message: Core: fixed pairs with negative translations.
  If the translated pair has a periodicity to one of the negative quadrants this is now correctly determined.
  Note: all tranlations which generate the lattice are positive, so negative translations are trivially periodical.
diff: @@ -466,6 +466,12 @@ namespace Utility
  periods_a = (na + pair_da) / Na;
  periods_b = (nb + pair_db) / Nb;
  periods_c = (nc + pair_dc) / Nc;
  +
  + // Catch cases of negative periodicity
  + if (na + pair_da < 0) periods_a = -1;
  + if (nb + pair_db < 0) periods_b = -1;
  + if (nc + pair_dc < 0) periods_c = -1;
  +
  idx_j = pair_j + N*( (((na + pair_da) % Na) + Na) % Na )
  + N*Na*( (((nb + pair_db) % Nb) + Nb) % Nb )
  + N*Na*Nb*( (((nc + pair_dc) % Nc) + Nc) % Nc );
  