anchor.diff:  
           use determinants, only: det_info
           use dSFMT_interface, only:  genrand_real2
  -        use excitations, only: calc_pgen_hub_k, excit, create_excited_det, find_excitation_permutation2
  -        use fciqmc_data, only: tau, spawned_walker_dets, spawned_walker_population, spawning_head
  +        use excitations, only: calc_pgen_hub_k, excit, find_excitation_permutation2
  +        use fciqmc_data, only: tau
           use system, only: hub_k_coulomb
  -        use basis, only: basis_length
  -
  -        ! for debug only.
  +
  +! for debug only.
   !        use hamiltonian, only: get_hmatel_k
  +!        use fciqmc_data, only: spawned_walker_dets, spawned_walker_population, spawning_head
   
           type(det_info), intent(in) :: cdet
           integer, intent(in) :: parent_sign
   
           real(p) :: pgen, psuccess, pspawn
           integer :: i, j, a, b, ij_sym, nparticles, s, tmp
  -        integer(i0) :: f_new(basis_length)
           type(excit) :: connection
   
           ! Single excitations are not connected determinants within the 
  
positive.code:                 nparticles = sign(nparticles, parent_sign)
              end if
  
              ! 6. Move to the next position in the spawning array.
              spawning_head = spawning_head + 1
  
              ! 7. Set info in spawning array.
              call create_excited_det(cdet%f, connection, f_new)
              spawned_walker_dets(:,spawning_head) = f_new
              spawned_walker_population(spawning_head) = nparticles
  
  ! Leave the following in for debug reasons...
  ! Should be removed after more testing.
  !            if (abs(get_hmatel_k(cdet%f,f_new)-s*hub_k_coulomb) > 1.e-10) then
  !                write (6,*) 'huh?',get_hmatel_k(cdet%f,f_new), s*hub_k_coulomb,s
  !                write (6,*) cdet%occ_list
  !                write (6,*) i,j,a,b
  !                write (6,*) connection%perm, mod(i-a,2) /= 0
  !                stop
  !            end if
  
  
negative.code:         !    cdet: info on the current determinant (cdet) that we will spawn
          !        from.
  
          use determinants, only: det_info
          use dSFMT_interface, only:  genrand_real2
          use excitations, only: calc_pgen_hub_real, excit, find_excitation_permutation1
          use fciqmc_data, only: tau
          use hamiltonian, only: slater_condon1_hub_real
  
  ! for debug only.
  !        use hamiltonian, only: get_hmatel_real
  !        use fciqmc_data, only: spawned_walker_dets, spawned_walker_population, spawning_head
  
          type(det_info), intent(in) :: cdet
          integer, intent(in) :: parent_sign
  
          real(p) :: pgen, psuccess, pspawn, hmatel
          integer :: i, a, nparticles
          type(excit) :: connection
          integer :: nvirt_avail
  
  