encode_sign_rdm Subroutine

    pure subroutine encode_sign_rdm(rdm_entry, real_sign)

        ! Take the real RDM elements stored in real_sign, and encode them
        ! as integers with kind int_rdm, and then place these encoded signs in
        ! the positive elements of the rdm_entry array (the 0'th element
        ! contains the encoded spin orbital labels).

        integer(int_rdm), intent(inout) :: rdm_entry(0:)
        real(dp), intent(in) :: real_sign(1:size(rdm_entry) - 1)
        integer(int_rdm) :: int_sign(1:size(rdm_entry) - 1)

        int_sign = transfer(real_sign, int_sign)
        rdm_entry(1:size(int_sign)) = int_sign

    end subroutine encode_sign_rdm