# Tagged Questions

**11**

votes

**1**answer

371 views

### An inequality for the spectral radius of matrices used by J. Bochi

I am interested in the history of an inequality for the spectral radius of a $d\times d$ real or complex matrix, which occurs in Jairo Bochi's 2002 article Inequalities for numerical invariants of ...

**5**

votes

**2**answers

113 views

### Induced matrix norm less than one for matrices with spectral radius less than one

Let $A$ be a square matrix with elements in $\mathbb{R}$ or $\mathbb{C}$,
$\rho\left(A\right)$ stands for the spectral radius of $A$, i.e.,
the maximum absolute eigenvalue of $A$; $A^{*}$ is the ...

**0**

votes

**0**answers

33 views

### If $A$ is doubly stochastic and reducible. Why is $A$ permutation similar to a matrix of the form $A_1 ⊕ A_2$

If $A \in M_n$ is doubly stochastic and reducible.
Why is $A$ permutation similar
to a matrix of the form $A_1 ⊕ A_2$, in which both $A_1$ and $A_2$ are doubly stochastic?

**1**

vote

**0**answers

64 views

### Let $M = \frac{1}{2}(A + {A^T})$ be real symmetric nonnegative matrix. Why does $\rho (A) \le {\lambda _{\max }}(M)$?

Let $A \in M_n$ be nonnegative, and consider the real symmetric nonnegative matrix
$M = \frac{1}{2}(A + {A^T})$.
Why does $\rho (A) \le {\lambda _{\max }}(M)$?

**1**

vote

**1**answer

78 views

### Multiplicatively closed subsets of $\mathbb{C}^{n \times n}$

While dealing with another problem I saw that I need to classify subspaces $V$ of $\mathbb{C}^{n \times n}$ that are multiplicatively closed.
So to get an idea of the nature of the subspaces I ...

**0**

votes

**1**answer

113 views

### Standard rational functions from matrices

In linear algebra we get introduced to standard polynomials that are associated to matrices such as characteristic polynomials and determinants.
What are some of the standard rational functions that ...

**1**

vote

**1**answer

72 views

### $0/1$ programming multiple quadratic constraints

If we have an $n$-variable rank $n$-linear system it is clear we can find whether there exists a $0/1$ solution in polynomial time.
If we have an $n$-variable degree $2$ system how many constraints ...

**0**

votes

**2**answers

338 views

### Solving a system of equations using Gröbner basis

In Sage (or any other package) when using Gröbner basis to solve a system of equations (some of which are non-linear equations) does computing the Gröbner basis for the ideal ID generated by the ...

**1**

vote

**0**answers

17 views

### How to find a subset of a matrix that has minimum condition number? [duplicate]

Suppose matrix $A$ is consist of M column vectors, how can we find a subset $B$, consisting of N column of $A$ (N＜M), that has minimum condition number (the ratio of maximum singular value by minimum ...

**0**

votes

**0**answers

49 views

### An extremal combinatorics problem

What is the minimum rank $r$ of an $n\times n$ square positive integer matrix such that sum of entries of every $\sqrt r\times\sqrt r$ submatrix is distinct and such that difference between minimum ...

**1**

vote

**0**answers

50 views

### How to associate the following two kinds of real polynomials?

Suppose the following real polynomial of $n$ variables
$$f(X_1,X_2,\cdots,X_n)=\sum_{I=(i_1,i_2,\cdots,i_n)}a_IX_1^{i_1}X_2^{i_2}\cdots X_n^{i_n}$$
is easy or familiar to us, but I need to deal with ...

**1**

vote

**0**answers

68 views

### A question on Perron–Frobenius theorem [closed]

Let $A \in M_n$ is nonnegative(all $a_{ij}\ge0$).
Suppose $A$ has a nonnegative eigenvector(all entries$\ge0$ ) with $r ≥ 1$ positive entries and $n − r$ zero entries.
Why is there a permutation ...

