anchor.diff:  
     call h5gclose_f(solvent_group, error)
   
  +  call tz% norm()
  +  call elem% create_fixed(datafile% observables, 'tz', tz% data)
  +  call elem% create_fixed(datafile% observables, 'tz_count', tz% count)
  +
  +  call h5gclose_f(datafile% observables, error)
  +
     call datafile% close()
   
     call h5close_f(error)
  
positive.code: program setup_fluid
    use cell_system
    use particle_system
    use hilbert
  
negative.code: 
    call solvent% sort(solvent_cells)
  
    wall_v = 0
    do i = 1, 200
       call simple_mpcd_step(solvent, solvent_cells, mt)
       call mpcd_stream(solvent, solvent_cells, 0.1d0)
       call solvent% sort(solvent_cells)
       call solvent_cells%count_particles(solvent% pos)
    end do
  
    do i = 1, 200
       call simple_mpcd_step(solvent, solvent_cells, mt)
       v_com = sum(solvent% vel, dim=2) / size(solvent% vel, dim=2)
  
       call mpcd_stream(solvent, solvent_cells, 0.1d0)
  