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8:13 AM
How do you select an interesting and reasonable problem for a student? I have removed . Would maybe fit here? I was considering , too - but I think that one is less suitable.
82
Q: How do you select an interesting and reasonable problem for a student?

Gordon RoyleI am interested in how to select interesting yet reasonable problems for students to work on, either at Honours (that is, a research-based single year immediately after a degree) or PhD. By this I mean a problem that is unsolved but for which there is a good chance that a student can solve it e...

 
 
2 hours later…
9:51 AM
@TheAmplitwist The trackbacks seem to be working fine with the new format, so all is good.
 
10:37 AM
@TheAmplitwist So this means that there is basically nothing to fix. But I have at least mentioned this on Meta Stack Exchange (in the question "Could the citation helper include DOI-links as https rather than http?"):
> Added later: It seems that recently zbMATH change the format of their links from https://zbmath.org/?q=an:1237.68242 to https://zbmath.org/1237.68242. (The latter is the link you'll get from their website.) But since the old links still work, this isn't really an issue.
 
 
2 hours later…
12:08 PM
It's good that you mentioned it anyway, in my opinion. Whenever the citation helper gets updated, the update can be made thorough.
 
 
3 hours later…
3:11 PM
I should mention a change in the use by the community of this tag: out of 353 current (=non-deleted) questions tagged tag-removed, only 17 have been created since 2014 and only 2 (both closed) since 2018. The current use seems to have more or less converged to: only use this tag when removing tags without leaving other tags, and only when the question is highly off-topic and very likely to be deleted, and is no longer used to remove an irrelevant tag from an a priori reasonable question. — YCor 51 mins ago
@YCor I have to admit that I do not see what you describe as a change.
As far as I can tell, what you describe agrees with the use by regular users in the past.
For example, if I look at quid's answer from 2013:
1
A: 'Tag-removed' tags where they possibly shouldn't be

user9072The usage of tag-removed was two-fold: as an 'empty' tag for massively off-topic and mistagged questions. as a tool to 'delete' tags via merging them into it. Due to the second use-case numerous legitimate questions also got this tag. I think it could make sense to go over this list and reta...

But there is (or was) separate use case for moderators - as described in various posts or here in chat.
Sep 12, 2014 at 14:23, by François G. Dorais
@MartinSleziak The tag info describes the only use case for regular users. It's used for cleaning up tags without bumping by moderators. When a question with that tag pops up on the front page, remove it.
So only the mods are able to tell whether or not they plan to use for merging in the future or not.
I do not know about a more recent merging than . (At some point in 2013.)
Oh, I see there was .
Nov 16, 2018 at 8:23, by Martin Sleziak
I have noticed another tag which has been removed . (In the MO-style burninantion-like non-standard removal; i.e., replaced by .) I don't think there was a discussion on meta about this. (And if there was I have missed it.)
So perhaps the merging of into was the most recent case when the moderators used this tag for that purpose?
 
3:48 PM
@MartinSleziak It may be that my English is too poor to make myself clear :( My point is that almost all current non-deleted questions with the tag have been created before 2014. How do you interpret this?
 
Of course, from the viewpoint of the tags, it is more important when the tag was added rather when the question was created.
I agree that the moderators probably haven't used this as a target for merging since 2018.
But the nature of tag-merging means the we cannot find out from the current state when the tags were actually merged. (Since merging rewrites the revision history.)
We only see the the difference if the question together with the tags was saved somewhere.
Dec 8 at 4:33, by Martin Sleziak
Posts where was added/removed (with editors): https://data.stackexchange.com/mathoverflow/query/1105163/questions-which-had-the-given-tag-including-the-editor-who-added-it?tagname=tag-removed https://data.stackexchange.com/mathoverflow/query/1038474/questions-which-no-longer-have-the-given-tag-including-the-editor?tagName=tag-removed
@YCor I do not know whether you're trying to say something mainly about the usage of this tag by regular users or by moderators.
And definitely the problem is not with your poor English - compared to most MO users, my language skills are abysmal.
I still think that the most occurrences of the tag on the site (among the questions which are not deleted) come from merging by mods - and not from tags added by regular users.
I will use as an example again. Let us say that there was approximately 50 questions with this tag in 2013.
That means that after the merging, the number of occurrences of jumped up by 50 - but the tag which was added by a user was actually , it was an action by a moderator that changed it to .
It seems that for it was between 5 and 10 questions.
 
