Pearl Dive

A meeting place for sponsors and excellent posts. See https://math.meta.stackexchange.com/q/31105/11619
5d ago – Martin Sleziak
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Oct 31, 2020 11:17
5
Q: About the roots of the derivative of a special polynomial

Maurizio BarbatoLet $p$ be an odd prime, and let $n_1,\dots,n_{p-2}, m$ be even integers such that $n_1 < n_2 < \dots < n_{p-2}$ and \begin{equation} 2m > \sum_{i=1}^{p-2} n_i^2. \end{equation} Consider the polynomial \begin{equation} g(x)=(x^2 + m)(x - n_1) \dots (x - n_{p-2}). \end{equation} From Rolle's Theor...

Oct 30, 2020 19:30
@Integrand flexing is allowed :)
Oct 1, 2020 18:10
Misha Lavrov generously put up a bounty for this fun question about determinants
Sil
Aug 13, 2020 21:48
3
Q: Infinitely many solutions leads to existence of a polynomial

user591814Let $P$ and $Q$ be monic polynomials with integer coefficients and degrees $n$ and $d$ respectively, where $d\mid n$. Suppose there are infinitely many pairs of positive integers $(a,b)$ for which $P(a)=Q(b)$. I would like to determine if exists a polynomial $R$ with integer coefficients such t...

Aug 1, 2020 19:30
@CalumGilhooley My pleasure. Great work.
Aug 1, 2020 16:57
@JonathanZsupportsMonicaC I awarded one of them just now, the new one I will do in 24 hours (there's a time limit on how fast you can award a bounty).
Jul 28, 2020 16:37
@AlexanderGruber Hey, it looks like I'm about to get an answer on the question you're helping me with. I've been talking to a Mr Gilhooley in the comments, and he showed me a graph that does the trick. I guess he'll post an answer with an explanation, and then I don't know what. Let me know if I need to do anything
Jul 25, 2020 06:35
There's more, but that would be off-topic in this room. I just wanted to give an explanation as to why I didn't let that bounty run full time.
Jul 25, 2020 06:34
@TobiasKildetoft I cut that bounty short. Sorry about not giving you much time. The OP posted one answer, citing an old paper. Combined with one earlier question from the same OP I got bad vibe out of it. It looks as if they wanted to post that as a challenge rather than a genuine question. That OP also complained loudly in meta (in a thread they later deleted) about a few downvotes, and how they are more of an expert in algebra than anyone on this site.
Jul 25, 2020 04:47
Jyrki has done an excellent job pushing it forward. I give him as much credit as myself on it.
Jul 18, 2020 22:10
118
Q: Is There An Injective Cubic Polynomial $\mathbb Z^2 \rightarrow \mathbb Z$?

Milo BrandtEarlier, I was curious about whether a polynomial mapping $\mathbb Z^2\rightarrow\mathbb Z$ could be injective, and if so, what the minimum degree of such a polynomial could be. I've managed to construct such a quartic and rule out the existence of such a quadratic, but this leaves open the quest...

Apr 22, 2020 15:41
1 message moved to ­Trash
Apr 11, 2020 16:36
@Shaun I'm just checking in to keep the room going :)
Mar 9, 2020 12:41
I would like to nominate math.stackexchange.com/questions/3506310/…, which is a rather unmotivated but still very interesting question.
Feb 16, 2020 21:22
5
Q: Semidirect product action and its geometry

Siddharth BhatI'm going by the maxim Groups, like men, are known by their actions This naturally leads one to ask "given groups $G, H$ which act on sets $S, T$ and the semidirect product $G \rtimes H$, how does one visualize the action of $G \rtimes H$? What does it act on? Some combination of $S$ and $T...

