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Dynamics of flows and maps (continuous and discrete time), including infinite-dimensional dynamics, Hamiltonian dynamics, ergodic theory.
13
votes
Homeomorphism of the circle with rational rotation number
The answer is "yes". Consider $\mathbb S^1$ as the quotient $\mathbb R/\mathbb Z$. Your homeomorphism $f$ lifts to a homeomorphism $\phi : \mathbb R \to \mathbb R$ such that $\phi(x+1)=\phi(x)+1$. For …
5
votes
Are real-analytic functions in $\mathbb{R}^2$ holomorphic after suitable change of coordinates?
To see why the second question cannot have a simple answer, it is sufficient to look at the local context near a fixed-point of a tangent-to-identity mapping, as Alexandre Eremenko suggests. By "a sim …
8
votes
1
answer
864
views
"Explicit" examples of Irrational numbers very well approximated by rational numbers
This question relates to this one and that one.
Some background
In the setting of discrete holomorphic dynamics (say, Julia sets)
an irrational $\lambda$ is said to be well approximated by rational
nu …
2
votes
Accepted
Analyticity of central stable manifolds
Quick answer to the first question: no, there is no reason why it should be analytic. Take e.g. the parametric vector field (written as a Lie derivative)$$X(x,y):=-x^3\partial_x+(y+\alpha x)\partial_y …
5
votes
1
answer
219
views
Orbits space of real-analytic planar foliations
Consider a foliation of $\mathbb{R}^2$, say coming from the trajectories of a vector field $X$. Its orbit space (the quotient of $\mathbb{R}^2$ by the relation "lying on the same trajectory") is seldo …
2
votes
Accepted
Can a holomorphic vector field have an attractor homoclinic loop?
The answer is 'no' for much the same reason that the OP indicates: the existence of a homoclinic or heteroclinic connection implies that neighboring trajectories are periodic.
First, one needs to have …
2
votes
A Leibniz-like formula for $(f(x) \frac{d}{dx})^n f(x)$?
While not pretending to answer the OP, the following is too long to fit in a comment while it might contain elements of interest to the poster.
If $f$ is a convergent object (smooth or analytic), then …
5
votes
Accepted
Planar polynomial vector field for a harmonic pair of polynomials
First, this case is totally uninteresting regarding Hilbert XVI. Indeed, there are no limit cycles in such systems. The $\alpha / \omega$-limit of a trajectory is either a point or a non-isolated cycl …
3
votes
Polynomial vector field tangent to a given analytic simple closed curve
The answer is "no". In fact, it is still "no" for germs of curves : generically, a germ of an analytic curve $\gamma : (\mathbb R,0)\rightarrow (\mathbb R^2,0)$ is not tangent to any polynomial vector …
2
votes
Accepted
A complete classification of linear foliations of $\mathbb{R}^n \setminus \{0\}$
I don't know offhand the answer of your first question, but I can answer the particular situation you describe afterwards : the holonomy is always trivial.
First, notice that a compact leaf $L$ is e …
2
votes
Accepted
The entire parametrization of leaves of singular holomorphic foliation of $\mathbb{C}P^2$
For your first question: $dy=y^2$ can be integrated by quadratures. The solutions are homographies.
For your second question: no it is not true. By the uniformization theorem, the universal covering …
2
votes
Accepted
Periodic orbits in the plane
The period of the compact, non-singular orbit $\gamma$ is given by $$T(\gamma)=\oint_\gamma \tau$$ where $\tau$ is any differential $1$-form such that $\tau(F)=1$, e.g. $\tau:=\frac{\mathrm{d}y_2}{\mu …
0
votes
Accepted
Are codimension one foliations of $\mathbb{R}^{n}-\{0\}$ with compact leaves, stable at origin?
Yes. Let $\mathcal{F}$ be the foliation (of arbitrary dimension in $\{1,\ldots,n-1\}$), which I assume regular and transversely continuous. It is sufficient to consider the case of a ball $V$ of rad …
5
votes
Accepted
Given $g(h(z))$ is convergent, what can be said about the convergence of $g(z)$ and $h(z)$?
If I understand correctly the setting (say $f$ is a germ at $0\in\mathbb C$ of a biholomorphic function), the answer is no in general, but yes generically. The diffeomorphismn $f$ can always be writte …
1
vote
Accepted
Holomorphic vector field with infinite separatrix
No, a lot more vector fields have infinitely many separatrices. They are called «dicritical». For instance, you can change locally the analytic coordinates $(z_1,\ldots,z_n)$, the vector field will no …