4:13 PM
2 days ago, by Martin Sleziak
Removals of per month: https://data.stackexchange.com/mathoverflow/query/1186177/number-of-removals-of-the-given-tag-per-month?tagname=tag-removed#graph
2 days ago, by Martin Sleziak
user image
Looking at the graph with removals, it seems that Andrés E. Caicedo edited quite a few occurrences of this tag in 2014 - but then stopped.
@YCor: When you wrote ""and is no longer used to remove an irrelevant tag from an a priori reasonable question", did you mean the usage by moderators by this part?
I agree that the data you found indicate that most likely the mods did not use this tag as the target for merging for some time.
Records of merging aren't publicly shown - but it is quite probably that when some tag is merged, it influences at least some questions which weren't too old at the time.
 
@MartinSleziak No, I mean the usage in general. Indeed, I believe that moderators have stopped adding this tag in the last 8 years.
 
With the exception of some 5 or 10 questions in 2018?
That one was definitely done by the moderators.
So let us say "4 years" instead of "8 years" - and this is very likely true.
But we haven't heard anything from moderators - we do not know whether they intend to use this in the future or not.
 
@MartinSleziak The only question created in 2018 with this tag is mathoverflow.net/questions/310666. From what I see the question seems to have been created with the tag, but I may miss something. In any case the record of creation since 2014 (included) is very small, so this makes 9 years (2014-2022). Which "5 or 10 questions in 2018" do you have in mind?
 
The question which were tagged .
As you can see here, there were several questions tagged back in September 2018. (Only a few.): chat.stackexchange.com/transcript/10243/2018/9/10
Sep 10, 2018 at 4:01, by Martin Sleziak
1
Q: Exact solution of a particular system of non-linear equations (re-formulated to matrix equation)

DragonI have this system of $n$ non-linear equations in $n$ unknowns, arising out of my research problem. Given that $x_0=1$, I have to solve for $(x_1,x_2,\ldots,x_n).$ $$\sum_{i=0}^n x_i^2+2\sum_{j=1}^n\sum_{i=0}^{n-j}x_ix_{i+j}=1$$ $$\sum_{j=1}^n\sum_{i=0}^{n-j}~j^2~x_ix_{i+j}=0$$ $$\sum_{j=1}^n\sum...

Sep 10, 2018 at 4:02, by Martin Sleziak
7
Q: Is there a closed-form solution for $\frac{dy}{dx} = 1 + \frac{a}{y} + \frac{b}{x}$?

PaichuI am looking for an exact solution for the following special case of Chini Equation with $2\geq a > 1 > b > 0, x, y \in \mathbb{R}^+$, $$\frac{dy}{dx} = 1 + \frac{a}{y} + \frac{b}{x}$$ I have tried to approach this using multiple methods and substitutions, but none has gotten me far. I know tha...

Sep 10, 2018 at 4:02, by Martin Sleziak
2
Q: Mathematica/Matlab/other for calculating Onsager's exact solution to the 2d Ising model

endianWould anybody be able to share a Mathematica/Matlab/other script for calculating Onsager's exact solution for the magnetisation of the 2d Ising model? I would be most grateful of one in order to test my MC simulations of the system.

Sep 10, 2018 at 4:02, by Martin Sleziak
1
Q: Exact solution to nonlinear differential equation sought

LorkiI am looking for an exact solution to equation: $w''=aw^{-1/3}+b[f(y)]w^{-5/3}$, where $w=w(y), f(y)$ - arbitrary function (in this case $y^n$ with arbitrary $n$); $a,b$ - constants. Of course I can solve it using numerical methods for certain initial conditions, but I was looking for a exact s...

