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. 2012 Jun 7;7(6):e38402. doi: 10.1371/journal.pone.0038402

Figure 6.

Figure 6

(A) Establishment of a coordinate system on the half line Inline graphic with the origin Inline graphic. Here, Inline graphic is the equilibrium point and Inline graphic is transversal to the vector field in the neighborhood of Inline graphic. Note that both Inline graphic and Inline graphic depend continuously on Inline graphic; (B) Curves of the Poincaré map Inline graphic. Each intersection between the curves and the black line Inline graphic corresponds to a fixed point of Inline graphic as well as to a limit cycle of the system (8). For Inline graphicHz, the curve has no intersection with the black line, so that there is no limit cycle. At higher values of Inline graphic, the curve moves upward; it first intersects with the black line at Inline graphic, where a single semi-stable limit cycle emerges. As Inline graphic increases to Inline graphicHz, two bifurcated limit cycles appears. Here, one cycle is stable characterized by the quantity Inline graphic at one fixed point, and the other cycle is unstable with the quantity Inline graphic at the other fixed point.