**4**

votes

**1**answer

119 views

### subset of hermitian matrices given by eigenvalues form a submanifold

Let $\mathcal{O}_\lambda$ be the set of hermitian $n+1 \times n+1$ matrices with Eigenvalues $\lambda = (\lambda_1, \dots, \lambda_{n+1})$.
and $\mathcal{O}^\mu$ the set of hermitian $n \times n$ ...

**6**

votes

**1**answer

184 views

### Bounds for maximum determinant of circulant matrices

The Hadamard circulant conjecture states that there do not exist circulant Hadamard matrices with more than $4$ columns.
An $n$ by $n$ Hadamard matrix where the entries are chosen from $\{-1,1\}$ ...

**2**

votes

**1**answer

74 views

### Heuristics for counting degrees of freedom

I have recently learned about the representation theorem for isotropic,
linear operators, which says the following:
Defintion:
Let $M_n$ be the vector space of $n \times n$ real matrices. We say a ...

**6**

votes

**1**answer

445 views

### Why is $(A^\perp)^\perp = A$?

On page 52 of this paper, Iwasawa considered the bilinear symmetric non-degenerate pairing $\Phi_n \times \Phi_n \rightarrow \mathbb{Q}_p/\mathbb{Z}_p$ defined by
$$\langle \alpha, \beta \rangle_n := ...

**1**

vote

**1**answer

175 views

### Solving Non-Linear Equations over a Finite Field of a Large Prime Order

I want to know is there is an efficient way to figure out whether or not a ( underdetermined) system of non-linear equations have a solution over a finite field of large prime order. The equations ...

**11**

votes

**4**answers

853 views

### Probability two products are equal

I am interested in the following simple looking problem on which I am stuck. Let $M$ be a fixed $m$ by $n$ matrix with $\pm1$ elements. Let $x$ and $y$ be two independently sampled random ...

**10**

votes

**2**answers

248 views

### Why Householder reflection is better than Givens rotation in dense linear algebra?

It’s obvious that Givens rotation works better with sparse matrices. But I don’t know why Householder reflection is better for dense matrices. Does it require less computations? Or it’s numerically ...

**3**

votes

**1**answer

185 views

### Why is dual lattice a lattice, in the context of complex tori

I have a simple linear algebra question regarding the definition of dual of a lattice; it was asked by someone else here three months ago on mathstackexchange but got no answer and few views, so ...

**0**

votes

**0**answers

234 views

### When does this matrix have full rank?

Suppose $\mathbf{B}\in\left[0,1\right]^{T\times M}$ is a binary matrix,
$\mathbf{B}_{i}$ is a column of $\mathbf{B}$, and $\mathbf{X}\in\mathbb{R}^{N\times T}$
is a matrix where the columns are ...

**2**

votes

**0**answers

118 views

### Which functions preserve the connectivity of graphs/components?

I am somewhat stuck working on an issue and would really love some guidance. I will state the problem, my current state and what led to it in case the solution lies beyond where I was looking
The ...

**0**

votes

**2**answers

65 views

### Simultaneous special orthogonal similarity problem

Given matrices $A,B,C,D\in\Bbb K^{n\times n}$ where $\Bbb K$ is a ring is there an efficient technique to compute set $O$ with $OO'=I$ where $'$ is transpose and $\mathsf{Det}(O)=\pm1$ such that
...

**0**

votes

**0**answers

54 views

### Simplifying product of matrix exponential?

Is there a known generalization for n-term matrix exponential multiplication?
I am aware that the Baker–Campbell–Hausdorff formula could be used, e.g.:
...

**1**

vote

**0**answers

95 views

### A linear combination problem

Given $0/1$ $n\times n$ matrix $M$.
Suppose we have $2$ vectors $\lambda,\mu\in\Bbb R^{1\times n}$ such that both
$$\lambda M\in\{0,1\}^{1\times n}$$
$$M\mu'\in\{0,1\}^{n\times 1}$$
holds with $'$ ...

**5**

votes

**1**answer

88 views

### Minimize Frobenius norm

My question is the following:
Suppose $M$ is an $n \times n$ symmetric real matrix. I want to find an $n \times n$ symmetric real matrix X such that $|| X -M||_F$ is minimized with the constraint ...

