anchor.diff:  
     type(h5md_file_t) :: datafile
     type(h5md_element_t) :: elem
  -  type(h5md_element_t) :: e_solvent, e_solvent_v, e_solvent_spec
  +  type(h5md_element_t) :: e_solvent, e_solvent_v, e_solvent_spec, e_solvent_id
     integer(HID_T) :: box_group, solvent_group
   
     integer, parameter :: N = 2000
  
positive.code:      call e_solvent% append(solvent% pos, i, i*tau)
       call e_solvent_v% append(solvent% vel, i, i*tau)
       call e_solvent_spec% append(solvent% species, i, i*tau)
  
       write(13,*) compute_temperature(solvent, solvent_cells, tz), sum(solvent% vel**2)/(3*solvent% Nmax), v_com
  
  
negative.code:   call e_solvent% create_time(solvent_group, 'position', solvent% pos, ior(H5MD_TIME, H5MD_STORE_TIME))
    call e_solvent_v% create_time(solvent_group, 'velocity', solvent% vel, ior(H5MD_TIME, H5MD_STORE_TIME))
    call e_solvent_spec% create_time(solvent_group, 'species', solvent% species, ior(H5MD_TIME, H5MD_STORE_TIME))
    call e_solvent_id% create_time(solvent_group, 'id', solvent% id, ior(H5MD_TIME, H5MD_STORE_TIME))
  
    call solvent% sort(solvent_cells)
    call solvent_cells%count_particles(solvent% pos)
  