Questions tagged [matrices]

Questions where the notion matrix has an important or crucial role (for the latter, note the tag matrix-theory for potential use). Matrices appear in various parts of mathematics, and this tag is typically combined with other tags to make the general subject clear, such as an appropriate top-level tag ra.rings-and-algebras, co.combinatorics, etc. and other tags that might be applicable. There are also several more specialized tags concerning matrices.

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Condition number after some "non standard" transform

Given a positive definite matrix $A$, and a diagonal matrix $B$ with positive diagonal entries, is the following inequality generally true? $$\kappa((A + B)(I + B)^{-1}) \leq \kappa(A)$$ $I$ is an ...
randomprojection's user avatar
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Unique upper triangular basis matrix of sublattice $\Lambda \subseteq \mathbb{Z}^n$

Let $\Lambda \subseteq \mathbb{Z}^n$ be a full rank sublattice. We find an upper triangular basis matrix $B \in \mathfrak{ut}(\mathbb{Z},n)$ of $\Lambda$. Is $B$ unique up to the right action of $\...
Bipolar Minds's user avatar
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Bounding the number of information sets in a linear binary code

A pretty well-known theorem regarding linear $(n,k,d)$ codes is that every $n-d+1$ coordinate positions contain an information set, but not all $n-d$ coordinate positions do. This is equivalent to a ...
Benjamin Lindqvist's user avatar
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How to construct large sets of $m$-dimensional vectors over a finite field such that any $m$ of them are independent?

Let $m\ge 2$ be an integer and $\mathbb{F}$ be a finite field of order $p^k$. I want to construct as many as possible $m$-dimensional vectors $v_1,v_2,\ldots,v_n$ in field $\mathbb{F}$ such that any $...
W. Wang's user avatar
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On a matrix algorithm involving rank-one projections

Let $\{v_i\}_{i=1}^N$ be a set of $n$-dimensional real vectors spanning $\mathbb{R}^n$. Let $p\in [0,1]$ be a rational number and consider the iteration \begin{equation} X_{k+1}=\frac{1}{N}\sum_{i=1}^...
Ludwig's user avatar
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When is $\left[\begin{smallmatrix} D_1 & B \\\\ -B^T & D_2 \end{smallmatrix} \right]$ $\mathbb{R}$-diagonalizable?

Is there some block-wise characterization of $\mathbb{R}$-diagonalizability (by similarities) of $$\begin{bmatrix} D_1 & B \\\\ -B^T & D_2 \end{bmatrix},$$ where $D_1$ and $D_2$ are real ...
Vedran Šego's user avatar
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Relating Numerical Range and Perron-frobenius theorem for positive matrices?

Let $A$ be any matrix with all entries positive (which means Perron-Frobenius theorem can be applied). Then its numerical range is defined as the set of complex numbers $$W(A)=\{x^HAx\lvert ~x^Hx=1\}$$...
dineshdileep's user avatar
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Rank of a particular matrix

Denote $P_{2n}$ to be collection of homogeneous total degree $2$ real polynomials in exactly $2n$ variables such that coefficient of every monomial is either $1$ or $-1$. Split variable set into ...
Turbo's user avatar
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Spectral radius of a column stochastic matrix perturbed by a rank-1 matrix

$P\in \mathbb{R}^{n\times n}$ is an irreducible column stochastic matrix. $P$ is also diagonally dominant. $w \in \mathbb{R}^{n} $ is a strictly positive vector satisfying $w^T \mathbf{1} = 1$ where $\...
vansy's user avatar
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Can anyone help me deduce a matrix inequality?

The following lemma is taken from references firstly. Lemma 1 [1-2] Given matrices $Q=Q^{T} , F, M$ and $N$ of appropriate dimensions, then $$Q+MFN+N^{T}F^{T}M^{T}<0$$ for all $F$ satisfying $F^{...
lovewinter's user avatar
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147 views

Copositivity under tensor products

Is there any symmetric real matrix $A$ such that $A^{\otimes n}$ is copositive for all positive integers $n$, but such that A is neither positive semidefinite nor has just non-negative entries? ...
Miguel's user avatar
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Commutative decomposition for full-rank $A$ and low-rank $B$ matrices that do not commute

1. Motivation Consider symmetric matrices $A,B\in\mathbb{R}^{n\times n}$, and let $A$ be full-rank and $B$ be low-rank. The simultaneous block-diagonalization, defined as the following $$A=V_{1}\...
Richard Zhang's user avatar
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$\epsilon$-covering number of a set of rank-2 matrices