**5**

votes

**0**answers

199 views

### A combinatorial problem

What is the largest $m\times m$ $0/1$ matrix of real rank $n$ with every square submatrix sized at least ${n^{\gamma}}\times{n^{\gamma}}$ distinct for some fixed $\gamma>0$?
Upper Bounds: Number ...

**4**

votes

**0**answers

95 views

### A $0/1$ matrix problem

What is the largest $m\times m$ $0/1$ square matrix of rank $2n$ over $\Bbb R$ we can have such that every submatrix sized at least $n\times n$ has rank at least $\sqrt{n}$?

**1**

vote

**1**answer

61 views

### Reduced echelon form of sparce matrices and constructing hash function

Let $G$ be a $d$-regular graph, and $A$ be the incidence matrix of $G$. Also suppose $B$ is a reduced echelon form of $A$ such that computations are in $\mathbb F_2$. Given matrix $B$, can we find ...

**2**

votes

**1**answer

143 views

### Division and multiplication that preserve Euclidean norms

I am looking for ways to define
$$\frac{1}{x}\in \mathbb{R}^n\quad \quad and\quad \quad x\cdot y\in \mathbb{R}^n ,$$
where $x,y\in \mathbb{R}^n$ such that
...

**5**

votes

**1**answer

141 views

### Eigenvalues of $X$ in the metric of $Y$

What does this statement describe? $X$ and $Y$ are matrices.
The eigenvalues of $X$ in the metric of $Y$.
I've not seen this language used before in this fashion and I don't really know what ...

**0**

votes

**1**answer

44 views

### Is spectral properties a general term for condition number?

I am reading an article about solving large sparse linear systems, in this paper it’s said that most of the iterative methods to solve $Ax = b$ are very much influenced by the spectral properties of ...

**0**

votes

**0**answers

92 views

### Comparison of Parameter estimation using maximum likelihood and Maximum entropy

I am not sure if the question is appropriate but I want to try my luck. One can estimate a parameter using maximum likelihood and we know it is optimal. On the other hand there are methods which uses ...

**2**

votes

**1**answer

82 views

### Eigenvalues of product of symplectic matrices

I have 2 symplectic matrices $X_{1},X_{2} \in \mathbb{R}^{2n\times2n}$. The matrix $X=X_{1} \cdot X_{2}$ is also symplectic.
Question: Are there any theorems which allow me to express eigenvalues of ...

**1**

vote

**2**answers

60 views

### Sensitivity analysis in minimum norm problems under a linear constraint

Suppose $\Delta$ is some nice topological space, say compact, and Hausdorff.
Let $A:\Delta \rightarrow \mathbb{R}^{m\times n}$ be a continuous $m\times n$ matrix valued map. Let $b\in \mathbb{R}^{m}$ ...

**0**

votes

**0**answers

38 views

### Can the maximal eigenvalue of Toeplitz hermitian be bound by one entry?

Let $T$ be $N \times N$ toeplitz hermitian matrix. Assuming we control the entry $T_{N,1}$ with the other entries fixed. Can we determine the maximal eigenvalue of $T$, or at least bound it?

**9**

votes

**0**answers

155 views

### Is this generalization of eigenvalue and eigenvector studied?

While thinking about what it means for observables to be simultaneously measurable in quantum mechanics I came up with the following concepts, which I will call "linearly indexed" versions of standard ...

**0**

votes

**0**answers

44 views

### references for semi-linear algebra over fields

What is a good reference for semi-linear algebra? In particular semi-linear transformations and their matrix representations.

**7**

votes

**1**answer

100 views

### $\text{GL}(n + k, \mathbb{R})$ is a principal $H$ bundle over the Grassmann manifold $G_n(\mathbb{R}^{n+k})$?

Let $H$ be the subgroup of $\text{GL}(n + k, \mathbb{R})$ consisting of matrices whose lower $n \times k$ block is empty; i.e. consisting of matrices of the form$$\begin{pmatrix} A & * \\ 0 & ...

