# Questions tagged [gm.general-mathematics]

Questions about mathematics which don't fall into the other arXiv categories. If you have a general question about mathematics but it is not research level, it's off-topic but it might be welcomed on Mathematics Stack Exchange.

297
questions

20
votes

4
answers

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### Is spherical trigonometry a dead research area?

When I was an undergrad, the field of spherical trigonometry was cited as a once-popular area of math that has since died. Is this true? Are the results from spherical trigonometry relevant for ...

38
votes

12
answers

9k
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### Is amateur research in mathematics viable?

After a long reflection, I've decided I won't go to graduate school and do a thesis, among other things. I personally can't cope with the pressure and uncertainty of an academic job.
I will therefore ...

0
votes

1
answer

59
views

### Computation involving Gauss integer function

I have used mathematica to test following equation is true
\begin{equation}
\sum_{a,b=0}^{m-1} \left[\frac{a+b n}{m}\right] = \frac{n m^2}{2} -\frac{nm}{2}
\end{equation}
where $[x]$ is the floor ...

2
votes

2
answers

536
views

### What is the most "informative" Yes/No math question you know? [closed]

Imagine that alien civilization contacted you and offered to answer one math question. This should be a Yes/No question (so, you cannot ask for a million-digit binary string encoding the answers to a ...

1
vote

0
answers

38
views

### The exact distribution of the conditional distribution of the OLS estimator

This is the problem that I have tried figuring it out for a while, and I still need some advice because there is no explicit derivation in the textbook that I have seen so far. The problem looks easy ...

0
votes

0
answers

99
views

### What is the meaning of PUP in remarks?

I see the remarks in Gowers’s The Princeton Companion to Mathematics. What is the meaning of the abbreviation ‘PUP’? Never seen before…

10
votes

1
answer

277
views

### Can you get any natural number from 4 by performing given operations?

You can perform the following operations on numbers:
divide the number by 2,
add 0 or 4 at the end of the number.
Can you get any natural number from 4 by performing only these operations?
So far I ...

8
votes

6
answers

1k
views

### Surprising applications of the theory of games?

I am currently studying the applications of games in quantum information theory and related fields and I am aware of its uses in places like model theory and set theory. So I was curious, what are ...

0
votes

0
answers

67
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### How to eliminate angle in a Glissette equation of carried point of a line sliding along two lines not at right angles

Glissettes are the curves trances out by a point carried by a curve, which is made to slide between given points or curves. My problem specifically include a line which slides between two fixed lines (...

133
votes

31
answers

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### Conceptual reason why the sign of a permutation is well-defined?

Teaching group theory this semester, I found myself laboring through a proof that the sign of a permutation is a well-defined homomorphism $\operatorname{sgn} : \Sigma_n \to \Sigma_2$. An insightful ...

9
votes

1
answer

488
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### How far away can we get by multiple rounding and unit change?

This question is inspired by xkcd #2585 (Rounding):
Let $u_0,\ldots,u_n$ be positive real numbers (we can assume w.l.o.g. that $u_0=1$) or “units”.
Consider the following directed graph: its vertices ...

0
votes

0
answers

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### How can C2 double-helices, produce C3 rotational symmetry?

I am trying to solve the structure of a helical protein complex using a software for maximum a posteriori refinement of (multiple) 3D reconstructions (Relion).
When searching for helical symmetry, the ...

2
votes

1
answer

99
views

### Algorithm for compact polynomial expressions

Sometimes an ugly polynomial (perhaps in several variables) can be expressed as a small sum of much simpler polynomials. Can this be done algorithmically? More precisely:
Is there a reasonable
...

3
votes

0
answers

218
views

### Récoltes et Semailles for the non (algebraic-) geometer

With the recent publication of Grothendieck's Récoltes et Semailles, I've been umm-ing and ah-ing about whether to get a copy, if only for the "soaking nuts" story. My French reading is ...

10
votes

3
answers

801
views

### Progress in robustifying mathematics - i.e. making mathematical theorems robust to small changes in hypotheses

The idea of making a mathematical theorem robust to small changes in its hypotheses has been known for some time. In areas such as group theory reasonable progress has been made leading to the theory ...

12
votes

4
answers

663
views

### What are some examples of understanding a space by studying the functions on this space?

In Quantum theory, groups and representations, Peter Woit writes:
A fundamental principle of modern mathematics is that the way to
understand a space $M$, given as some set of points, is to look at $...

5
votes

1
answer

258
views

### How the solve the equation $\frac{(a+b\ln(x))^2}{x}=c$ [closed]

I need to solve the equation
$$\frac{(a+b\ln(x))^2}{x}=c$$
where $a$, $b$, and $c$ are given. It is known that $a$ and $b$ are fixed and satisfy some condition such that the left hand side is ...

