Mathematics

Associated with Math.SE; for both general discussion & math qu...
Aug 26, 2023 22:53
@Jakobian Off topic, but there is a thing called fly screen which is in general effective (I am using tesa.com/en/consumer/tesa-insect-stop-standard-for-windows.html).
Jun 17, 2023 12:08
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Q: Compact set in the order topology

erika21148Let $(X, \leq)$ be a linearly ordered set and let $\mathcal{T}$ denote the order topology on $X$. Prove that $(X, \mathcal{T})$ is compact if and only if every nonempty set of $X$ has a greatest lower bound and a least upper bound. I don't know how to apply the definition of compactness in this t...

Jun 17, 2023 12:03
In general topology, the lexicographic ordering on the unit square (sometimes the dictionary order on the unit square) is a topology on the unit square S, i.e. on the set of points (x,y) in the plane such that 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1. == Construction == The lexicographical ordering gives a total ordering ≺ {\displaystyle \prec } on the points in the unit square: if (x,y) and (u,v) are two points in the square, (x,y) ≺ {\displaystyle \scriptstyle \prec } (u,v) if and only if either x < u or...
Jun 17, 2023 12:00
@ThomasFinley There is a notion called differential forms. You can find many materials via Googling.
Jun 11, 2023 21:42
I recently heard conical smoothness of stratified spaces.
Jun 11, 2023 21:15
@shintuku That seems to be incorrect. You could take c=1 and d=a, then gcd(a,c)=1 and gcd(a,e)=gcd(a,a(b+1))=a.
Jun 11, 2023 21:10
I guess that you could open another room to argue about these?
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Jun 11, 2023 21:08
It is the clearest example of being off-topic.
Jun 10, 2023 20:46
It is impossible. The local homology around a boundary point seems to be different from that around an interior point.
Jun 7, 2023 19:26
@SoumikMukherjee India has 1400 milliards people, which I suppose to have a great diversity.
Jun 7, 2023 18:12
But you have to see why the uniform continuity does not depend on the choice of norm.
May 14, 2023 14:16
@MagnusAlexander I would like to clarify. I guess that there is a difference between every student in Moscow State University (or Moscow School of Economics, say) and "every student in Russia".
May 13, 2023 21:05
@Koro I am not a fan of Hatcher's book. It is a bit too talkative, and not very conceptual.
Apr 11, 2023 15:29
@HashNuke I was mistaken: math.stackexchange.com/a/1786792
Apr 10, 2023 22:02
@HashNuke I guess that this follows from the following: let $H$ be a Hilbert space (maybe also assumed to be separable), and $E,F$ two closed subspaces of $H$. Then the sum $E+F\subseteq H$ is also closed.
Apr 8, 2023 18:04
@Shinrin-Yoku It is a sufficient condition, not necessary. Consider $(y-x)^2=0$.
Apr 8, 2023 16:31
@Shinrin-Yoku There are some other typical examples: $y-x^2(x+1)=0$ at $(0,0)$, and $x^3-y=0$ at $(0,0)$, what about $x=f(y)$
Apr 4, 2023 18:55
I heard that TDA is more related to algebraic topology.
Apr 4, 2023 18:27
I guess that analysis is about inequalities, not only real analysis.
Apr 4, 2023 18:17
And the lecture notes that I see are usually more "complete" than what is covered in a course.
Mar 16, 2023 19:36
@shintuku Under what circumstances will Russia be cornered?
Mar 8, 2023 07:02
@TedShifrin Not even for fields of char 2.
Mar 8, 2023 06:56
@ILikeMathematics Tablets become more common during and after pandemic, since there are more online talks. It is not really something essential, as far as I understand. Do whatever that fits you. However, it seems useful to typeset mathematical notes, say, in graphical tools like TeXmacs and LyX, or LaTeX.
Feb 23, 2023 11:22
@Astyx Maybe you are aware of. There was a course at PCMI: youtube.com/playlist?list=PLldN_DpkXL3Y-ktK5Nq5IYgRbNjYLMNhF
Feb 20, 2023 07:41
@onepotatotwopotato This is something important— not only in number theory, but in algebra.
Jan 23, 2023 17:17
@AlessandroCodenotti It is not compact (it is a TVS), but somehow completely controlled by a compactum.
Jan 23, 2023 15:52
For example, the space of Radon measures on a compact Hausdorff space, with compact-open topology.
Jan 23, 2023 15:47
@AlessandroCodenotti So you prefer Smith spaces to Banach spaces?
Jan 23, 2023 15:44
@Nasser This is listed as a predatory journal beallslist.net and in general, you could look up mathscinet to guest whether a journal is of good quality.
Jan 23, 2023 15:42
@TedShifrin This particular journal is listed as a predatory journal in beallslist.net
Jan 16, 2023 12:57
@Thorgott What do you mean by "in functional analysis, you want the sup"?
Jan 16, 2023 08:05
The Hahn–Banach theorem only needs a real vector space with a sublinear functional.
Jan 16, 2023 07:33
I just learned that the Hahn–Banach theorem can be proved via the Tychonoff theorem for compact Hausdorff spaces.
Jan 14, 2023 21:56
@AlessandroCodenotti I think that this is false. Take a convergent sequence of points.
Jan 13, 2023 18:25
The classification of material is not important, since different schools have different syllabi.
Jan 13, 2023 18:23
That seems enough for elementary functional analysis, unless your functional analysis covers injective/projective tensor products.
Jan 13, 2023 18:22
Quotient spaces?
Jan 13, 2023 18:21
Also tensor products?
Jan 13, 2023 18:16
No, I mean the content.
Jan 13, 2023 18:13
What is graduate level linear algebra?
Jan 13, 2023 18:07
@XanderHenderson I am not familiar with that, but it is basically an ultraproduct of real numbers, thus you can still view them as functions on $\mathbb N$, and modulo an equivalence relation given by an ultrafilter.
Jan 13, 2023 18:05
Maybe Riesz--Markov representation theorem, but it is not always included in elementary functional analysis.
Jan 13, 2023 18:04
I don't remember any.
Jan 13, 2023 18:04
Is there any important theorem in elementary functional analysis which involves Borel measures?
Jan 13, 2023 18:02
What do you want to call infinitesimals?
Jan 13, 2023 18:02
@XanderHenderson It is because you are using $O$, which is a partial order in essence, but one should use "equivalent" infinitesimals (i.e. $\Theta$).
Jan 13, 2023 17:59
The trick is that you only needs some formal property of integrals, and it is very infrequent to play with measure-theoretic constructions.
Jan 13, 2023 17:58
@XanderHenderson You can also see them as an equivalence class of functions, and in that sense (just like how we see objects in L^1), they could be seen as functions. I was not trying to make it completely precise.
Jan 13, 2023 17:56
@XanderHenderson No, I mean the growth of that, so you can compare them via $\ll$, $\gg$ etc.