anchor.diff:          !        and the child determinant, on which progeny are spawned.
           !    trial_func: importance sampling weights.
           ! In/Out:
  -        ! [review] - JSS:  see comments in dmqmc_int_pic_hf_importance_sampling
  -        !    hmatel: on input, untransformed matrix element connecting two spin
  -        !        functions (kets).  On output, transformed matrix element,
  -        !        \Psi^T(cdet%f,cdet%f2) H_{ij} 1/\Psi(f_new,cdet%f2).
  +        !    hmatel: on input, untransformed matrix element connecting two
  +        !        determinants .  On output, transformed matrix element,
  +        !        \Psi^T(cdet%f,cdet%f2) H_I(\alpha)_{ij} 1/\Psi(f_new,cdet%f2).
           !        The factors which the Hamiltonian are multiplied by depend
           !        on the level which we come from, and go to, and so depend on
           !        the two ends of the bitstring we spawn from, and the new
  
positive.code:         ! reducing the probability of spawning to higher excitation levels
          ! between the two ends of the DMQMC bitstring. The exact trial function
          ! used is specified by the users upon input, and stored in the vector
          ! accumulated_probs.
  
          ! This is a wrapper function for using importance sampling with the symmetric version
          ! of the ip-dmqmc algorithm, which also requires the hamiltonian matrix element to be reweighted.
  
negative.code: 
      end subroutine neel_trial_state
  
      subroutine dmqmc_int_pic_free_importance_sampling(sys, cdet, connection, trial_func, hmatel)
  
          ! Apply a transformation to the Hamiltonian matrix element by
          ! reducing the probability of spawning to higher excitation levels
          ! between the two ends of the DMQMC bitstring. The exact trial function
          ! used is specified by the users upon input, and stored in the vector
          ! accumulated_probs. Here we apply the transformation to the interaction
          ! picture Hamiltonian, where H^0 = T.
  
  
          ! This is a wrapper function for using importance sampling with the symmetric version
          ! of the ip-dmqmc algorithm, which also requires the Hamiltonian matrix element to be reweighted.
  