1
vote

0
answers

72
views

### Drawing a 3D object in a 3D environment, and converting to math [closed]

So I have been granted a free time and I want to work on a project but first I had to research.
As we know, lines have infinite points, and with lines, we can create infinite shapes. I want to let ...

3
votes

0
answers

232
views

### What does it mean to solve an equation?

Assume that we want to find all integer (or rational) solutions to the polynomial Diophantine equation
$$
P(x_1,\dots,x_n) = 0
$$
where $P$ is a polynomial with integer coefficients. Do we have a ...

6
votes

0
answers

214
views

### Mathematical questions or areas amenable to AI [duplicate]

This question regards the new paper "Advancing mathematics by guiding human intuition with AI" by Davies et al. (Nature, 2021) (DOI link in open access) in which researchers at Deepmind ...

12
votes

2
answers

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### Is it ever unnecessary to mathematically formalize a concept?

From my understanding, mathematics sometimes gives rise to new physical/tangible laws and the converse is also true. In particular, physical phenomena give rise to new mathematics.
In all of the cases ...

31
votes

2
answers

907
views

### Math videos containing real time rough thinking

I find this vlog experiment of Gowers very brave, and I think his idea of having examples of real-time mathematical thinking by experts can be very encouraging for young mathematicians, who imagine ...

41
votes

18
answers

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### Results in linear algebra that depend on the choice of field

Linear algebra as we learn it as undergraduates usually holds for any field (even though we usually learn it for the complex, or real, numbers).
I am looking for a list of concepts, and results, in ...

1
vote

0
answers

103
views

### Closed form for $\sum _{k=1} ^n \frac k 2 \,\operatorname{sgn} \left( \frac 1 {k^2} + \cos \frac {2\pi n} k-1 \right)$ [closed]

I am looking for the closed form of
$$\sum _{k=1} ^n \frac k 2 \,\operatorname{sgn} \left( \frac 1 {k^2} + \cos \frac {2\pi n} k-1 \right) \ .$$
Wolfram Alpha cannot do this for me, so I am forced to ...

4
votes

2
answers

395
views

### Theorems with finite sets of exceptions

Exceptions are interesting. Sometimes, they're also important. If a theorem with exceptions is important for a subject, there are liable to be many corollaries of the form "either this is true... ...

55
votes

23
answers

7k
views

### Golden ratio in contemporary mathematics

A (non-mathematical) friend recently asked me the following question:
Does the golden ratio play any role in contemporary mathematics?
I immediately replied that I never come across any mention of ...

11
votes

3
answers

529
views

### Any hints on how to prove that the function $\lvert\alpha\;\sin(A)+\sin(A+B)\rvert - \lvert\sin(B)\rvert$ is negative over the half of the total area?

I have this inequality with $0<A,B<\pi$ and a real $\lvert\alpha\rvert<1$:
$$ f(A,B):=\bigl|\alpha\;\sin(A)+\sin(A+B)\bigr| - \bigl| \sin(B)\bigr| < 0$$
Numerically, I see that ...

36
votes

22
answers

6k
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### Theorems with many distinct proofs

I was told that whenever one learns a new technique, it is a good idea to see if one can prove a well-known theorem using the new technique as an exercise. I am hoping to build a list of such theorems ...

62
votes

20
answers

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### Situations where “naturally occurring” mathematical objects behave very differently from “typical” ones

I am looking for examples of the following situation in mathematics:
every object of type $X$ encountered in the mathematical literature, except when specifically attempting to construct ...

18
votes

3
answers

2k
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### Heat map of current mathematics

The recent article on Quanta
(by Natalie Wolchover)
concerning $\aleph_1$ vs. $\aleph_2$ suggests that there is
excitement within that community:
Juliette Kennedy: "It’s one of the most ...

20
votes

2
answers

1k
views

### sci.math.research archive?

Does there exist an archive somewhere of posts to the USENET newsgroup sci.math.research?
The best approximation I'm aware of is Google Groups. However, despite ...

51
votes

10
answers

6k
views

### Changes forced by the pandemic

The Covid-19 pandemic has changed our work-lives in ways few of us could have anticipated. These exceptional circumstances have forced each one of us and each one of our institutions to adapt, ...

0
votes

1
answer

130
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### What are examples of mathematical objects that are 'constructed out of' a range of other objects but fall out of them? [closed]

What are examples of mathematical objects that are somehow 'constructed out of' a whole range of other objects but fall out of them? One example that comes to my mind is that of ordinal numbers: $\...

33
votes

14
answers

6k
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### Is pure mathematics useful outside of mathematics itself? [closed]

From time to time Mathoverflow allows soft questions because they are arguably best answered by active mathematicians and they can benefit other mathematicians/PhD students/math undergraduates. I ...

