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Questions tagged [symmetry]

Questions about symmetry, in group theory, geometry or elsewhere in mathematics. See https://en.wikipedia.org/wiki/Symmetry

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What function symmetric and has unique solution?

I have multiple operands, say a, b, and c. I want an operator acting on a, b, and c, but the result should be invariant of order of operands (symmetric), and there should be no other pair with same ...
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1answer
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Is this shape a fair D-24?

I've been looking at polyhedra, incuding Platonic solids as well as Archimedean and Catalan solids. Catalan solids are face-transitive, which I believe implies that they are "fair dice", in the sense ...
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Wassertein and symmetry

So here's a scenario: I have points $(\mu_1^j,\mu_2^j)$ and I associated them the following distribution $$\rho_j=1/2\delta_{\mu_1^j}+1/2\delta_{\mu_2^j}$$ These have symmetry (exchanging $\mu_1^j$ ...
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Symmetry relative to the straight line. [closed]

Write the equation of symmetry relative to the line y = 2x + 1 with a slip by vector [2, -1]. I do not know how to start this task.
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symmetry of partial differential equations (Heat equation)

Morning everyone, I am doing some problem sheets for my class in Partial differential equations where we dont have an actual textbook. we are given a pack on notes. I am having an issue discerning ...
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Reason: non-integer powers of Hermitian matrix not Hermitian?

Let $\alpha = 2.1$. If $A$ is symmetric real, $A^\alpha$ remains symmetric (although it could be complex-valued). If $B$ is Hermitian, $B^\alpha$ isn't Hermitian (losses the symmetry). However, for ...
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Is there a general theory of when certain polynomials are integrable due to symmetry tricks?

Consider the functions $x^2$ and $x^4 + 2x^2y^2$ on the unit sphere $S^2$. The surface integral of these functions over the sphere can easily be calculated by symmetry via $$3 \iint_{S^2} x^2 \mathrm{...
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Proof that there exist only 17 Wallpaper Groups (Tilings of the plane)

I had a professor who once introduced us to Wallpaper Groups. There are many references that exist to understand what they are (example Wiki, Wallpaper group). The punchline is $$There \,\, are \,...
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Making the condition homogeneous

I saw it on AoPS, very great: https://artofproblemsolving.com/community/c6h1274759p6726915 JunBo-Yang used his own substitution for the condition: $a^{\,2}+ b^{\,2}+ c^{\,2}+ 3\,abc= 6$ , then: $$a= \...
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example of an “almost-metric” without symmetry

It is not difficult to find an "almost-metric" $d$ that satisfies all axioms of a metric except the triangle inequality. It should also be possible to construct a function $d$ that satisfies all ...
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What can I say about the form of an invariant function?

I have a general scalar function which has the properties: \begin{align} f(s\,a,b,c)&=s\,f(a,b,c)\\ f(s\,a,s\,b,s\,c)&=f(a,b,c) \end{align} where $s$ can be any real number, so the invariance ...
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Does the action of a linear map on $k$-dimensional subspaces determine it up to scaling?

Let $V$ be a real $d$-dimensional vector space, and let $1 \le k \le d-1$ be a fixed integer. Let $A,B \in \text{Hom}(V,V)$, and suppose that $AW=BW$ for every $k$-dimensional subspace $W \le V$. Is ...
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What does “super-integrable” mean?

What does "super-integrable" mean? Example from here (p. 2): …the Coulomb problem is super-integrable. Namely, it is not just rotation invariant, but as well admits further integrals given by ...
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Symmetricity of binomial distribution

For each random variable, $X$, define: $Sym_X(c) = \frac{\Pr[X \geq \mu_X + c]}{\Pr[X \leq \mu_X - c]}$. I use this definition to measure how symmetric the distribution is. Let $X$ be a binomial ...
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Stuck on a Geometry Problem

$ABCD$ is a square, $E$ is a midpoint of side $BC$, points $F$ and $G$ are on the diagonal $AC$ so that $|AF|=3\ \text{cm}$, $|GC|=4\ \text{cm}$ and $\angle{FEG}=45 ^{\circ}$. Determine the length of ...
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Prove that $S_3/C_3$ is a (quotient) group

Consider $S_3$ to be the symmetries of a triangle, and let $C_3$ be a subgroup that cycles the three corners, so generated by: $(1 \ 2 \ 3 )$. Using Lagrange's theorem, compute $k = |S_3/C_3|$. ...
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commutativity of rotations and reflections

The question is as follows: [Concerning the square embedded in the plane,] prove that the $90^{\circ}$ clockwise rotation $\sigma$ and the reflection through the north/south axis $\rho$ do not ...
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How to take the determinant of a rank(1,1) tensor?

