], thermostat=thermostat, &
            bulk_temperature=set_temperature, alpha=alpha)
       v_com = sum(solvent% vel, dim=2) / size(solvent% vel, dim=2)
  
  
  