anchor.diff:    type(h5md_element_t) :: n_solvent_el, catalytic_change_el, bulk_change_el
   
     double precision :: colloid_pos(3,2)
  +  double precision :: com_pos(3)
     type(h5md_file_t) :: hfile
     type(h5md_element_t) :: dummy_element
     integer(HID_T) :: fields_group, params_group
  
positive.code:                  write(*,*) 'on_track', on_track
                end if
             end if
          end if
  
          if ((.not. on_track) .and. (buffer_length/=0))then
  
negative.code:               end if
             end do
          end if
  
          so_max = solvent% maximum_displacement()
          co_max = colloids% maximum_displacement()
  