Questions tagged [grassmannians]
Grassmannians are algebraic varieties whose points corresponds to vector subspaces of a fixed dimension in a fixed vector space.
255 questions
1
vote
0
answers
25
views
Computing truncation functors associated to admissible subcategories
Let $\mathcal{T}$ be a triangulated category, and let $\mathcal{S} \subseteq \mathcal{T}$ be an admissible subcategory. Recall, this means that the inclusion $\mathcal{S} \hookrightarrow \mathcal{T}$ ...
- 137
2
votes
0
answers
48
views
Do Grassmannians classify numerable vector bundles over arbitrary spaces
The functor $k_{U(d)}$ of the set of isomorphism classes of numerable principal $U(d)$-bundles is represented by $BU(d)$ the Milnor construction of the classifying space. The restriction of $k_{U(d)}$ ...
- 121
4
votes
0
answers
132
views
Is this family of varieties "well known"?
In my research, one can find as a special case the following family of varieties. Fix integers $0<k<n$ and let $G=Gr(k,n)$ be the Grassmannian of $k$-planes in an $n$-dimensional vector space $V$...
- 495
5
votes
0
answers
86
views
Spherical functions in the space of functions on real Grassmannians
Let $G=O(n)$ be the orthogonal group. Let $K=S(O(k)\times O(n-k))$ be the subgroup of $O(n)$.
Then the pair $(G,K)$ is symmetric, and the homomogeneous space $G/K$ is the Grassmannian of $k$-...
- 21.8k
2
votes
0
answers
108
views
Grassmannian containing tangent variety of a curve
We work over $k=\mathbb{C}$. We consider the
the Grassmanian $G(2,4)$ of lines in $\mathbb P^3$ which we embed
by Plücker into $\mathbb P^5$. It is basic that under this embedding
$G(2,4)$ is ...
- 619
4
votes
1
answer
171
views
Representations of $\mathrm{GL}_n(\mathcal{O})$ in functions on Grassmannians
$\DeclareMathOperator\GL{GL}\DeclareMathOperator\Gr{Gr}$Let $\mathbb{F}$ be a non-Archimedean local field. Let $\mathcal{O}$ be its ring of integers.
The natural representation of the group $\GL_n(\...
- 21.8k
4
votes
1
answer
228
views
Permutation of a mixture of (anti)commuting variables and consistency issue regarding the sign
I asked a similar question in PhysicsSE but it seems more like a mathematical issue, so I post here in a more refined form.
I am not confident if the below description of the problem makes sense. ...
- 3,487
1
vote
0
answers
75
views
Trace map for universal bundle of Grassmannian
Let $G := G(k,V)$ denote the Grassmannian of $k$-linear subspaces in a $\mathbb{C}$-vector space $V$ of dimension $n$. Let $S$ denote the tautological bundle over $G$. There is a canonical map on ...
- 129
7
votes
2
answers
291
views
Étendue measure of the set of lines between two Euclidean balls
Let $d>0$ and $r_1,r_2>0$ such that $r_1+r_2 < d$. Consider two (say, closed) balls $B_1,B_2$ in $\mathbb{R}^m$ having radii $r_1,r_2$ and whose centers are at distance $d$. Let $C$ be the ...
- 32.5k
2
votes
0
answers
134
views
Representations and action on Grassmannians
$\DeclareMathOperator\SO{SO}\DeclareMathOperator\Gr{Gr}$I came across a problem that could be formulated in term of Grassmannians, I would be very glad to have your opinion about it.
I have an ...
1
vote
1
answer
145
views
Zero loci of sections of wedge product of bundles
Let $V$ be a $\mathbf{C}$-vector space of dimension $n$, and consider the Grassmannian $G:=Gr(2, V)$ of 2-dim subspaces of $V$. Then we have the tautological subbundle $E\subset V\otimes \mathcal{O}_G$...
- 565
2
votes
1
answer
257
views
Grassmannian $\mathrm{Gr}(k, \pm \infty)$ in infinite dimension
$\DeclareMathOperator\Gr{Gr}$The Grassmnnian variety $\Gr(k,n)$ is the set of $k$-dimensional subspaces of $\mathbb{C}^n$. The coordinate ring $\mathbb{C}[\Gr(k,n)]$ is generated by Plucker ...
