Further results for a family of continuous piecewise linear planar maps (2503.02411v1)

Abstract: We consider the family of piecewise linear maps $F(x,y)=\left(|x| - y + a, x - |y| + b\right),$ where $(a,b)\in \mathbb{R}^2$. In our previous work [10], we presented a comprehensive study of this family. In this paper, we give three new results that complement the ones presented in that reference. All them refer to the most interesting and complicated case, $a<0$. For this case, the dynamics of each map is concentrated in a one-dimensional invariant graph that depend on $b$. In [10], we studied the dynamics of the family on these graphs. In particular, we described whether the topological entropy associated with the map on the graph is positive or zero in terms of the parameter $c=-b/a$. Among the results obtained, we found that there are points of discontinuity of the entropy in the transitions from positive to zero entropy. In this paper, as a first result, we present a detailed explicit analysis of the entropy behavior for the case $4<c<8$, which shows the continuity of this transition from positive to zero entropy. As a second result, we prove that for certain values of the parameter $c$, each invariant graph contains a subset of full Lebesgue measure where there are at most three distinct $\omega$-limit sets, which are periodic orbits when $c \in \mathbb{Q}$. Within the framework of the third result, we provide an explicit methodology to obtain accurate rational lower and upper bounds for the values of the parameter $c$ at which the transition from zero to positive entropy occurs.