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Questions about the properties of vector spaces and linear transformations, including linear systems in general.
4
votes
Accepted
Solving a recursion for polynomials defined by a matrix product
Your polynomial is precisely
$$
\sum_{k_1+2k_2+\cdots+nk_n=n}\binom{k_1+\cdots+k_n}{k_1,\ldots,k_n}X_1^{k_1}\cdots X_n^{k_n}.
$$
The proof is straightforward by induction: you have
$$
p_n(X)=\sum_{i= …
1
vote
A (bi)alternant formula for Wronskian
There is an instance where the two formulas are very close: if $f_1,\ldots,f_n$ are fundamental solutions of a linear ODE with indeterminate (constant) coefficients. This is explained in the elegant p …
3
votes
0
answers
114
views
Checking the generic rank of a matrix
Suppose that $A,B\in M_{p,q}(\mathbb{Z})$ are two rectangular integer matrices of the same size. Suppose that one has a conjecture stating that the rank of the matrix $A+tB$ for Zariski generic values …
2
votes
Inner products on super vector spaces
In addition to the other answer, a very good reference on that matter is the book of Yuri Ivanovich Manin "Gauge Field Theory and Complex Geometry", specifically Chapter 3 "Introduction to superalgebr …
20
votes
Is there a version of inclusion/exclusion for vector spaces?
One way to look at this question is via quiver representations. Two subspaces of a vector space form a representation of the quiver $A_3$ with orientations $\bullet \rightarrow \bullet \leftarrow \bul …
4
votes
Accepted
What do you call a scaled orthogonal map?
Wikipedia suggests "conformal orthogonal group" for the group of all such maps; see the articles
https://en.wikipedia.org/wiki/Conformal_group
https://en.wikipedia.org/wiki/Orthogonal_group#Conformal_ …
4
votes
Vacuum vector and basis defined by anti-commuting operators
There is a general algebraic result which states that the abstractly defined associative $\mathbb{R}$-algebra with generators $X_1,\ldots,X_n$, $Y_1,\ldots,Y_n$ and relations
$$
X_iX_j+X_jX_i=0, \qua …
5
votes
Accepted
Can the concatenation of projection operators be nilpotent with an index k>=3?
I think your example is easily generalisable for any index. For example, let
$$
Q_1=P_1\oplus(1),
Q_2=P_2\oplus(1),
Q_3=P_3\oplus(1)=(1)\oplus P_1,
Q_4=(1)\oplus P_2,
Q_5=(1)\oplus P_3.
$$
Then $Q_5 …
4
votes
Accepted
An $n$ eigenvalue multiplicity
This is an elaboration on the comment of Alexandre Eremenko. Algebraic multiplicity $n$ means that we have the equality of polynomials
$$
\det(t I_n -a_1A_1+\cdots+a_nA_n)=(t-\lambda)^n
$$
for some $ …
8
votes
Accepted
Solving multilinear equations
Multilinear equations are hardly easier than general equations. For instance, the multilinear equations
$$
\begin{cases}
x_0-x_1=0,\\
x_0x_1-x_2=0,\\
x_0x_2-x_3=0,\\
\ldots\\
x_0x_{n-1}-x_n=0
\end{c …
6
votes
Accepted
Set of integer matrices $A$ such that $(A^k)_{k\in\mathbb{N}}$ is eventually periodic
Of course. The eigenvalues of this matrix (over $\mathbb{C}$) may only be zeros and roots of unity (whose minimal polynomial is of degree at most $n$, as they are roots of the characteristic polynomia …
10
votes
An Linear Algebra Inequality
If you replace determinants by traces, then this inequality is just Cauchy-Schwarz for the inner product $(X,Y)=\mathop{\mathrm{tr}}(XY^T)$ on the space of matrices. Now, we just have to recall that d …
1
vote
Relation between degree of root of determinant polynomial and rank of the matrix
From your more general question I infer that you want to look at the coset of your matrix in the quotient (not at evaluation at specific $x_1,\ldots,x_n\in\mathbb{F}_q$).
Without loss of generality, …
1
vote
Multivariate analogue of Vandermonde determinant
FWIW, for $n=d=2$, this polynomial is irreducible, as I just checked in Magma. The naive code for this (which even the online calculator http://magma.maths.usyd.edu.au/calc/ can handle) is
S<x1,x2,x3 …
35
votes
Injectivity implies surjectivity
There is an improvement of the answer of Joseph Van Name which I feel is much more in the spirit in the question asked:
Let $(X,d)$ be a compact metric space, and assume that the mapping $f\colon X\t …