- 6,211
0
votes
0
answers
136
views
Understanding the relations without the knowledge of Plucker relations [duplicate]
Consider the grassmannian $\mathrm{Gr}(2,5)$. We know there is an embedding of $\mathrm{Gr}(2,5)$ into $\mathbb{P}^9$ by using the 10 Plucker coordinates, and they satisfy 5 Plucker relations. And, so ...
- 839
2
votes
0
answers
231
views
A question from Leon Simon's "Lectures on Geometric Measure Theory"
In a book I am reading (Leon Simon, Lectures on Geometric Measure Theory) at some point the author claims that if a certain property $(P)$ holds for almost every $n$-plane $\pi\subset \mathbb{R}^{n+k}$...
- 1,149
12
votes
1
answer
642
views
Is the appearance of Schur functions a coincidence?
The Schur functions are symmetric functions which appear in several different contexts:
The characters of the irreducible representations for the symmetric group (under the characteristic isometry).
...
- 193
1
vote
1
answer
98
views
Expected value of the projective metric between random orthogonal Stiefel matrices in $\mathbb{R}^{N \times k}$ equals $1 - \frac{k}{N}$
This is a cross-post from this other question that I asked ~1 month ago in the mathematics forum, with no reaction. I am still stuck on this, looking for references or approaches to proofs. I hope I ...
- 113
5
votes
0
answers
120
views
Representation-theoretic interpretation of double Schur polynomials
The Schur polynomials
$$s_\lambda(x_1, \ldots, x_n) = \frac{|x_i^{\lambda_j+n-j}|_{1\le i,j\le n}}{|x_i^{n-j}|_{1\le i,j\le n}}$$
naturally appear as polynomial representatives for Schubert classes in ...
- 3,446
1
vote
0
answers
179
views
The conditions to determine whether multivector $\Lambda\in\wedge^k V$ is decomposable
In Section 5, Chapter 1 of the famous book "Principles of algebraic geometry" by Griffiths and Harris, there are two equivalent conditions to determine whether a multivector $\Lambda\in\...
- 41
6
votes
0
answers
205
views
Quadric contain tangent variety of a curve in $\mathbb{P}^5$
Let $Q^4 \subset \mathbb{P}^5$ a smooth quadric over $\mathbb{C}$
which is via Pluecker map isomorphic
to Grassmannian of lines $\mathbb{G}(1,\mathbb{P}^3)$
in $\mathbb{P}^3$.
Consider following ...
- 619
1
vote
0
answers
133
views
Ideals whose alebraic variety is a singleton
I do not work in algebra, so i apologize in advance if there are some unclear/wrong sentences. Let us consider the ring $\mathbb{C}[X_1,\ldots,X_q]$ of polynomials in $q$ variables. For an ideal $I$ ...
- 121
2
votes
1
answer
83
views
Image of $H^0(C,\omega_C-x)$ in $G(g-1,H^0(C,\omega_C))$
Let $C$ be an algebraic curve over $\mathbb{C}$ and $\omega_C$ be its canonical bundle. We may assume that $C$ has genus $g\geq2$. Let $x\in C$ be an arbitrary point.
Question: What is the image of $...
- 439
3
votes
1
answer
289
views
Differential of a specific morphism to a Grassmannian
This is a problem that's been bugging me for some time, and therefore I've decided to ask it here. Let $X$ be a smooth projective (irreducible) variety over an algebraically closed field of ...
- 663
4
votes
1
answer
382
views
Universal hyperplane section and nondegeneracy of general hyperplane section
I have a question about Exercise 18.11 In Harris' book Algebraic Geometry, on page 231:
Give a proof of the nondegeneracy of the general hyperplane
section of an projective irreducible nondegenerated ...
- 5,966
6
votes
4
answers
486
views
The dimension of the Grassmannian cohomology ring $H^*(\mathrm{Gr}_{n,d})$ and the fundamental $\frak{sl}_n$-representation $V_{\pi_d}$
The vector space dimension of the cohomology group of the $2$-plane Grassmannian $\mathrm{Gr}_{2,n}$ is given by the number of tuples $(\lambda_1,\lambda_2)$ satisfying
$$
n - 2 \geq \lambda_1 \geq \...
1
vote
0
answers
98
views
Intersection of schubert varieties
Let $L_1$ and $L_2$ $\in$ $\mathbb{P}^4$ be two planes that intersect in exactly one point $Q$. Let $P_1 \in L_1$, $P_2 \in L_2$ points, such that $P_1 \neq Q \neq P_2$. Using the duality theorem, ...
