get_exact_spectrum Subroutine

    subroutine get_exact_spectrum()

        integer :: lwork, info, ndets
        real(dp), allocatable :: work(:)
        ! Data for the testsuite to use.
        real(dp) :: h_sum, spec_low, spec_high

        call init_exact_spectrum(ndets)

        h_sum = sum(hamiltonian)

        ! Create the workspace for dsyev.
        lwork = max(1, 3 * ndets - 1)
        allocate(work(lwork))

        write(stdout, '(1x,a28)', advance='no') "Diagonalising Hamiltonian..."
        call neci_flush(stdout)

        ! Perform the diagonalisation.
        call dsyev('V', 'U', ndets, hamiltonian, ndets, eigv_es, work, lwork, info)

        write(stdout, '(1x,a9,/)') "Complete."
        call neci_flush(stdout)

        trans_amps_right = matmul(pert_ground_right, hamiltonian)
        trans_amps_left = matmul(pert_ground_left, hamiltonian)

        call output_spectrum(ndets, eigv_es, spec_low, spec_high)

        call write_exact_spec_testsuite_data(h_sum, spec_low, spec_high)

        call end_exact_spectrum()

        deallocate(work)

    end subroutine get_exact_spectrum