get_double_occupancy Function

    function get_double_occupancy(ilut, real_sgn) result(double_occ)
        ! function to get the contribution to the double occupancy for a
        ! given determinant, by calculating the
        ! |C_I|^2 *\sum_i <n_iu n_id>/n_spatial_orbs
        integer(n_int), intent(in) :: ilut(0:NIfTot)
        real(dp), intent(in) :: real_sgn(lenof_sign)
        real(dp) :: double_occ
        character(*), parameter :: this_routine = "get_double_occupancy"

        integer :: n_double_orbs
        real(dp) :: frac_double_orbs
        integer(n_int) :: sgn(lenof_sign)

#ifdef CMPLX_
        complex(dp) :: complex_sgn
#endif

        ! here i need to be careful, if it is a double or single run and
        ! stuff
        n_double_orbs = count_double_orbs(ilut(0:nifd))

        ! i only need the fraction of doubly occupied orbitals out of all
        ! spatial orbitals
        frac_double_orbs = 2.0_dp * real(n_double_orbs, dp) / real(nbasis, dp)

        ! now i want to sum in the walkers from the runs..
        ! todo: have to figure out how to access the different runs

        ! extract the walker occupation
#if defined PROG_NUMRUNS_ || defined DOUBLERUN_
        ! i essentially only need two runs!
        double_occ = real_sgn(1) * real_sgn(2) * frac_double_orbs
#else
        double_occ = real_sgn(1)**2 * frac_double_orbs
#endif

    end function get_double_occupancy