1,944 reputation
816
bio website homepages.ulb.ac.be/~samulisi
location Nantes, France
age
visits member for 3 years, 1 month
seen Apr 9 at 21:20

Postdoc working in symplectic/contact topology. I'm currently at the Université de Nantes.


May
23
comment Does this IVP have a unique solution for all $x \in \mathbb R$
Indeed you are correct about the integral, sorry about my mistake there. I don't see how what you wrote addresses uniqueness fully. You are saying that if a solution exists for which $\sin(y)$ is never $0$ and for which $\tan(y/2)$ is never $0$ or undefined, it must satisfy the last displayed equation. Now, this displayed equation does not have unique solutions, so it isn't clear why the uniqueness of the solution to the IVP follows from this. One now needs an argument to say that the $y$ has to stay in the same branch as $Y$ (and deal with the edge cases of $y=0$ etc).
May
23
comment Does this IVP have a unique solution for all $x \in \mathbb R$
There are two problems with this: (1) This doesn't really answer the question asked. The OP wants to know about existence/uniqueness. This doesn't address that. (2) you seem to have a mistake in $\int \frac{1}{sin(y)}\, dy$.
May
23
comment Does this IVP have a unique solution for all $x \in \mathbb R$
Do you know any theorems about existence/uniqueness of solutions for IVP? Some version of : en.wikipedia.org/wiki/Picard–Lindelöf_theorem
May
23
comment Operations on vector spaces
This question is very open-ended... I could write you a linear algebra book and an elementary differential geometry book as an answer. Can you focus the scope a bit? Otherwise, as a starting point for reading up on tangent vectors, differentials, covectors etc, I recommend looking at Spivak's Calculus on Manifolds.
May
18
awarded  Constituent
May
14
comment I just don't see what I do wrong - number of surjections seems higher than number of functions.
If you have a problem with Maple like this, you might want to contact Maple technical support. At the very least, they should be grateful for you finding a bug.
May
14
comment Every manifold admits a vector field with only finitely many zeros
Obtaining a vector field with transverse zeros is (slightly) easier than obtaining the existence of a Morse function. As Ted explained, you want to use Sard's theorem. The idea is much more general -- it allows you to say that you can always arrange the section of a vector bundle to be transverse to the 0 section. Any book on differential topology should explain this -- for instance Hirsch does it.
May
12
revised An alternative description of the first Stiefel-Whitney class
fixed latex display problem
May
10
comment Determining the embedding space:
What do you mean by embedding a usual triangle (or circle) in a sphere? In the case of the circle, you can mean that you take the set of points that are the same (spherical) distance from a given point. I don't know off the top of my head what these geometries are called. A Riemannian geometer should be able to answer this.
May
9
comment Does Differential Topology or Differential Geometry play a larger role in Chaos Theory?
I think that the answer depends a lot on the circumstances special to your situation, e.g. what exactly the courses will cover, what your faculty supervisor [assuming you have one] expects you to know, etc. I think you should talk to your faculty supervisor about this question and/or to the instructors of the two courses in question.
May
7
comment Is there a relation between Super Riemannian manifolds and Kähler manifolds?
@Trimok: why do you think there should be a relationship? did someone mention this in a seminar? do you have some examples in which there is some strange relationship you'd like to generalize? I don't know any physics, so I don't think I can help at all, but I don't even understand where the question is coming from.
May
7
answered Determining the embedding space:
May
7
comment Figure $\infty$ is immersion of circle
@HoseynHeydari: This falls under the heading of things Gowers refers to as "Just Do It" proofs. (See gowers.wordpress.com/2008/08/16/just-do-it-proofs) To get you started: what is the definition of an immersion? Can you obtain a figure X as an immersion from the disjoint union of two intervals? OK, now you are done.
May
7
comment Figure $\infty$ is immersion of circle
@EricO.Korman: I think you are overlooking the fact that he takes the figure $\infty$ to be an immersed circle. It is the image of an injective immersion of $\mathbb{R}$.
May
7
awarded  Revival
May
7
awarded  Caucus
May
7
answered When does a vector field admit orthogonal fields?
May
7
answered An alternative description of the first Stiefel-Whitney class
May
4
comment When does a vector field admit orthogonal fields?
@Yvoz How does this last observation of yours not answer your question? It seems like a characterization of when such a vector field exists. What are you looking for if that isn't the answer?
May
3
comment When does a vector field admit orthogonal fields?
Observe that you don't need orthogonality for the second vector field -- you just need pointwise linearly independent and nowhere vanishing. Then, since $\mathbb{R}^3$ is oriented, you get a third vector field free. You are therefore trying to find a trivialization of the tangent bundle of the quotient of $U$ by the flow of $X$. In general, this quotient will be a horrible space and won't have a tangent bundle, but maybe something can be said anyway. (Note that in your two examples, the quotients are $\mathbb{R}^2$ are $S^2$ respectively, and in particular very nice.)