Feb 15, 2020 09:55
I guess this question on meta is (to some extent) related to the reasons why this room was created: Why “reward existing answers” bounties grouped with the rest of the bounties.
Sil
Feb 12, 2020 22:02
Can anybody confirm whether the answer with bounty on this question math.stackexchange.com/questions/2827702/… is correct? It seems suspicious to me, but I am not sure (even if it is correct, it would be nice to have some alternative answers).
Feb 6, 2020 12:22
Feb 6, 2020 09:02
BTW it seems that convexity of the LHS and the RHS alone is not sufficient to show that there are at most two solutions: How many times can strictly convex functions intersect?
Feb 1, 2020 12:04
6
Q: Can $\operatorname{Re}(a+bi)^{n}$ be overlapped with $a,b\in\mathbb{Z}$ fixed?

dodicta Is there any integer solution for $$\operatorname{Re}((a+bi)^{m})=\operatorname{Re}((a+bi)^{n})$$ except $(m,n)=(1,3)$, where $0\leq m<n,\ |a|\neq |b|,\ a\neq 0,\ b\neq 0$? In other words, Can $\operatorname{Re}(a+bi)^{n}$ be overlapped with $a+bi\in\mathbb{Z}[i]$ fixed? This is a ge...

Jan 31, 2020 16:18
Hi @Mary.
Jan 26, 2020 08:26
7
Q: Cell decomposition for $\mathbb{C}P^n$ that has $\mathbb{R}P^n$ as a subcomplex?

Ben Blum-SmithReal projective space $\mathbb{R}P^n$ embeds in a natural way in complex projective space $\mathbb{C}P^n$. (Using standard projective coordinates on $\mathbb{C}P^n$, $\mathbb{R}P^n$ is the subspace consisting of points that have a representative in which all coordinates are real.) I know (very ...

Sil
Jan 23, 2020 07:44
@JyrkiLahtonen Actually I think it is good idea to have this summary somewhere (I was looking for it as well), but I am not sure if a chat is the best place since you willl have to read the whole chat history to find all... But what are the alternatives? Putting it into a meta post might make that post updated too often, which some users could dislike...
Sil
Jan 18, 2020 08:21
3
Q: 2D Random Walk Hitting Time

Hang WuSuppose there is a grid $[1,N]^2$. A person standing at some initial point $(x_0,y_0)$ walk randomly within the grid. At each location, he/she walks to a neighboring location with equal probability (e.g., for an interior point, the probability is $\frac{1}{4}$; for a corner, it's $\frac{1}{2}$.)....

Jan 18, 2020 02:33
@Bellatrix Why would that be surprising - after all the comments are displayed to everybody.
Jan 17, 2020 06:16
@Bellatrix But if you suggest that anyone failing to get an answer to their homework question should be able to come here, then I am decidedly against that.
Jan 15, 2020 08:04
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Q: Do side-rational triangles of the same area admit side-rational dissections?

Steven StadnickiCall a polygon side-rational if the lengths of all its sides are rational. Call a dissection of a polygon side-rational if all of the polygons within the dissection are side-rational. Then my question is as in the title: Do any two rational triangles of the same area have a common side-rationa...

Jan 10, 2020 16:19
6
Q: Are these continued fractions of integrals known?

TheSimpliFireMotivated by this paper on polynomial continued fractions (Bowman, 2000), I thought about various extensions to current definitions of these fractions. What if we defined a continued fraction such that the numerator of each fraction is the integral of the previous one? That is, define th...

Jan 9, 2020 06:05
Judging by this feature request I guess that the custom message given for a bounty is lost after the bounty expires: Add notice contents to the timeline.
Jan 9, 2020 06:04
Hmm. Do we need a mechanism for marking a bounty suggestion as being currently sponsored? Anyone can easily find the answer by clicking, but...
Jan 8, 2020 16:04
I'm ready to make it rain you guys. Who shall relieve me of this burdensome new question rep?
Jan 7, 2020 13:11
@hardmath I would say that you can trust your common sense, and use whatever tag you think is prudent. In other words, I like the approach of ask for forgiveness rather than permission :-). If a tag is later found misleading, or a better idea comes up, we can refine the guidelines at that time.
Jan 4, 2020 09:28
Good points @Martin. Glad to hear your suggestions. We could experiment with oneboxing to make pearl suggestions/endorsements stand out from other chat. If it is found too disruptive or space consuming, we can re-evaluate.
Jan 4, 2020 09:22
Also, if the post is oneboxed, users get a preview. And it would also be possible to search among the questions in a specific tag. (As an example, here is such search in the main chatroom.)
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