Suppose that two unit-norm vectors $\boldsymbol{a}\in \mathbb{R}^m$ and $\boldsymbol{b}\in\mathbb{R}^n$ are given with $m\leq n$. Furthermore, let $\boldsymbol{F}_{m,n}$ denote the first $m$ rows of ...
S.B.'s user avatar
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On increasing the penalty term in convex optimization with regularization

Given the two strictly convex (unique solution) optimization problems as: $$Problem\:1:\min_{X} f(X)+\|X\|_{F}^2 \hspace{2cm}Problem \:2:\min_{X}f(X)+n\|X\|_2^2$$ where $X\in\mathbf{S}_{++}^{n}$ (...
borntotry83's user avatar
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Reducing $\ell_1$ norm of non-full-rank matrices

I have two matrices ${\bf{X}}_{p\times r}$ and ${\bf{Y}}_{r\times q}$ with $r<\min(p,q)$. Matrix ${\bf Y}$ does not have full row rank (i.e., rank$({\bf Y})<r$). Can I build two new matrices ${\...
Mkl's user avatar
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Invexity of the $L_2$ norm

I have the following function: $ f({\bf A,b}) = \| {\bf y - XAb} \|_2^2$ where ${\bf y}_{n \times 1}$ and ${\bf X}_{n \times p}$ are fixed, and ${\bf A}_{p \times r}$ and ${\bf b}_{r,1}$ are the ...
Mkl's user avatar
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the annihilator of cokernel in a particular case

Let $A\in Mat(m,n;R)$ for $m\le n$ and $R$ a local ring. Consider the $mn\times(m^2+n^2)$ matrix $A\otimes 1_{nn}\oplus 1_{mm}\otimes A^T$, here $1_{mm}$, $1_{nn}$ are identity matrices. I'd like to ...
Dmitry Kerner's user avatar
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188 views

Method to Generate Random Mutually Orthogonal Unitary Matrices

The title says it all, I'd like to know if such a method exists to generate random mutually orthogonal unitary matrices. If so, any supplementary references would be very much obliged. Thanks again!
Vincent Russo's user avatar
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516 views

Cavalieri's principle and inversion of the Vandermonde matrix

There are many examples on the Web of the use of Cavalieri's principle in determining areas and volumes of 2-D and 3-D geometrical figures. The Wikipedia link uses the principle as both a proof and ...
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Closed-form solution to a system of linear equations

Consider the following $n \times n$ matrix with a particularly nice structure: \begin{equation}\mathbf{P}=\begin{pmatrix} 0 & 0& \dots&0 & 0 &1\\ 0 & 0& \dots&0 & \...
MthQ's user avatar
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124 views

Large prime divisors in entries of matrix powers

Are any examples known of an integer matrix $A$, such that the largest prime divisor of some specified entry of $A^n$ grows exponentially in $n$? How about where it just grows strictly faster than any ...
Tobias Kildetoft's user avatar
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463 views

An optimization problem over real symmetric matrices

Given an $n\times s$ matrix $P$ of positive real numbers and $T\geq n$, find (either by a formula or an algorithm) the real symmetric $n\times n$ Z-matrix $A$ which maximizes $\min\limits_{1\leq i<...
Binzhou Xia's user avatar
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0 answers
197 views

A similarity problem over matrices over Gaussian integers

Let $R = \mathbb Z[\sqrt{-1}]$ and $$\Omega = \{X \in GL_4(R) : X \overline X = I_4 \text{ or } -I_4 \},$$ where $\overline X$ is the complex conjugate matrix of $X$. Two matrices $A, B \in \Omega ...
Basics's user avatar
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Beating Kadane's Algorithm

I am seeking some reference on already existing work for the following problem. Given an $n$-dimensional square matrix $A=DP$ where $D$ is a diagonal and $P$ is a permutation matrix (think of Gaussian ...
Predrag Punosevac's user avatar
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123 views

Copositivity in matrix pencils

Given two square symmetric matrices $A,B$ of the same order, the matrix pencil $P(A,B)$ is the set of linear combinations of $A$ and $B$. Finsler's theorem gives an elegant criterion for $P(A,B)$ to ...
Felix Goldberg's user avatar
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Matrix-tree for matrices with constant diagonal

I've got a symmetric matrix $A$ whose entries are in $\{0,-1,1\}$, with the diagonal entries all equal to $1$. I'm interested in finding a combinatorial description of the entries of the inverse of $A$...
Felix Goldberg's user avatar
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0 answers
333 views

when upper triangular matrix modulo prime ideals implies upper triangular?

