Questions tagged [symplectic-linear-algebra]
Questions about vector spaces equipped with a symplectic form, a non-degenerate, skew-symmetric bilinear form.
290 questions
0 votes
1 answer
34 views
Understanding the symplectic double extension
Let $(B,ω')$ be a symplectic Lie algebra. and the $\delta$ is a symplectic derivation, and $z\in B$. The double extension of $B$ is: $g=ℝe ⊕ B ⊕ ℝd$ as: Central Extension : $I = ℝe ⊕ B$,of $B$ with ...
1 vote
0 answers
49 views
Hodge star of a $(0,q)$-form wedged with the symplectic form on a symplectic manifold with a compatible almost complex structure
Let $(X,\omega)$ be a symplectic manifold of dimension $2n$ and $J$ be an almost complex structure compatible with $\omega$. In particular, $g(v,w):=\omega(v,Jw)$ defines a Riemannian metric, and ...
0 votes
0 answers
48 views
Are the matrices defined in the question elements of $Sp(1,4)$?
I was reading this paper which defines $L$ as "symplectic linear transformations, represented by unit-determinant $2 \times 2$" matrixes with entries in $\mathbb{F}_{4}$". For example, ...
1 vote
0 answers
62 views
A strange question on sum of intersections of Lagrangian subspaces equal to intersection of sum of them
In research I need to prove a very strange question about the sum of intersections of Lagrangian subspaces being equal to intersection of sum of Lagrangian subspaces. Why I say strange is that it ...
1 vote
0 answers
444 views
Counting the totally singular subspaces of a finite dimensional orthogonal vector space on GF(2)
A symplectic form on an $n$-dimensional vector space on $GF(2)$ is a symmetric, alternating bilinear form on the space. An orthogonal form $q$ on a space $V$ associated with a symplectic form $f$ is a ...
0 votes
1 answer
55 views
exercise from chapter 3 of Lectures on Symplectic Geometry by da Silva
I've skimmed through other posts on this book: Lectures on Symplectic Geometry by da Silva and am wrapping up a question from chapter 3. We have that $T^{*}X=M$ with the projection map $\pi: M\to X$. ...
0 votes
1 answer
105 views
Gromov width of an elipsoid
Suppose $E=\{ (x_1, x_2, y_1,y_2): \frac{x_1^2}{a_1^2} + \frac{x_2^2}{a_2^2} + \frac{y_1^2}{b_1^2} + \frac{y_2^2}{b_2^2} \leq 1 \}$. One defines $w_L(E)$ as the supremum of the $\pi r^2$ such that ...
1 vote
0 answers
47 views
Casimir functional for Vlasov-Poisson bracket
The following question is stated as exercise 10.2-2, p. 338 in the book "Introduction to Mechanics and Symmetry - 2nd Edition" by Marsden, Ratiu. Unless otherwise stated, all references ...
0 votes
0 answers
60 views
Computing the Weil representation
I am reading the lecture notes of Dipendra Prasad on the Weil representation and theta correspondence. There is quite a bit of notation but I will set it up here. $W$ is a symplectic space over a ...
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21 views
Existence of Invariant Lagrangian subspace
I am reading the following paper where the author says "It is a well-known fact that every symplectic operator on a finite-dimensional complex vector space has a Lagrangian invariant subspace.&...
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1 answer
90 views
Product Property of Maslov Index for Symplectic Matrices
I'm studying the Maslov index in McDuff and Salamon's Introduction to Symplectic Topology, 3rd edition. Theorem 2.2.12 develops the Maslov index for loops of symplectic matrices. In particular, let $r ...
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0 answers
56 views
Symplectic diagonalization of positive semi-definite matrices.
If $H$ is a positive definite matrix, it is well known by Williamson's theorem that one can brought $H$ into the block diagonal form $S^T H S = \begin{pmatrix} D & 0 \\ 0 & D \end{pmatrix}$ ...
1 vote
0 answers
54 views
Mutual orthogonality of hyperbolic planes in symplectic space
I am trying to prove the following theorem: Let $(V,\omega)$ be a finite-dimensional symplectic and let $W$ be a subspace of $V$. Let $W=W^{\text{rad}}\boxplus U$. Let $e_1,\cdots,e_r$ be a basis of $...
2 votes
1 answer
92 views
Order of group of isometries of a quadratic form in characteristic $2$
Let $V$ be an even dimensional vector space over the finite field $\mathbb{F}_\ell$ where $\ell$ is even, and set $n=\dim_{\mathbb{F}_\ell}(V)$. Let $q:V\to \mathbb{F}_\ell$ be a quadratic form, and ...
3 votes
2 answers
74 views
Interpreting a matrix equation with "matricised" eigenvalues
I am actually interested in understanding the relationship between eigenvalues of matrix $P \in \mathbb{C}^{n \times n}$ and matrix $Q \in \mathbb{R}^{2n \times 2n}$ defined as $$Q=\begin{pmatrix} \Re[...