Questions tagged [algebraic-combinatorics]
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91
questions with no upvoted or accepted answers
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views
Subalgebras of a polynomial ring carved out by (families of) coefficient equalities
Let $\mathbf{k}$ be a field, and let $P=\mathbf{k}\left[ x_{1},x_{2}
,\ldots,x_{n}\right] $ be a polynomial ring over $\mathbf{k}$ in $n$
variables $x_{1},x_{2},\ldots,x_{n}$. Alternatively, $P$ can ...
3
votes
0
answers
124
views
Number of adjoint orbits containing a $(0,1)$-matrix
Motivated by this
question, what can be said about the number $f(n)$ of adjoint
orbits of $\mathrm{Mat}(n,\mathbb{C})$ (the ring of all $n\times n$
complex matrices) that contain a $(0,1)$-matrix? ...
3
votes
0
answers
108
views
Decomposition of Schur modules over the orthogonal group
Let $V=\mathbb{R}^n$ and $O(n)$ the orthogonal group acting with its standard action on $V$. Now for any partition $\lambda$ we have the Schur module $S_\lambda V$ which is a representation of $O(n)$. ...
3
votes
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119
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Shifted schur function and holonomic
Now let us denote by $\Lambda^{*}(n)$ the algebra of polynomials in $x_{1},\ldots,x_{n}$ that become symmetric in new variables
$$ x_{i}'=x_{i}-i+c, \ i \in 1,\ldots,n.$$
Here c is a arbitrary fixed ...
3
votes
0
answers
696
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Puzzle in 3D grid with black and white boxes, related to shelling
Consider a $n$ by $n$ by $n$ grid represented by the set of $3$-uples $S=\{1,2,\dots, n\}^3$.
A line (resp. slice) of $S$ is a subset of cardinal $n$ (resp. $n^2$) where two components (resp. one ...
3
votes
0
answers
685
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Union of the conjugates of maximal subgroups
This post is a generalization of Union of the conjugates of a proper subgroup.
Consider an interval $[H,G]$ in the subgroup lattice of the finite group $G$, with $H \neq G$ and such that:
(1) $ \...
3
votes
0
answers
206
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Hook-content polynomial
Let $\lambda$ denote the hook of size $d$ for a fixed integer $d>0$. For $d=2$ there are two kinds of hooks for $d=3$ there are 3 different kind and so on. $c(\Box)$ denote the content of the $\...
3
votes
0
answers
115
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Dimension of the sum of images of transpose
$\newcommand{\rank}{\operatorname{rank}}\newcommand{\im}{\operatorname{im}}$
Given $A,B\in M_{n\times n}(k)$, define $\rank(A,B):=\dim(\im A+\im B)$. I'm looking for results regarding relationships ...
3
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386
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Software for Combinatorial Algebra sought
I am looking for software which helps me do straightforward tasks in combinatorial algebra. Let me give an example of what I mean by a straightforward task:
I have two graded (generally ...
2
votes
0
answers
197
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Geometric or combinatorial interpretations of the (weak) Bruhat order?
$\DeclareMathOperator\Inv{Inv}$The weak Bruhat order on the symmetric group has a straightforward combinatorial interpretation: Consider a set of labelled balls $1,2,\dotsc,n$. Then for two ...
2
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90
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Double Schur function expansion
In literature, I have seen the weighted Hurwitz number $N_{g,n}(d_1 , d_2 \ldots , d_n)$ which are symmetric number and they can be written as double Schur function expansion.
\begin{align} \label{eq:...
2
votes
0
answers
66
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Annihilator of the of the generating function not holonomic
The following is a generating function in $x,h$ with infinite parameters
$q_1,q_2\ldots,$ and $w_1, w_2,\ldots$.
$$\Psi(x, h)= \sum_{d=0}^{\infty} s_{(d)} (q_1, q_2, \ldots) \exp \bigg( \sum_{r=1}^{\...
2
votes
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answers
95
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Diagonal operator and infinite wedge space formalism
Let $\bigwedge^{\infty /2}V$ denote semiinfinte wedge space. The followin article section 2 gives a good description about the space and the operator on it.
https://arxiv.org/pdf/math/0207233.pdf
...
