fill_spawn_rdm_diag Subroutine

    subroutine fill_spawn_rdm_diag(spawn, nI, full_sign)

        use rdm_data_utils, only: add_to_rdm_spawn_t
        use SystemData, only: nel

        type(rdm_spawn_t), intent(inout) :: spawn
        integer, intent(in) :: nI(nel)
        real(dp), intent(in) :: full_sign(spawn%rdm_send%sign_length)

        integer :: iel, jel

        ! Looking at elements of the type Gamma(i,j,i,j).
        do iel = 1, nel - 1
            do jel = iel + 1, nel
                associate(i => nI(iel), j => nI(jel))
                    call add_to_rdm_spawn_t(spawn, i, j, i, j, full_sign, .false.)
                end associate
            end do
        end do

    end subroutine fill_spawn_rdm_diag