- 11
2
votes
0
answers
256
views
How to perform this Gaussian matrix integral?
I'm reading this book The supersymmetric method in random matrix theory and applications to QCD. In page 302-303, the author calculate the following integral
$$
Z=\int d\psi \, dH \, P(H)\exp\left(-\...
- 375
7
votes
1
answer
310
views
Fundamental domain for two Grassmannians
Let $\pi_1, \pi_2$ be two $k$-dimensional subspaces of $\mathbb R^n$. Using elements of the orthogonal group $O(n)$, how much can we simplify $\pi_1, \pi_2$? Certainly there always exists $A \in O(n)$ ...
- 903
1
vote
0
answers
132
views
The geography of models of Fano varieties
This question aims to compute ${\rm Vol}(-K_X-tD)$ where $X$ is a $\mathbb{Q}$-factorial Fano variety of dimension $n$ and $D$ is a nonzero effective divisor on $X$. This volume is positive when $0\le ...
- 498
6
votes
0
answers
217
views
A Plücker coordinate matroid
Let $V$ be an $n$-dimensional vector space over a field $F$. Let
$\mathrm{Gr}(V,d)$ be the set (Grassmann variety) of all
$d$-dimensional subspaces of $V$. We can regard
$\mathrm{Gr}(V,d)$ as a subset ...
- 50.8k
0
votes
0
answers
350
views
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 ...
- 6,211
4
votes
0
answers
253
views
Does the space of hyperplanes in the Grassmannian have a name?
A way of defining the Grassmannian $Gr(k,n)$ is to consider the space of $k\times n$ matrices mod $GL(k)$ transformations on the rows. I'm interested in the space of $k\times 2n$ matrices mod $GL(k)$ ...
- 49
1
vote
0
answers
90
views
Non-trivial extension and tangent bundle isotropic Grassmannian
Let $V$ be a $2n$-dimensional vector space endowed with a nondegenerate skew-symmetric form $q:V \to V^\vee$. We define the isotropic Grassmannian to be
$$
X:=G_q(k,V)=\left\{[W] \in \mathbb P \left( \...
- 381
4
votes
0
answers
139
views
Reference request & more: compute vector bundles for homogeneous $G$-varieties
We work over the field of complex numbers $\mathbb C$.
Let $G$ be a simple linear algebraic group and let $P,Q$ be standard maximal parabolic subgroups of $G$ containing the same Borel subgroup $B$. ...
- 381
1
vote
0
answers
130
views
Generalize spinor bundles over orthogonal Grassmannians
We will work over $\mathbb C$ and the notation will be coherent with the paper of Ottaviani (see [Ott]).
Consider a $n$-dimensional quadric hypersurface $Q_n \subset \mathbb P^{n+1}$. We have ...
- 381
2
votes
0
answers
221
views
Transition maps between coordinate charts on the Grassmann manifold
Let $\mathbf{Gr}_{n,k}$ be the manifold of $k$-dimensional subspaces of $\mathbb{R}^n$, and let $\mathbf{col}$ be the map that takes a matrix in $\mathbb{R}^{n\times k}$ to its columnspace. The map
\...
- 21
2
votes
0
answers
266
views
Riemannian geometry of Grassmannian bundles
The Grassmannian bundle of a vector bundle $E$ is a smooth manifold where each fiber over the base space is replaced by the Grassmannian (of specified rank) of the fiber. I am interested in defining a ...
- 41
1
vote
0
answers
150
views
Counting non-zero Gramians of Grassmanians over finite field
In case of $\mathbb{F}_{2}$, we can obtain the number of all reduced row echelon forms (so called Grassmannians) for some m$\times$n full rank matrices by the following gaussian polynomial,
$$
\binom{...
- 11
5
votes
0
answers
169
views
Is the Grassmannian of a Banach space an infinite dimensional manifold?
Grassmannian of complemented subspaces in a Banach space is a Banach manifold. This is explained for example in the thesis of Douady and is rather analogous to the finite-dimensional case.
I would ...
- 344
11
votes
0
answers
211
views
Product on cellular cochains of the real Grassmannian
The real Grassmannian $Gr(k,n)$ of $k$-planes in $\Bbb R^n$ admits a Schubert cell decomposition, with one cell for each Young diagram $\lambda$ of height $\leq k$ and width $\leq (n-k)$; the ...
