Trajectories in the phase-space diagrams of the planetary eccentricities e_b and e_c vs. the apsidal alignment angle Δϖ = ϖ_b –ϖ_c for the GJ 1148 system constructed from the octupole-level secular perturbation theory, with GR correction included, assuming the same total angular momentum. Blue crosses indicate the N-body best-fit parameters of e_b, e_c and ϖ_b –ϖ_c and their uncertainties, while the red paths represent the trajectories starting at the best fit. The blue dotted lines represent the maximum planetary eccentricities, which can be attained for the total angular momentum of the system.