2
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0
answers
111
views
Holonomic modules and Holonomic functions
Let
$$f_{d}(h):=\sum_{k=1}^{d}(-1)^k\binom{d-1}{k-1}\prod_{i=1}^{d}G((i-k)h) . $$
I have proved that $ F(x):=\sum_{d=1}f_{d}\frac{x^{d}}{d!}\in \mathbb{C}(h)[[x]]$ is holonomic and arrive at a ...
2
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0
answers
88
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Rank-unimodality and Sperner property of higher dimensional partitions
I did a google-search but have not been able to find much reference on this problem. So I am asking it here hoping to get some information.
Consider the set of all 4-dimensional Ferrer's diagram ...
2
votes
0
answers
273
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An (open?) problem about a sequence of nested principal sub-matrices and their determinants
Problem: Let $A$ be a $n \times n$ integer matrix, $\det(A) = \pm 1$. Under which conditions there exist a nested sequence of principal submatrices of size $n$ such that they all have determinant $\pm ...
2
votes
0
answers
102
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Lagrangean equations for the generating function of quadrangulations
Let $M(z)$ be the generating function of edge-rooted connected quadrangulations, with $z$ marking the number of edges. I derived the following Lagrangean equations for $M(z)$:
$$M(z) = \psi(L(z)),~\...
1
vote
0
answers
110
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A combinatoric identity for characters of reductive groups
Let $G$ be a reductive group over an algebraic closed field (of char 0 if necessary). Let $T\subset G$ be a maximal torus and $S=\mathrm{Sym}^*(X(T))$ be the symmetric algebra of characters of $T$. ...
1
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135
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References/applications/context for certain polytopes
First, let's consider an almost trivial notion. With any subspace $V\subset \mathbb R^n$ we associate a convex polytope $P(V)\subset V^*$ as follows. Each of the $n$ coordinates in $\mathbb R^n$ is a ...
1
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0
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86
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Making the entries of a matrix positive
I am considering two slightly more relaxed version of the question asked here: https://math.stackexchange.com/questions/119034/making-the-entries-of-a-matrix-positive
The two questions are:
Question 1:...
1
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0
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177
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Combinatorial bijection on monotone sequences
Let $(n),\mu$ be the partition of $n$ define $H_g^{m}((n);\mu)$ count's the number of tuples $(\tau_1,\ldots,\tau_r)$ of transposition in symmetric group $S_n$ with the following conditions
$$ (1,2,\...
1
vote
0
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88
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Flag $f$-vectors of CW-complexes
Hidden away in the appendix of this nice paper by Björner and Kalai, they give a clean description of $f$-vectors that can arise from regular CW-complexes in terms of truncations of the Euler-Poincaré ...
1
vote
0
answers
99
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About parabolic Kazhdan-Lusztig polynomials
Denote by $P^{I,y}_{x,w}$ be the parabolic Kazhdan-Lusztig polynomial of ${}^IW$ of type $y$.
I have heard that the polynomials $P^{I,q}_{x,w}$ give the transition matrix between a canonical basis ...
1
vote
0
answers
29
views
Extension of definition of Holonomic closure
My question is about finding the annihilator of a series. Let me begin with what is known and then ask my question. Let $s_d(\frac{q_1}{h},\ldots )$ denote schur function for partition $\lambda =[d]$ ...
1
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0
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122
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An alternative proof of a subgroup lattice characterization of the infinite cyclic group
In Schmidt's book Subgroup lattices of groups, Theorem 1.2.5 states that a group $G$ is cyclic if and only if its subgroup lattice $L(G)$ is distributive and satisfies the maximal condition. Its proof ...
1
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0
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281
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On the number of Eulerian orderings
This post is a sequel of Eulerian ordering of the integers modulo n.
Let us recall the definition of an Eulerian ordering:
Let $n>1$ be an integer. Consider the set $C_n := \{0,1, \dots , n-1\}$....
1
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41
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Counting arrangements around a table with constraints
I have $n$ guests seated around a circular table. I want to serve them meals so that given any two guests $u$ and $v$, either
i. $u$ and $v$ have different meals, or
ii. $u$'s two neighbors have a ...
