Period doubling and reducibility in the quasi-periodically forced logistic map

We study the dynamics of the Forced Logistic Map in the cylinder. We compute a bifurcation diagram in terms of the dynamics of the attracting set. Different properties of the attracting set are considered, as the Lyapunov exponent and, in the case of having a periodic invariant curve, its period and its reducibility. This reveals that the parameter values for which the invariant curve doubles its period are contained in regions of the parameter space where the invariant curve is reducible. Then we present two additional studies to explain this fact. In first place we consider the images and the preimages of the critical set (the set where the derivative of the map w.r.t the non-periodic coordinate is equal to zero). Studying these sets we construct constrains in the parameter space for the reducibility of the invariant curve. In second place we consider the reducibility loss of the invariant curve as codimension one bifurcation and we study its interaction with the period doubling bifurcation. This reveals that, if the reducibility loss and the period doubling bifurcation curves meet, they do it in a tangent way

Carleson, Premi Abel 2006

En aquesta nota presentem tres dels treballs més rellevants de Lennart Carleson amb motiu del Premi Abel que va rebre el 2006, que van ser destacats pel comitè.In this note, we present three of the most relevant works of Lennart Carleson. He has been awarded the Abel Prize in 2006 and these particular works were mentioned by the prize committee

Dynamics of the QR-flow for upper Hessenberg real matrices

We investigate the main phase space properties of the QR-flow when restricted to upper Hessenberg matrices. A complete description of the linear behavior of the equilibrium matrices is given. The main result classifies the possible $\alpha$ - and $\omega$-limits of the orbits for this system. Furthermore, we characterize the set of initial matrices for which there is convergence towards an equilibrium matrix. Several numerical examples show the different limit behavior of the orbits and illustrate the theory

Classification of linear skew-products of the complex plane and an affine route to fractalization

Linear skew products of the complex plane, θ↦θ+ω,z↦a(θ)z,} where θ∈T, z∈C, ω/2π is irrational, and [θ↦a(θ)∈C∖{0} is a smooth map, appear naturally when linearizing dynamics around an invariant curve of a quasi-periodically forced complex map. In this paper we study linear and topological equivalence classes of such maps through conjugacies which preserve the skewed structure, relating them to the Lyapunov exponent and the winding number of θ↦a(θ). We analyze the transition between these classes by considering one parameter families of linear skew products. Finally, we show that, under suitable conditions, an affine variation of the maps above has a non-reducible invariant curve that undergoes a fractalization process when the parameter goes to a critical value. This phenomenon of fractalization of invariant curves is known to happen in nonlinear skew products, but it is remarkable that it also occurs in simple systems as the ones we present

Carleson, premi Abel 2006

En aquesta nota presentem tres dels treballs més rellevants de Lennart Carleson amb motiu del Premi Abel que va rebre el 2006, que van ser destacats pel comitè

Classification of linear skew-products of the complex plane and an affine route to fractalization

Linear skew products of the complex plane, \left.\begin{array}{l} \theta \mapsto \theta+\omega \\ z \mapsto a(\theta) z \end{array}\right\} where $\theta \in \mathrm{T}, z \in \mathbb{C}, \frac{\omega}{2 \pi}$ is irrational, and $\theta \mapsto a(\theta) \in \mathbb{C} \backslash\{0\}$ is a smooth map, appear naturally when linearizing dynamics around an invariant curve of a quasi-periodically forced complex map. In this paper we study linear and topological equivalence classes of such maps through conjugacies which preserve the skewed structure, relating them to the Lyapunov exponent and the winding number of $\theta \mapsto a(\theta) .$ We analyze the transition between these classes by considering one parameter families of linear skew products. Finally, we show that, under suitable conditions, an affine variation of the maps above has a non-reducible invariant curve that undergoes a fractalization process when the parameter goes to a critical value. This phenomenon of fractalization of invariant curves is known to happen in nonlinear skew products, but it is remarkable that it also occurs in simple systems as the ones we present