anchor.diff:  
   ! [review] - JSS: RDMs here are DMQMC-specific.  Should there be further dmqmc_data, fciqmc_data,
   ! [review] - JSS: ccmc_data, etc modules?
  +! [review] - NSB: Yes, I think that's sensible.
   
   ! Spawned lists for rdms.
   type rdm_spawn_t
  
positive.code:     ! are considered when finding the spin correlation function, C(r_{i,j}).
      ! All other bits are set to 0. i and j are chosen by the user initially.
      ! [review] - JSS: both input-derived data.
      integer(i0), allocatable :: correlation_mask(:) ! (string_len)
      ! correlation_sites stores the site positions specified by the users
      ! initially (as orbital labels).
  
negative.code:     ! [review] - JSS: encoding/decoding information (perhaps as parameters?)
      ! [review] - JSS: should we have a derived type for a single population and for an
      ! [review] - JSS: array of populations?
      ! [review] - NSB: Perhaps, though might it be slow to extract every population
      ! [review] - NSB: from the array derived type to another derived type? Is this
      ! [review] - NSB: kind of thing you're suggesting.
      ! [review] - NSB: I think that encoding info should be parameters, but at the
      ! [review] - NSB: same time it seems odd having a parameter as a type component.
      ! b) walker population
      ! NOTE:
      !   When using the real_amplitudes option, walker_population stores encoded
  