get_helement_rs_hub_ex_mat Function

    function get_helement_rs_hub_ex_mat(nI, ic, ex, tpar) result(hel)
        integer, intent(in) :: nI(nel)
        integer, intent(in) :: ic, ex(2, ic)
        logical, intent(in) :: tpar
        HElement_t(dp) :: hel

        if (ic == 0) then
            ! diagonal matrix element -> sum over doubly occupied orbitals!
            hel = get_diag_helemen_rs_hub(nI)

        else if (ic == 1) then
            ! one-body operator:
            ! here we need to make the distinction, if we are doing a
            ! transcorrelated hamiltonian or not
            hel = get_offdiag_helement_rs_hub(nI, ex(:, 1), tpar)

        else if (ic == 2 .and. t_trans_corr_hop) then
            hel = get_double_helem_rs_hub_transcorr(ex, tpar)

        else
            ! zero matrix element!
            hel = h_cast(0.0_dp)

        end if

    end function get_helement_rs_hub_ex_mat