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The study of the properties of real and complex matrices that are more close to analysis and operator theory. For instance: the properties of positive definite matrices, matrix inequalities, perturbation analysis, matrix functions, inequalities between eigenvectors and singular values, majorization.

1 vote
3 answers
195 views

The functional equation $T(x\otimes y)=T(x)\otimes T(y)$ on the matrix algebra

Is there a non trivial sequence $(T_{n})$ of linear operators $T_{n}$ on $M_{n}(\mathbb{C})$ such that $$T_{nm}(X\otimes Y)=T_{n}(X) \otimes T_{m}(Y) $$ where $X$ and $Y$ are in $M_{n}(\mathbb{C})$ …
Ali Taghavi's user avatar
1 vote
1 answer
459 views

Is this a full rank matrix? [closed]

According to the answer of znt to the previous version, I revise the question as follows: Is there a real $(n-1)\times n$ matrix $A$ such that $A$ is not a full rank matrix and satisfy $a_{ii} …
Ali Taghavi's user avatar
5 votes
1 answer
186 views

Is a pointwise " simple tensor" valued continuous map a tensor product of two continuous maps?

A matrix $A\in M_{4}(\mathbb{C})$ is called a simple tensor if $A=B\otimes C$ for two $2\times 2$ matrices $B,C$. Assume that $X$ is a Hausdorff topological space.Assume that $f:X\to M_{4}(\m …
Ali Taghavi's user avatar
7 votes
Accepted

A matrix norm inequality II

No the norm of the left side can be very large. For example $\left\| X^{-1}AXB \right\| $ is an unbounded function in $(x,y)$ where $A,X,B$ are the following matrices: Put $A=B= \begi …
Ali Taghavi's user avatar
2 votes

Unitary factor in polar decompositions

I think that the part $(a)$ of proposition $2.4$ of this paper shows that for $n$ sufficiently large one can construct a $n \times n$ unitary matrix $U=-I_{2}\oplus U'$, which can be decomp …
Ali Taghavi's user avatar
2 votes
1 answer
261 views

A certain subset of general linear group

Motivated by the concept of diagonally dominated matrices we consider the space $S$ of all complex $n\times n$ matrices with $|a_{ii}|>\sum_{j\neq i} |a_{ij}|$, for every $i$. Every elemen …
Ali Taghavi's user avatar
0 votes
1 answer
147 views

Is it a sufficient condition for linearity?

Edit: According to the comment by LSpice we come back to the initial version of this question Let $f:\mathbb{R}^n\to \mathbb{R}^n$ be a smooth function such that for every $x\in \mathbb{R}^n$ the der …
Ali Taghavi's user avatar
2 votes

Is the linear span of special orthogonal matrices equal to the whole space of $N\times N$ ma...

It is sufficient to prove the statement in the question only for matrices in the form $[1]_{1\times 1}\oplus [0]_{k}$, that is the rank-1 projections or $$\begin{pmatrix} 0&\lambda\\ -\lambda …
Ali Taghavi's user avatar
3 votes
1 answer
171 views

Representation of $4\times4$ matrices in the form of $\sum B_i\otimes C_i$

Every matrix $A\in M_4(\mathbb{R})$ can be represented in the form of $$A=\sum_{i=1}^{n(A)} B_i\otimes C_i$$ for $B_i,C_i\in M_2(\mathbb{R})$. What is the least uniform upper bound $M$ for such $n(A) …
Ali Taghavi's user avatar
0 votes
1 answer
199 views

Riemannian metrics on matrix space for which the restriction of trace function to each compl...

Edit: According to comment by Leo Monsaingeon I revise my question: Is there a Riemannian metric on $M_n(\mathbb{R})$ for which the function $trace$ is a bounded function on every complete(whole …
Ali Taghavi's user avatar
3 votes
1 answer
538 views

The Matrix form of the Van der Pol equation

Motivated by the classical Van der Pol equation which has a unique periodic attractor, we consider the following differential equation on $M_{2}(\mathbb{R})\times M_{2}(\mathbb{R}):$ $$(*)\;\;\;\b …
Ali Taghavi's user avatar
6 votes
1 answer
751 views

Is every real matrix conjugate to a semi antisymmetric matrix?

Is it true to say that every matrix $A\in M_n(\mathbb{R})$ is similar (conjugate) to a matrix $B=(b_{ij})$ with $b_{ij}=-b_{ji}$ for all $i\neq j$?(With some abuse of terminology,a matrix $B$ with th …
Ali Taghavi's user avatar
3 votes
Accepted

Can we classify the general linear maps such that for a fixed matrix $A \in M_n(\mathbb R)$ ...

One can not say that $\mathcal E$ is always connected. For $n=3, $(and similarly $n>3$) let $A$ be a matrix with $a_{i1}=1,\quad \forall i \in \{1,2,\ldots,n\} $ Then $\mathcal E$ conta …
Ali Taghavi's user avatar
29 votes
1 answer
3k views

Is there an explicit formula for the hessian of "Determinant"?

Let $f: G= \mbox{GL}(n,\mathbb{R}) \to \mathbb{R}$ be the determinant function. Then $\mbox{Hess} (f)$ is a two linear map on $M_{n}(\mathbb{R})\simeq T_{e}(G)$ where $e$ is the neutral element of $G$ …
Ali Taghavi's user avatar