gen_excit_back_spawn_ueg_new Subroutine

    subroutine gen_excit_back_spawn_ueg_new(nI, ilutI, nJ, ilutJ, exFlag, ic, &
                                            ExcitMat, tParity, pgen, HelGen, store, part_type)
        integer, intent(in) :: nI(nel), exFlag
        integer(n_int), intent(in) :: ilutI(0:niftot)
        integer, intent(out) :: nJ(nel), ic, ExcitMat(2, maxExcit)
        integer(n_int), intent(out) :: ilutJ(0:niftot)
        logical, intent(out) :: tParity
        real(dp), intent(out) :: pgen
        HElement_t(dp), intent(out) :: HElGen
        type(excit_gen_store_type), intent(inout), target :: store
        integer, intent(in), optional :: part_type
        character(*), parameter :: this_routine = "gen_excit_back_spawn_ueg_new"

        integer :: iUnused

#ifdef DEBUG_
        real(dp) :: pgen2
        HElement_t(dp) :: temp_hel
#endif

        HelGen = 0.0_dp
        iUnused = exFlag
        iUnused = store%nopen

        ic = 2

        ! do i want to implement both old and new back spawn??
        ! no!
        if ((t_back_spawn_flex .or. t_back_spawn) .and. &
            (.not. test_flag(ilutI, get_initiator_flag(part_type)))) then

            call gen_double_back_spawn_ueg_new(nI, ilutI, part_type, nJ, ilutJ, tParity, &
                                               ExcitMat, pgen)

#ifdef DEBUG_
            if (.not. IsNullDet(nJ)) then
                pgen2 = calc_pgen_back_spawn_ueg_new(nI, ilutI, ExcitMat, ic, part_type)
                if (abs(pgen - pgen2) > 1.0e-6_dp) then
                    if (tHPHF) then
                        print *, "due to circular dependence, no matrix element calc possible!"
                        temp_hel = 0.0_dp
                    else
                        temp_hel = get_helement(nI, nJ, ilutI, ilutJ)
                    end if

                    write(stdout, *) 'Calculated and actual pgens differ. for non-initiator'
                    write(stdout, *) 'This will break HPHF calculations'
                    write(stdout, *) 'reference det: '
                    call write_det(stdout, projedet(:, part_type_to_run(part_type)), .true.)
                    call write_det(stdout, nI, .false.)
                    write(stdout, '(" --> ")', advance='no')
                    call write_det(stdout, nJ, .true.)
                    write(stdout, *) 'Excitation matrix: ', ExcitMat(1, 1:ic), '-->', &
                        ExcitMat(2, 1:ic)
                    write(stdout, *) 'Generated pGen:  ', pgen
                    write(stdout, *) 'Calculated pGen: ', pgen2
                    write(stdout, *) 'matrix element: ', temp_hel
                    call stop_all(this_routine, "Invalid pGen")
                end if
            end if
#endif
        else

            call gen_double_ueg(nI, ilutI, nJ, ilutJ, tParity, ExcitMat, pgen)

#ifdef DEBUG_
            if (.not. IsNullDet(nJ)) then
                pgen2 = calc_pgen_ueg(ilutI, ExcitMat, ic)
                if (abs(pgen - pgen2) > 1.0e-6_dp) then
                    if (tHPHF) then
                        print *, "due to circular dependence, no matrix element calc possible!"
!                         temp_hel = hphf_off_diag_helement(nI,nJ,ilutI,ilutJ)
                        temp_hel = 0.0_dp
                    else
                        temp_hel = get_helement(nI, nJ, ilutI, ilutJ)
                    end if

                    write(stdout, *) 'Calculated and actual pgens differ. for non-initiator'
                    write(stdout, *) 'This will break HPHF calculations'
                    call write_det(stdout, nI, .false.)
                    write(stdout, '(" --> ")', advance='no')
                    call write_det(stdout, nJ, .true.)
                    write(stdout, *) 'Excitation matrix: ', ExcitMat(1, 1:ic), '-->', &
                        ExcitMat(2, 1:ic)
                    write(stdout, *) 'Generated pGen:  ', pgen
                    write(stdout, *) 'Calculated pGen: ', pgen2
                    write(stdout, *) 'matrix element: ', temp_hel
                    call stop_all(this_routine, "Invalid pGen")
                end if
            end if
#endif
        end if

    end subroutine gen_excit_back_spawn_ueg_new