anchor.diff:  
     integer, parameter :: block_length = 8
     integer :: n_blocks
  -  type(correlator_t) :: msd, omega_acf, oacf
  +  type(correlator_t) :: msd, omega_acf, oacf, vacf
     integer(HID_T) :: correlator_group, group
   
     double precision :: unit_r(3), omega(3), rel_v(3), norm_xy
  
positive.code:            call dimer_io%image%append(colloids%image)
          end if
  
          com_pos = ( colloids%pos(:,1)+colloids%image(:,1)*solvent_cells%edges + &
               colloids%pos(:,2)+colloids%image(:,2)*solvent_cells%edges)
  
          unit_r = rel_pos(colloids%pos(:,1), colloids%pos(:,2), solvent_cells%edges)
  
negative.code:   call h5md_write_dataset(group, 'count', omega_acf%count)
    call h5md_write_dataset(group, 'step', colloid_sampling)
    call h5md_write_dataset(group, 'time', colloid_sampling*dt)
    call h5gclose_f(group, error)
  
    call h5gcreate_f(correlator_group, 'velocity_autocorrelation', group, error)
    call h5md_write_dataset(group, 'value', vacf%correlation)
    call h5md_write_dataset(group, 'count', vacf%count)
    call h5md_write_dataset(group, 'step', 1)
    call h5md_write_dataset(group, 'time', dt)
    call h5gclose_f(group, error)
  
    call h5gclose_f(correlator_group, error)
  