“…From tools that are used in the analysis of nonlinear systems, the most general tools are the frequency response curve 4 , 5 , 11 , 15 , 17 – 21 , 27 , 33 , 34 , 38 , the backbone curve 11 , 12 , 19 and, when the numerical approach is used, time histories 16 , 35 , 43 . In the group of more sophisticated tools, however, more specific techniques can also be mentioned: phase portraits 7 , 8 , 35 – 37 , bifurcation diagrams 8 , 38 , 39 , basins of attraction 40 and Poincaré maps 8 , 35 , 41 , 42 .…”