Let $E/ \mathbb{Q}_p$ be a finite extension, let $\mathcal{O}$ be the ring of integers of $E$. Let $A$ be a reduced noetherian local complete $\mathcal{O}$-algebra with the maximal ideal $\mathfrak{m}$...
Przemyslaw Chojecki's user avatar
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544 views

Canonical forms for block-positive-definite matrices

Suppose we are given a block $2\times 2$ matrix that is positive-definite, and let's suppose for simplicity that the blocks along the main diagonal are the identity. So $$ \begin{bmatrix} I & X \\\...
Laurent Lessard's user avatar
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229 views

Matrix where every subset of rows has maximal rank

I am looking for a class of matrices $M(n(m), m, k(m), \phi)$ with the following properties: M is $n \times m$ where $n(m) > m$. Every subset of rows of size $k$ has (maximal) rank $m$. $n(m)$ ...
aelguindy's user avatar
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0 answers
217 views

Eigenvalues vs.matrix sparsity

For an n X n matrix whose entries are constrained to be in some [x,y], is the maximum absolute eigenvalue of the matrix a function of its sparsity? Is there a closed-form expression that states this ...
Maniacka's user avatar
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0 answers
1k views

Matrix Operations Preserving Hurwitz Stability

I begin with terminology I use in the question. A real square matrix $A$ is negative-stable if for every eigenvalue $\lambda$ of $A$, ${\mathrm{Re}}(\lambda) < 0$; $\ast$-negative-stable if for ...
Gilles Gnacadja's user avatar
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0 answers
161 views

Does the following characterization of subgroups of $GL_2(\mathbb{F}_p)$ generalise?

Let $p$ be a prime number. By a Cartan subgroup of $GL_n(\mathbb{F}_p)$ I mean an absolutely semisimple maximal abelian subgroup. When $n=2$, it is well-known* that, for $G \subset GL_n(\mathbb{F}_p)$...
Barinder Banwait's user avatar
3 votes
0 answers
220 views

Could SVD be used to optimize the partial inner-products?

Suppose a set $N$ of $n$ distinct points in $m-$dimensional space is given in $X\in\mathbb{R}^{n\times m}$. Also, suppose a subset $L\subset N$, $|L|=l<m<n$, with $m-$dimensional coordinates in ...
usero's user avatar
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237 views

criterion for deciding whether the product of a sequence of Givens rotations can reach the full special orthogonal group

By Givens' rotation $R(1,2;\theta)$ I mean a matrix which has the $$\begin{pmatrix} \hphantom{-}\cos \theta &\sin \theta \cr -\sin \theta & \cos \theta \end{pmatrix}$$ $2 \times 2$ block at ...
John Jiang's user avatar
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3 votes
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514 views

A question about the generalized Lidskii-Wielandt inequality for matrices proved by Thompson and Freede

In 1971, Thomson and Freede generalized the Lidskii-Wielandt inequalites as follows (version for singular values) Let $A$, $B$ be $n\times n$ Hermitian matrices. Suppose $\alpha_1\geq \alpha_2 \geq \...
user11870's user avatar
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0 answers
358 views

Do Isometry Groups Tell Us How Difficult Norms are to Compute?

The question: Consider two norms N1 and N2 on the space of n-by-n complex matrices. N1 and N2 have the same isometry group and computing N1 is NP-HARD. Does it follow that computing N2 is NP-HARD as ...
Nathaniel Johnston's user avatar
3 votes
1 answer
764 views

Real part of eigenvalues and Laplacian

I am working on imaging and I am a bit puzzled by the behaviour of this matrix: $$A:=\left( \begin{array}{cccccc} 1 & 0 & 0 & -1 & 0 & 0 \\ 0 & 0 & 0 & 0 & -1 &...
user avatar
3 votes
1 answer
719 views

Finding an adjacency matrix whose cube's diagonal is equal to a given vector

How can I find all binary matrices $A$ such that $A^3$ is a non-negative, integer square matrix and $$\mbox{diag}\left(A^3\right)=b$$ for some given vector $b$? Is there a way to characterize all ...
Student88's user avatar
  • 503
2 votes
0 answers
43 views

Relationship between the homology of two types of tensor products of $\mathbb{Z}/ 2 \mathbb{Z}$-graded objects?

