anchor.diff:    use interaction
     use hdf5
     use h5md_module
  +  use particle_system_io
     use mpcd
     use threefry_module
     use ParseText
  
positive.code: 
    type(h5md_file_t) :: datafile
    type(h5md_element_t) :: elem
    type(h5md_element_t) :: e_solvent, e_solvent_v
    type(h5md_element_t) :: elem_tz, elem_tz_count, elem_vx_count
    type(h5md_element_t) :: elem_rhoz
    type(h5md_element_t) :: elem_vx
    type(h5md_element_t) :: elem_T
    type(h5md_element_t) :: elem_v_com
    integer(HID_T) :: box_group, solvent_group
  
    integer(c_int64_t) :: seed
    integer :: i, L(3), error, N, n_threads
  
negative.code:         rhoz% data = 0
       end if
  
       call solvent_io%position%append(solvent% pos)
       call solvent_io%image%append(solvent% image)
       call solvent_io%id%append(solvent% id)
       call solvent_io%velocity%append(solvent% vel)
  
    end do
  
    call elem_tz% close()
    call elem_tz_count% close()
    call elem_rhoz% close()
  