I want to find the Jacobian matrix and its determinant of the generic infinitesimal transformation: $x'^\mu=x^\mu+\epsilon_\alpha\frac{\delta x^\mu}{\delta \epsilon_\alpha}$ where $\epsilon_\alpha$ ...
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1answer
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How is this cube symmetric?

I am having a hard time with this, but I am reading in a published journal that this cube is symmetric when distributing +1 and -1 in the following corresponding points. Positions 1-12: $$[+,+,+,-,-,+...
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Where is it used that the symmetry conserves the symplectic form in noether's theorem.

For the proof of Noether's theorem, it seems like that the only thing that's important for the symmetry map $S_g : M \to M$ is that it conserves the Hamiltonian (which will then imply that the moment ...
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What is symmetry in physics in the mathematical sense, using (Lie) groups

In physics, we sometimes say that, for example, a certain classical system has a certain symmetry, which is given by some group. I don't feel like I understand this well enough. Are there some good ...
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1answer
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Properties of a step function

Consider the step function $\Delta: \mathbb{R}\rightarrow [0,1]$ $$ \Delta(x;\lambda,\mu)\equiv \sum_{j=1}^J \lambda_j\times 1\{\mu_j\leq x\} $$ where $\lambda\equiv (\lambda_1,...,\lambda_J)$ is a ...
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Flux through sphere symmetry?

Is the flux through a sphere centered at the origin of the vector field $\boldsymbol{F} = (-x,1,z)$ equal to $0$? If so, is there any simple symmetry which suggests it? I have done the calculation ...
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When does $P\text{SO}P^{-1} \subseteq \text{SO}$?

Let $P \in \text{GL}_n^{+}(\mathbb {R})$. Suppose that $P\cdot \text{SO}(n)\cdot P^{-1} \subseteq \text{SO}(n)$. Is it true that $P \in \lambda \text{SO}(n)$ for some $\lambda \in \mathbb{R}$? I ...
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Archimedean spiral - symmetry test

It is usually stated in Precalculus textbooks that in polar coordinates when a relation between $r$ and $\theta$ passes a symmetry test then the curve described by that relation has that symmetry. ...
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Representation theory and symmetry in physical systems.

I've come multiple times across statements like these Representation theory remains the method of choice for simplifying the physical analysis of systems possessing (a high degree of) symmetry ...
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Symmetry of a planar system and product of inertia

I read the following sentence here: "The products of inertia occupy the off-diagonal positions and measure the asymmetry of the mass distribution with respect to the planes of the inertia frame of ...
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1answer
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Proving symmetry and transitivity of a relation

Let R be the relation {(1,1),(1,2),(2,2),(1,3),(3,3)} on the set {1,2,3}. I am having difficulty proving that it is symmetrical and transitive. I know for symmetry we have to prove if xRy then yRx (...
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Divisibility of kissing numbers

Denote by $ K(d) $ the kissing number in dimension $ d $. I have two questions : 1) does $ d\mid K(d) $ for all $ d $? 2) does $ d\mid D $ imply $K(d)\mid K(D) $?
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Symmetric relation and definition of even numbers

Let a relation $\rho$ be defined on $\mathcal{Z}$(set of integers) by '$a \rho b$ if and only if $a-b$ is even' for $ a,b \in \mathcal{Z}$. Then, is the above relation symmetric or anti-symmetric? ...
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Does having two lines of symmetry $y=0$ and $y=-x$ imply that the shape also has lines of symmetry $x=0$ and $y=x$

I have been wondering if a shape/curve that has a line of symmetry along the lines $y=0$ and $y=-x$ is guaranteed to also have lines of symmetry along the lines $x=0$ and $y=x$. My gut feeling tells ...
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prove that a conjugate of a glide reflection is a glide reflection

This question has an answer elsewhere, a conjugate of a glide reflection by any isometry of the plane is again a glide reflection, but they use results which were not mentioned in the book. The ...
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Is there a theory of “almost symmetry” generalizing group theory?

Apologies for the inescapably soft question. Does there exist a theory that aims to develop tools analogous to those of group theory, except for the study of objects that are merely almost ...
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1answer
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Discrete Spherical Symmetry Group

Take two spheres each having a certain number (say 5) of identical dots on them. What is the approach to proving/disproving that they are equivalent under the set of spherical rotations? One could ...
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1answer
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In which degrees there exist non-decomposable elements in the exterior algebra?