- 52.7k
3
votes
1
answer
429
views
A specific integration with Grassmann variables
I have recently read (for example, here) that this relation below is true
$$ \int dz \: e^{\frac{1}{2} \sum_{ij} z_i A_{ij} z_j} = Pf(\mathbf{A}),
$$
where $Pf(\mathbf{A})$ is the Pfaffian of an even ...
- 31
3
votes
1
answer
115
views
Given a subspace $U \subseteq S^d(V)$ of a particular form, does there always exist a complement of the form $S^d(W)$?
Let $V$ be a $\mathbb{C}$-vector space of dimension $N \geq 2$, let $d$ be a positive integer, let $l < N$ be a positive integer, and let $U \subseteq S^d(V)$ be a linear subspace of codimension $k=...
- 980
3
votes
1
answer
179
views
Given a subspace $U \subseteq S^d(V)$, does there always exist a complement of the form $S^d(W)$?
Let $V$ be a $\mathbb{C}$-vector space of dimension $N$, let $d$ be a positive integer, let $l \leq N$ be a positive integer, and let $U \subseteq S^d(V)$ be a linear subspace of codimension $k=\binom{...
- 980
1
vote
0
answers
202
views
What is the dimension of this subvariety of the Grassmannian?
Well, actually, what are the dimensions of the following two subvarieties of the Grassmannian. Let $N$ be a positive integer.
Let $V \subseteq \mathbb{C}^N$ be a linear subspace of dimension $N-k$ ...
- 980
3
votes
0
answers
241
views
Stability and simplicity of tangent sheaf of Grassmannian
Everything is over the complex numbers. Let $ X = \text{Gr}(k,n) $ be a Grassmannian variety and with tangent sheaf $ T_X $.
(1) Is $ T_X $ simple, i.e. is $\text{Hom} ( T_X, T_X) = \mathbb{C} $?
(2)...
- 936
7
votes
4
answers
477
views
What does $\mathbb E_V \max_{x \in V,\,\|x\|=1} x^T Ax$ evaluate to when $V$ is random $k$-dim suspace of $\mathbb R^n$ and $A$ is fixed psd matrix?
Let $G_{k,n}$ be the grassmannian of $k$-dimensional vector spaces of $\mathbb R^n$. By the Courant–Fisher characterization, the $k$th largest eigenvalue of an $n \times n$ psd matrix $A$ is given by
$...
- 6,853
2
votes
2
answers
288
views
Extensions for a short exact sequence on Grassmannians
$\DeclareMathOperator\Sym{Sym}\DeclareMathOperator\Ext{Ext}$Let us consider a $n$-dimensional complex vector space $V$ and denote by $G(k,n)$ the Grassmannian of $k$-planes in $V$. We use the ...
- 381
0
votes
0
answers
161
views
Projectivization of the normal bundle of $\mathbb P^4$ in the 10-spinor variety
Let $X=S_{10} \subset \mathbb P^{15}$ be the 10-dimensional spinor variety in its minimal embedding. Consider a $\mathbb P^4 \subset S_{10}$, hence we can define the normal bundle $N=N_{\mathbb P^4|S_{...
- 381
1
vote
0
answers
68
views
Generalized polynomials and a $4$-point cross-ratio function on the non-degenerate complex $4$-quadric
The Grassmannian $Gr_1(\mathbb{C}^2)$ is another name for $\mathbb{P}^1$. If one endows $\mathbb{C}^2$ with a complex symplectic form, or if one prefers (since this will allow us to generalize in ...
- 5,215
1
vote
0
answers
166
views
Dimension of the Grassmannian of lines of an hyperplane section
Let $X$ be an isotropic Grassmannian, $Pic(X)=\mathbb Z$ (for example $X$ is a projective space or a quadric hypersurface). Consider a global section $s \in \Gamma(X,L)$, where $L$ is the generator of ...
- 381
1
vote
0
answers
136
views
Globally generated sheaf arising from orthogonal Grassmannian
We will use the Grothendieck's notation, according to the book of Hartshorne.
Let us consider a finite dimension $\mathbb C$-vector space $V$, with a non-degenerate symmetric bilinear form $q:V \times ...
- 381