5
votes

0
answers

196
views

### Is my equation for finding the length of a curve correct?

My son has been working on equations for finding length of the length of a curve without any resources (computers, calculators...) while in prison. He is wondering if he is on the right path. Sadly my ...

1
vote

2
answers

193
views

### The sum of triangular functions

I have a sum of $N-1$ triangular functions to calculate and it is $$s = \sum_{q=0}^{N-1} \frac{W_q \left(\cos\left(\dfrac{n\pi q}{N}\right) + \cos\left(\dfrac{(n-1)\pi q}{N}\right)\right) }{ 1 + \cos\...

2
votes

1
answer

913
views

### Examples of reputable journals in mathematics without impact factor? And is it good to publish in them?

I came across a journal which is reputable in terms of not being listed in Beall's list, but which according to scimagojr and clarivate does not have an impact factor. The journal is Journal of ...

4
votes

0
answers

102
views

### What do you call such a relation between subsets in a poset

Consider a poset $(X, \geq)$. Let's define a new relation $\succsim$ on subsets of $X$: for $A, B\subseteq X$, say $A\succsim B$ if for any $a\in A$ and any $b\in B$, we have $a\geq b$.
Does such a ...

74
votes

10
answers

9k
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### What are possible applications of deep learning to research mathematics?

With no doubt everyone here has heard of deep learning, even if they don't know what it is or what it is good for. I myself am a former mathematician turned data scientist who is quite interested in ...

7
votes

0
answers

183
views

### Fraction of elements in $\mathbb{Z}_n$ satisfying a certain equation

From a question arising in Game Theory, I want to calculate the sequence
$$
a_n =
\max_{f_A, f_B : \mathbb{Z}_n \to \mathbb{Z}_n}
\frac{\#
\left\{
(x,y) | f_A(x) - f_B(y) = xy \mod n
\right\}}{n^2}
$$...

5
votes

1
answer

238
views

### Get the commands history from GAP system

I am not sure whether this was asked before, but I didn't find a reference in GAP system documentation on how to print the history of the command line (Ubuntu installation).
For instance:
...

1
vote

1
answer

260
views

### Can the solutions to this beautiful equation always be expressed in terms of algebraic numbers?

For $n\geq1$, the largest solution to this lovely equation is a local extremum on a function related to the Fibonacci sequence:
$$\sum_{k=1}^{n} k{(-1)^{k}} \cdot \frac{\sin(\frac{k\pi}{x} )}{3+2\cos(\...

3
votes

6
answers

439
views

### how to prove this high degree inequality

Let $x$,$y$,$z$ be positive real numbers which satisfy $xyz=1$. Prove that:
$(x^{10}+y^{10}+z^{10})^2 \geq 3(x^{13}+y^{13}+z^{13})$.
And there is a similar question: Let $x$,$y$,$z$ be positive real ...

0
votes

2
answers

94
views

### Existence of functions satisfying a homogeneity condition

Do there exist a (non-trivial) globally Lipschitz continuous function $g:\mathbf{R}\to\mathbf{R}$ and a non-decreasing function $f:\mathbf{R}_+\to\mathbf{R}_+$ such that the identity
\begin{equation}
...

5
votes

1
answer

269
views

### Is the solution to this trig function known to be algebraic or transcendental?

This largest solution to this gorgeous equation is the first local extremum on a function related to the Fibonacci sequence:
$$x^2 \cdot \sin \left(\frac{2\pi}{x+1} \right) \cdot \left(3+2 \cos \left(\...

3
votes

0
answers

150
views

### Does this trig equation have a closed-form solution?

This equation came up when I was looking at the Fibonacci sequence; I adore its symmetry:
$$x^2 \cdot \sin \left(\frac{2\pi}{x-1} \right) \cdot \left(3+2 \cos \left(\frac{2\pi}{x} \right) \right) = (x-...

3
votes

1
answer

124
views

### What is the ideal form of an h-curve?

This question concerns mathematical modelling of the citation curve, well-known in the sciencemetry.
The citation curve (or else the $h$-curve) of an individual researcher is the vector $(c_1,c_2,\...

2
votes

0
answers

82
views

### Good notation for finite partial functions from $\omega$ to 2

I'm working in computability theory and need to use partial functions with finite domain from $\omega$ to 2 as approximations in my current paper. Normally this is simply done using $2^{< \omega}$ ...

0
votes

0
answers

111
views

### Formula from a form having one dirac delta to a form having two dirac delta

I'd like to ask at which condition I can transform a formula with one delta function to a form with two delta function.
Suppose a physical system has a quasi-continuous energy-level spectrum $E_1$, $...

44
votes

4
answers

4k
views

### How to invoke constants badly

In a nice and witty lecture titled "how to write mathematics badly" (available on YouTube at https://www.youtube.com/watch?v=ECQyFzzBHlo&t=23s), Jean-Pierre Serre describes various ways ...