anchor.diff:              call stop_all(this, 'The instantaneous_rdm option must be used in order to calculate the Renyi-2 entropy.')
           if (doing_dmqmc_calc(dmqmc_full_r2) .and. (.not. dmqmc_in%replica_tricks)) &
               call stop_all(this, 'The replica_tricks option must be used in order to calculate the Renyi-2 entropy.')
  +        if (doing_dmqmc_calc(dmqmc_HI_energy) .and. (.not. dmqmc_in%symmetric)) &
  +            call stop_all(this, 'Evaluation of interaction picture Hamiltonian only possible when using symmetric algorithm.')
   
           if (dmqmc_in%all_spin_sectors) then
               if (abs(sys%heisenberg%magnetic_field) > depsilon .or. &
  
positive.code:             if (dmqmc_in%rdm%calc_ground_rdm .or. dmqmc_in%rdm%calc_inst_rdm) &
                  call stop_all(this,'The calculation of reduced density matrices is not supported for this system.')
          end if
  
          if (allocated(dmqmc_in%correlation_sites)) then
              if (size(dmqmc_in%correlation_sites) /= 2) &
  
negative.code:         !   sys: system being studied.
          !   dmqmc_in: DMQMC options.
  
          use system, only: sys_t, heisenberg, ueg
          use dmqmc_data, only: dmqmc_in_t
          use calc, only: dmqmc_rdm_r2, doing_dmqmc_calc, dmqmc_full_r2
          use calc, only: dmqmc_staggered_magnetisation, dmqmc_energy_squared, dmqmc_correlation
          use calc, only: dmqmc_potential_energy, dmqmc_kinetic_energy, dmqmc_HI_energy
  
          use errors, only: stop_all
          use const, only: depsilon, p
  