1
vote
0
answers
174
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Holonomic generating function
Let $\lambda$ denote a hook of size $d$ and $c(\Box)$ the content of $ \Box \in \lambda $. Let $ \text{Hooks}(d) $ be the set of hooks with $d$ boxes. Define
\begin{align}
B(d)&=
\frac{1}{d!h^{d-1}...
1
vote
0
answers
109
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Hook-content polynomial 2
Recently I have proven the following identity
\begin{align}
\sum_{\lambda\in \text{different hook of size d}} \frac{1}{d!} (-1)^{ht(\lambda)-1} \, \dim \lambda \, \prod_{\Box \in \lambda} \frac{1}{1-...
1
vote
0
answers
95
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combinatorial ergodicity and promotion
According to J. Propp, T. Roby, and (I believe) others, a cyclic action on a finite set $S$ given by a bijection $\zeta: S \longrightarrow S$ is said to be ${\it ergodic}$ with respect to a statistic ...
1
vote
0
answers
223
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Does $[H_i , G_i]$ distributive imply $[H_1 \times H_2, G_1 \times G_2]$ modular?
Let $L(G)$ be the subgroup lattice of $G$ and $[H, G]$ an interval in $L(G)$.
A lattice $(L, \wedge, \vee)$ is distributive if $a∨(b∧c) = (a∨b) ∧ (a∨c)$, $\forall a,b,c \in L $, and is modular if ...
1
vote
0
answers
309
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Rank generating functions on a graded poset and a linear extension of it
Let $A$ be a possibly infinite ensemble and let $\leq$ be a partial order between elements of $A$. We denote $P_{\leq}=(A,\leq)$ the corresponding poset. Furthermore, we suppose that $P$ is graded, i....
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0
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71
views
Gessel-Viennot theorem
In the paper, page 76, why we need the condition that the subpath lying between lines y=-x and y=k+1 consists entirely of vertical steps?
0
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0
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285
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Relation between $3$-term Plücker relations and more than $3$-term Plücker relations
$\DeclareMathOperator\Gr{Gr}$Let $\Gr(k,n)$ be the Grassmannian variety of $k$-planes in an $n$-dimensional vector space. The coordinate algebra $\mathbb{C}[\Gr(k,n)]$ is generated by Plücker ...
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88
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Addition theorem for Schur function in multivariable
Working with the following problem Expansion in Schur function of negative binomial exponent
I need to find the expansion of
$$ s_{\lambda}(x_1 + y , x_2 +y, \ldots, x_n +y)$$
in terms of schur ...
0
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0
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71
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Algebraic ode of exponential generating series
Let $G(z)$ be a rational function. So if we have a series
$$S(x):=\sum_{n}a_n x^n $$ where
$$ a_n = \prod_{i=1}^{n}G((i-1)h) $$
We can conclude that the series satisfies a Linear differential ...
0
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0
answers
137
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How to classify rings by combinatorial structures?
There are many ways to encode information about algebraic structures such as groups, rings, etc... in combinatorial form. For example the Cayley graph of a group with a subset of generators, or the ...
0
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78
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Minimizing coefficients in a product related to the Rogers Ramanujan identity
Start with the product for partitions into parts congruent to $1$ or $4$ modulo $5$:
$(1 + x + x^2 + x^3 + ...)(1 + x^4 + x^8 + x^{12} +...)(1 + x^6 + x^{12} + x^{18} +...)$...
Now replace some of the ...
0
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189
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What breaks down in the theory of affine hyperplane arrangments?
It appears to me that there is a substantial amount of combinatorial algebra and geometry supporting the theory of central hyperplane arrangements (See Topics in Hyperplane Arrangements, Aguiar and ...
0
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148
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Methods to get Holonomic functions
Let $a_n$ be a holonomic sequence. By definition, that means there exists a linear differential equation of finite order which annihilates $F(x)$, where
$F(x):=\sum a_n x^n$.
Similarly let $b_n$, $...
0
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146
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Abelian centralizer groups (CA-groups)
I am searching for all information about CA-groups [abelian centralizer groups] and i just found a German book [Huppert] and Nilpotent Centralizer group of Suzuki in 44 pages and Group theory book of ...