Sep 10, 2018 at 4:02, by Martin Sleziak
4
Q: Exact solutions to nonlinear Klein-Gordon equation

JonThe nonlinear pde $$ \partial_t^2\phi-\partial_x^2\phi+\lambda\phi^3=0 $$ has the exact solution $$ \phi(x,t)=\mu\left(\frac{2}{\lambda}\right)^\frac{1}{4}{\rm sn}(p_0t-p\cdot x+\varphi,i) $$ with $\mu$ and $\varphi$ two integration constants and sn the snoidal Jacobi function, provided the...

Sep 10, 2018 at 4:02, by Martin Sleziak
3
Q: Ansätze for solving PDEs with wavelets

vonjdIt is common to solve PDEs with e.g. Fourier and Laplace Transforms. It is often said that Wavelets are a progression compared to them with many nice features. My question: Which Ansätze do you know to solve PDEs with Wavelets? Are these solution methods actually superior to the classical Ansätz...

All of the questions mentioned above are now tagged
2
Q: Exact solution of a particular system of non-linear equations (re-formulated to matrix equation)

firestormI have this system of $n$ non-linear equations in $n$ unknowns, arising out of my research problem. Given that $x_0=1$, I have to solve for $(x_1,x_2,\ldots,x_n).$ $$\sum_{i=0}^n x_i^2+2\sum_{j=1}^n\sum_{i=0}^{n-j}x_ix_{i+j}=1$$ $$\sum_{j=1}^n\sum_{i=0}^{n-j}~j^2~x_ix_{i+j}=0$$ $$\sum_{j=1}^n\sum...

8
Q: Is there a closed-form solution for $\frac{dy}{dx} = 1 + \frac{a}{y} + \frac{b}{x}$?

PaichuI am looking for an exact solution for the following special case of Chini Equation with $2\geq a > 1 > b > 0, x, y \in \mathbb{R}^+$, $$\frac{dy}{dx} = 1 + \frac{a}{y} + \frac{b}{x}$$ I have tried to approach this using multiple methods and substitutions, but none has gotten me far. I know tha...

1
Q: Exact solution to nonlinear differential equation sought

LorkiI am looking for an exact solution to equation: $w''=aw^{-1/3}+b[f(y)]w^{-5/3}$, where $w=w(y), f(y)$ - arbitrary function (in this case $y^n$ with arbitrary $n$); $a,b$ - constants. Of course I can solve it using numerical methods for certain initial conditions, but I was looking for a exact s...

4
Q: Exact solutions to nonlinear Klein-Gordon equation

JonThe nonlinear pde $$ \partial_t^2\phi-\partial_x^2\phi+\lambda\phi^3=0 $$ has the exact solution $$ \phi(x,t)=\mu\left(\frac{2}{\lambda}\right)^\frac{1}{4}{\rm sn}(p_0t-p\cdot x+\varphi,i) $$ with $\mu$ and $\varphi$ two integration constants and sn the snoidal Jacobi function, provided the...

4
Q: Ansätze for solving PDEs with wavelets

vonjdIt is common to solve PDEs with e.g. Fourier and Laplace Transforms. It is often said that Wavelets are a progression compared to them with many nice features. My question: Which Ansätze do you know to solve PDEs with Wavelets? Are these solution methods actually superior to the classical Ansätz...

0
Q: Background on the functional equation $F(x+1)+F(x)=f(x)‎$

soodehMehboodiIn the theory of indefinite sums, anti-differences and finite calculus, ‎the following ‎difference ‎functional ‎equation ‎and ‎its ‎solutions ‎are ‎very ‎important: ‎$$‎\bigtriangleup ‎F(x):=F(x+1)-F(x)=f(x) ‎\quad‎\quad‎(1),‎$$ where‎ ‎$‎\bigtriangleup‎$ ‎is ‎the ‎forward ‎difference ‎operato...

And if you check the revision history, it doesn't show . (It shows .)
So this means that at some point after 10 September 2018, the mods merged into . This changed the tags at least on the 6 questions linked above - and on all other questions tagged which existed at the time.
But very probably, it wasn't more than 10 questions.
In short, it is clear that the moderators used merging into tag in September 2018 or later.
I agree that very likely they haven't use it after that very likely this might have been the most recent instance of merging into .
And, of course, there are many deleted questions with this tag. But it's quite possible the recent ones were added by regular users (and aren't a result of merging).
 

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