**5**

votes

**1**answer

160 views

### Continuity of solutions to $Av=b$

Let $X$ be a compact Hausdorff topological space, and $C(X)$ denote the ring of complex-valued, continuous functions on $X$. Let $A$ be a matrix with entries from $C(X)$ of size $m\times n$ and $b\in ...

**6**

votes

**1**answer

109 views

### Efficiently compute the trace of a sparse matrix times the inverse of a sparse matrix?

How can I efficiently compute
$\mathrm{trace}(A(B^{-1}))$
where $A$ and $B$ are both sparse symmetric PSD $n \times n$ matrices, both with $O(n)$ non-zero entries? If it helps, the pattern of ...

**9**

votes

**1**answer

451 views

### What is the spin connection in 9 dimensions as opposed to 5 dimensions?

From Spin Connection in 5 dimensions I can define a massless fermion's covariant derivative on a curved manifold as
$$
\nabla_\mu \psi = (\partial_\mu - {i \over 4} \omega_\mu^{ab} \sigma_{ab}) \psi
...

**4**

votes

**2**answers

254 views

### Is it always possible to “separate” the eigenvalues of an integer matrix?

Call a square matrix Galois-irreducible if all its eigenvalues are Galois conjugates of each other.
Let $M$ be an integer $n\times n$ matrix which is not Galois-irreducible. Is it always ...

**1**

vote

**1**answer

199 views

### Testing $0$ for a determinant like function [closed]

Given $A\in\Bbb Z^{n\times n}$ we have $$Det(A)=\sum_{\sigma\in S_n}(-1)^{sgn(\sigma)}\prod_{j=1}^nA_{j\sigma(j)}$$
We can test when this is $0$ by looking at the rank in polynomial time.
Can either ...

**4**

votes

**3**answers

119 views

### Fast Upper Triangular Matrix Exponentiation

Let $Q_n$ be a $n\times n$ matrix with $Q_n=\begin{pmatrix} -\lambda_1-\mu_1 & \lambda_1 & 0 & \cdots\\ 0 & -\lambda_2-\mu_2 & \lambda_2 & \cdots\\ \vdots & \vdots & ...

**1**

vote

**0**answers

43 views

### References for a minor variant of the Rayleigh quotient

I believe this variant of the Rayleigh quotient inequality must be well known but I could not find references for it online. It's proof is straightforward.
Let $\mathbf{A}\in\mathbb{R}^{n\times n}$ ...

**0**

votes

**1**answer

49 views

### Approximate $\mathbf{G}=(a\mathbf{H}+\mathbf{M})^+$ by Taylor expansion [closed]

Suppose we have a complex matrix $\mathbf{M}$. Let $\mathbf{M}^+=(\mathbf{M}^*\mathbf{M})^{-1}\mathbf{M}^*$ be the pseudo-inverse of $\mathbf{M}$, where $^*$ denotes the conjugate transpose. Let ...

**10**

votes

**1**answer

191 views

### On Sampling rank $r$ matrices

Sample $n^2$ integers $a_{11},\dots,a_{nn}$ in $\{-d,\dots,-1,0,1\dots,d\}$ uniformly.
What is the probability that the resulting matrix $[a_{ij}]$ has rank $r$?
Is there a nice parametrization of ...

**6**

votes

**1**answer

270 views

### Encyclopedia of properties of nonnegative matrices

I'd like to buy a book that contains more or less all known properties of elementwise nonnegative nonnegative matrices, i.e. matrices $A$ such that $A_{i,j}\geq 0$ for all $i,j$.
Chapter 8 in ...

**1**

vote

**2**answers

74 views

### Orthogonal Procrustes problem with Absolute Values

Given a non-negative matrix $T$, how to find a orthogonal matrix $O$ minimising
$$ \left\lVert \, |O| - T \right\lVert_F,$$
where $\lVert \cdot \lVert_F$ denotes the Frobenius norm, and $| \cdot |$ ...