I am trying to get a better understanding of the concept "decomposable" element in an exterior algebra. Let $V$ be a $d$-dimensional real vector space, and let $1<k<d$. For which tuples $(k,d)$,...
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A characterization of the subgroup of $\text{GL}(\bigwedge^k V)$ which preserves pure tensors?

Let $V$ be a $d$-dimensional real vector space, and let $1<k<d$. Set $$H=\{B\in\text{GL}(\bigwedge^k V) \, | \, B \,\text{ preserves pure tensors }\}$$ (i.e. $B \in H$ if it maps ...
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Orbit of a point and symmetries of a specific graph

Given is the graph: I am interested in determining the orbit of the point 1 and also to determine the amount of symmetries that fix each of the points 1, 2 and 3? My approach: Notice that the ...
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1answer
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Total number of ways to paint the faces of a regular icosahedron with $20$ distinct colors

If all the 20 faces of a regular icosahedron are painted with a set of 20 distinct colours then the total number of such icosahera possible. The cube analogue of this is more well known and the answer ...
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1answer
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Inverting variable size block matrix

Given a block matrix $M$ $$\bf M=\left(\begin{array}{cccc} a\ \mathbb{I}_{2} & \boldsymbol{\boldsymbol{A}}_{12} & \boldsymbol{A}_{13} & \boldsymbol{0_{(2,3)}}\\ \\ \boldsymbol{A_{21}} &...
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Line of Symmetry of the Zeta Function

I heard once that 0.5 is the line of symmetry of the Riemann Zeta Function. What does that mean? A graph illustrating would be helpful.
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Does Young's inequality hold only for conjugate exponents?

Suppose that $ab \leq \frac{1}{p}a^p+\frac{1}{q}b^q$ holds for every real numbers $a,b\ge 0$. (where $p,q>0$ are some fixed numbers). Is it true that $ \frac{1}{p}+\frac{1}{q}=1$? I guess so, and ...
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A woman planning her family considers the following schemes on the assumption that boys and girls are equally likely at each delivery

A woman planning her family considers the following schemes on the assumption that boys and girls are equally likely at each delivery: (a) Have three children. (b) Bear children until the first girl ...
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Expressing musical patterns as a mathematical model?

My goal here is to compare visual symmetry and express the temporal symmetry of music in a similar visual manner. I'm not very well versed at math and hence I'm not sure how to go about this. ...
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Classify the regular polygons that fit about a common vetex

I know this can be solved using a (quasi-)symmetric groups approach from crystallography, but I wish to solve it with a more simple approach, number theory motivated. I wish to classify the regular ...
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When studying the dihedral group of a square, do we consider only vertices or the whole points which the square covers?

When studying the dihedral group of a square, do we consider only vertices or the whole points which the square covers? Because the vertices of square also gives the same symmetries.
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Location shifted symmetric probability distributions

Let $G: \mathbb{R}\rightarrow [0,1]$ be a cumulative distribution function (CDF) symmetric about zero, i.e., $G(x)=1-G(-x)$ at each $x\in \mathbb{R}$. Take some real numbers $\mu_1,\mu_2$. Consider ...
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Compare classical and modified algorithm of Cholesky

Let $\textbf{A}$ be a symmetric matrix with tthe modified Cholesky factorization $\textbf{A} = \textbf{R}^T\textbf{D}\textbf{R}$ and the classical factorization $\textbf{A} = \textbf{R}_c^T\textbf{R}...
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Constrained Optimization Insights

I have been experimenting with the following problem paraphrased from Khan Academy: A manufacturer's revenue is $100h^{2/3}s^{1/3}$, where $h$ is the number of hours of labor hired, and $s$ is the ...
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Which matrices commute with $\operatorname{SO}_n$?

$\newcommand{\GLp}{\operatorname{GL}_n^+}$ $\newcommand{\SO}{\operatorname{SO}_n}$ Let $n>2$, and Let $A \in \GLp$ be an invertible real $n \times n$ matrix, which commutes with $\SO$. Is it true ...
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How can we show that $I_{yy}=I_{zz}=I_{xx}$ and $I_{xy}=0$ using symmetry arguments?

Consider two integrals of the form $$I_{xx}=\int x^2 f(r)d^3r,~~I^\prime=\int xy ~f(r)d^3r$$ where $f(r)$ is a function of $r=|\vec{r}|$ only and has no dependence on $\theta,\phi$ in pherical polar ...