52

I believe it is impossible in general to distinguish questions asked by a graduate student and those asked by a mathematician in a domain in which they are not specialist. Since the latter are allowed on MathOverflow, it would make little sense to disallow the former or relegate them elsewhither. It is hard to argue that MathOverflow receives too many ...

45

I think you ask a quite reasonable question. One certainly could have a more condensed
description of what is on-topic on MathOverflow, and put this in a prominent place where people see it before asking their first question. In particular one could make more clear what is
the difference to Math.SE. As a draft of such description, one could take e.g. the ...

25

I would just like to point out that there are two types of homework questions: graded homework and ungraded homework. In North America, especially at universities with the kind of budget that permits graders and TAs, there is usually a component of the final grade consisting of graded assignments.
But, for example, in parts of Europe and South America, one'...

20

Can someone figure out what is going on in this question about representation varieties of associative algebras? It looks like the OP may have found an error in a published article of Smalø, but I can't prove that its an error.

20

If you have posted a question at MSE and want to cross-post it at MO or the other way around, you can do it under the following conditions:
Wait several days, not just hours. I would suggest a week.
Provide links between the two versions. The MO question should have link to the one at MSE and vice versa. (This is for honesty and avoiding duplicate efforts ...

answered Dec 5 '15 at 19:14

Joonas Ilmavirta

7,44333 gold badges1717 silver badges4545 bronze badges

19

The growth of online tools, such as Math.SE, means that one can no longer base a grade on any work done at home. Quizzes and in-class tests is the way to go.
Now I explicitly allow use of any sources, as long as by the quiz/test time students know the material.
In upper level undergraduate (or lower level graduate) courses my grading method of choice used ...

18

Okay, here's one that I think is interesting and has remained unanswered for over a month. (It might also test out this system.)
Does there exist a bijection of $\mathbb{R}^n$ with itself such that the forward map is connected but the inverse is not?
If it isn't clear from the title, this question (asked by Willie Wong) asks whether the inverse of any ...

18

Waiting a week would usually be considered reasonable.

17

EDIT: Some more information from Catija: This screen element is not currently customizable, so if we wanted it customized, SE would have to implement a new feature. Here Catija indicates that the current SE thinking is that this particular screen element ought to be something which looks the same across the whole SE network. But here she indicates that on ...

17

As a data point for our Stack Exchange overlords, I have twice now tried to migrate a question from math.SE to math.SE because I didn't realize it was already there. I'd really like to get a striking difference in color and background.

16

In my view, your questions are at a good level for MO. A good indication of this is that (as you implicitly point out) you're getting lots of upvotes but almost no answers on MSE.
I like the detail you put into your questions, and I think that will go down well. If you're asking questions as a result of going through textbooks and getting stuck, probably ...

15

There is no formal connection. You may often see the same question on both sites because a lot of people cross-post (manually), a practice which is generally frowned upon, especially when the same question appears at both sites almost simultaneously and the poster doesn't mention anything about cross-posting or doesn't link to the question at the other site. ...

answered Sep 19 '19 at 19:42

15

Cross-posting is discouraged in general, because it can lead to duplication of effort by people answering on different sites. However, it is appropriate under some circumstances.
Most of the advice discussed by Joonas Ilmavirta in the context of cross-posting to Math Stack Exchange is applicable in general. To quote Joonas, if you're considering cross-...

14

This question asks, given a homogenous degree $n$ polynomial map $f: \mathbb{Z}^n \to \mathbb{Z}$, how can we test if it is a norm map from a number field? I know roughly what the answer must be: Over $\mathbb{Q}^{alg}$, $f$ should factor as $n$ distinct hyperplanes and $f$ should be irreducible over $\mathbb{Q}$. That should make $f: \mathbb{Q}^n \to \...

14

It is doubtful that SE would allow another "mathematical" mathematics site to open.
In fact some time ago (2012, so even prior to MO's move to the SE network) there was an Area 51 proposal for a "Postgrad Mathematics" site. The proposal itself has been deleted, but a discussion or two live on. It is highly likely that an SE employee closed it after deeming ...

13

The judgment of whether a question is considered on-topic or not for MO is made by individual MO users. If a question is closed but other users disagree with the reasons for closure, the latter may cast votes to reopen. But there is no blanket answer to your first question. The individuals who voted to close may or may not give their explicit reasons. You ...

answered Nov 23 '20 at 15:24

12

You can flag the post for moderator attention on MSE, choose the free-form flag and ask for a migration to MO.
Another option, which is useful when the crickets really chirp, and you haven't got any comments either, is to simply delete the question and post it anew on MO.

answered May 30 '14 at 15:08

12

If you don't understand the answer, ask in your comments
the person who gave the answer for more explanation. Certainly you don't mark the question as "answered" until you understand. What for?

12

Personal opinion: I think that the current system of having several of separate sites for different math-related topics (apart from MO and MSE, there are also related ones like scientific computing, math educators, history of science...) is not the best one, and adding new sites doesn't help; it just makes the community more fragmented.
Maybe we need tags ...

11

Is there an injective cubic polynomial $\mathbb Z^2\rightarrow\mathbb Z$?
This question asks exactly what its title suggests: is there a polynomial of degree $3$ in $\mathbb Z[x,y]$ whose induced map $\mathbb Z^2\rightarrow\mathbb Z$ is injective? The question is trivial for polynomials of degree $4$ (where the answer is yes) or polynomials of degree $2$ or ...

11

Does the open mapping theorem imply the Baire category theorem?
The open mapping theorem and the Baire category theorem are both theorems of ZFC, but are independent of ZF. Working in ZF, one can (apparently) prove that BCT implies OMT. Does the converse hold in ZF?
This is currently the highest-voted question with the functional-analysis tag.

11

Yes, one should be closed as off-topic, and migrated to the other site, where it can be closed as a duplicate. It's a bit painful that we can't close as a duplicate of a question on another site, but that's the present state of things.
I think the majority of cross-posted questions will be off-topic for MO and on-topic on MSE, but not all. I see you're not ...

11

It makes sense to talk about the core communities of each forum, so that it becomes easier to understand the scope and the differences. Not being active on the mathematics forum, I will give my belief, which hopefully matches the intent, of the community for that forum.
MathOverflow has a community of professional mathematicians employed in academia and ...

10

The reddit website has several forums dedicated to mathematics.
The main math forum has a large audience but there are several others subs such as /r/learnmath, /r/homeworkhelp, /r/cheatatmathhomework, /r/askmath, /r/MathHelp
which are somehow more "finegrained" than mathoverflow/mathstackexchange.
See this link for an extensive list of subreddits dealing ...

10

You have the makings of a good question. To make it acceptable, keep it brief, provide links, and do not add much that is not pertinent.
I will use some of my questions as examples of what to avoid. One of my better questions (37679 on Westzynthius) has the disadvantage of including a lot of "necessary fluff": material I thought was useful to setup the ...

9

Here is a question which seems interesting,
What does it take to divide by $2$?
In a nutshell, we know that in $\sf ZF$, assuming classical logic, we can prove that if $A\times\{0,1\}$ and $B\times\{0,1\}$ are equipotent, then $|A|=|B|$.
How far can this bend before it breaks? Can we do the same in intuitionistic set theories?
(Minor bump: the question ...

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