anchor.diff:                  spawned_walker_population = 0
   
                   ! Consider all walkers.
  -                spawndie: do iwalker = 1, ndets
  +                do iwalker = 1, ndets
   
                       ! Simulate spawning.
  -                    spawning: do ipart = 1, abs(walker_population(iwalker))
  +                    do ipart = 1, abs(walker_population(iwalker))
                           ! Attempt to spawn from the current particle onto all
                           ! connected determinants.
                           call attempt_spawn(iwalker)
  -                    end do spawning
  +                    end do
   
                       call simple_death(iwalker)
   
  -                end do spawndie
  +                end do
   
                   call simple_annihilation()
   
  
positive.code:     subroutine do_simple_fciqmc()
  
          logical :: tVaryShift = .false.
          real(dp) :: shift_damping = 0.050_dp
          integer :: target_particles = 10000
          integer :: ireport, icycle, iwalker, ipart
          integer :: nparticles, nparticles_old
  
negative.code: 
      end subroutine simple_annihilation
  
      subroutine update_shift(nparticles_old, nparticles)
  
          ! Update the shift according to:
          !  shift(beta) = shift(beta-A*tau) - xi*log(N_w(tau)/N_w(beta-A*tau))/(A*tau)
          ! where
          !  shift(beta) is the shift at imaginary time beta,
          !  A*tau is the amount of imaginary time between shift-updates (=ncycles),
          !  xi is a damping factor (0.05-0.10 is appropriate) to prevent large fluctations,
          !  N_w(beta) is the total number of particles at imaginary time beta.
          ! In:
          !    nparticles_old: N_w(beta-A*tau).
          !    nparticles: N_w(beta).
  
          integer, intent(in) :: nparticles_old, nparticles
  
          ! This should be changed into an input option when necessary.
          real(dp) :: shift_damping = 0.050_dp
  
          shift = shift - log(real(nparticles,8)/nparticles_old)*shift_damping/(tau*ncycles)
  
      end subroutine update_shift
  
  end module simple_fciqmc
  