Let's consider a $2$-periodic complex $F$ of free $R$-modules, which is just a $\mathbb{Z} / 2 \mathbb{Z}$-graded complex $$F_1 \xrightarrow{d_1} F_0 \xrightarrow{d_0} F_1$$ (really the arrow $d_0$ ...
Rellek's user avatar
  • 401
2 votes
0 answers
248 views

Two questions about three circulant matrices

Consider the following matrix equation in $n \times n$ circulant $\pm 1$ matrices $A$, $B$, $C$ $$2AA^T+BB^T+CC^T=(4n+4)I-4J$$ where $I$ is the $n \times n$ identity matrix and $J$ is the $n×n$ matrix ...
user369335's user avatar
2 votes
0 answers
143 views

What are the name and inverse of an interesting integer matrix?

It is practicable to compute the matrix inverses \begin{align*} \begin{pmatrix} 1 & 0 & 0 \\ 1 & 1 & 1 \\ 1 & 2 & 2^2 \\ \end{pmatrix}^{-1} &=\begin{pmatrix} 1 & 0 &...
qifeng618's user avatar
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2 votes
1 answer
141 views

Upper bound for the rank of a Gram-type matrix

Let $V = (v_{1},...,v_{N})$ and $W = (w_{1},...,w_{N})$ be 2 sets, each containing $N$ vectors from $\mathbb{R}^{n}$; i.e, $v_{j}, w_{j} \in \mathbb{R}^{n}$ for all $1 \leq j \leq N$. Assume that $N$ ...
Tomer Milo's user avatar
2 votes
0 answers
113 views

What is the quantity $\sqrt{\frac{c^2+d^2}{a^2+b^2}}$ of a matrix with determinant one?

Suppose that $A \in \mathbb R^{2 \times 2}$ has determinant one, $$ A = \begin{pmatrix} a & b \\ c & d \end{pmatrix} $$ I'm currently working on a problem where I obtained a condition on the ...
Muzi's user avatar
  • 163
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0 answers
118 views

Decompose a rational matrix as an integer matrix and an inverse of integer matrix

Suppose we have a non-singular rational matrix $Q$, consider the the $\mathbb{Z}$-span of the columns of $Q$ and $Q^{-1}$, denote it as $H = {\rm Span}_{\mathbb Z} \{ Q(\mathbb Z^{n}), Q^{-1}(\...
ghc1997's user avatar
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2 votes
0 answers
47 views

What conclusions can I derive from this family of trace inequalities?

Problem. Let $n_1,\ldots,n_s,m_1,\ldots,m_s\ge 0$ be nonnegative integers and set $m := \sum_{i=1}^s m_i$ and $n := \sum_{i=1}^s n_i$. Let $\oplus$ be an operation on matrices which stacks them in a ...
eepperly16's user avatar
2 votes
0 answers
294 views

Dimension of a subspace of $n\times n$ real symmetric matrices

Let $n\in \mathbb N.$ Let $W$ be a non-trivial subspace of $n\times n$ symmetric matrices such that for every $x\in \mathbb R^n\setminus \{0\}$ there exists $a_x\in \mathbb R^n\setminus \{0\}$ such ...
mathew's user avatar
  • 21
2 votes
0 answers
129 views

Permutation similarity of matrices with many distinct entries

This is related to graph isomorphism. Here matrices are square $n \times n$ with non-negative integer entries. Two matrices $A,B$ are permutation similar if there exist permutation matrix $P$ such ...
joro's user avatar
  • 24.2k
2 votes
0 answers
70 views

The probability that the dominant eigenvalue of a random real matrix is real

Let $X_n$ be an $n\times n$ real matrix where the entries in $X_n$ are independent, normally distributed, have mean $0$, and variance $1$. Suppose that $\lambda_1,\dots,\lambda_n$ are the eigenvalues ...
Joseph Van Name's user avatar
2 votes
0 answers
87 views

decidability special case of column generation problem

I have the following problem: Input: sub-spaces $V_1, \dots, V_d$ of $\mathbb{Z}^{d}$ Question: are there $v_i \in V_i$ such that the matrix $(v_1, \dots, v_d)$ has determinant $\pm 1$ (equivalently, ...
Armin Weiß's user avatar
2 votes
1 answer
131 views

Generate a low-rank sparse covariance matrix

May I ask how to generate a low-rank sparse covariance matrix? Thank you!
JWRebecca's user avatar

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