Quadrics defined by skew-symmetric matrices

ASL structures of some quadrics

Let $K$ be a field and $X$, $Y$ denote matrices such that, the entries of $X$ are either indeterminates over $K$ or $0$ and the entries of $Y$ are indeterminates over $K$ which are different from those appearing in $X$. We consider ideals of the form $I_{1}(XY)$, which is the ideal generated by the $1\times 1$ minors of the matrix $XY$. We prove that the quotient ring $K[X, Y]/I_{1}(XY)$ admits an ASL structure for certain $X$ and $Y$.

$d$-sequence and Regular sequence of Quadrics

Let $K$ be a field and $X$, $Y$ denote matrices such that, the entries of $X$ are either indeterminates over $K$ or $0$ and the entries of $Y$ are indeterminates over $K$ which are different from those appearing in $X$. We consider ideals of the form $I_{1}(XY)$, which is the ideal generated by the homogeneous polynomials of degree $2$ given by the $1\times 1$ minors of the matrix $XY$. We prove that $d$-sequences and regular sequences arise naturally as part of generators of $I_{1}(XY)$ for some special cases. We use this information to calculate the equations defining the Rees algebra of $I_…

Cocharacters for the weak polynomial identities of the Lie algebra of $3\times 3$ skew-symmetric matrices

Let $so_3(K)$ be the Lie algebra of $3\times 3$ skew-symmetric matrices over a field $K$ of characteristic 0. The ideal $I(M_3(K),so_3(K))$ of the weak polynomial identities of the pair $(M_3(K),so_3(K))$ consists of the elements $f(x_1,\ldots,x_n)$ of the free associative algebra $K\langle X\rangle$ with the property that $f(a_1,\ldots,a_n)=0$ in the algebra $M_3(K)$ of all $3\times 3$ matrices for all $a_1,\ldots,a_n\in so_3(K)$. The generators of $I(M_3(K),so_3(K))$ were found by Razmyslov in the 1980's. In this paper the cocharacter sequence of $I(M_3(K),so_3(K))$ is computed. In other wor…

Nullities for a class of skew-symmetric Toeplitz band matrices

For all $n > k \ge 1$, we give formulas for the nullity $N(n,k)$ of the $n \times n$ skew-symmetric Toeplitz band matrix whose first $k$ superdiagonals have all entries $1$ and whose remaining superdiagonals have all entries $0$. This is accomplished by counting the number of cycles in certain directed graphs. As an application, for each fixed integer $z\ge 0$ and large fixed $k$, we give an asymptotic formula for the percentage of $n > k$ satisfying $N(n,k)=z$. For the purpose of rapid computation, an algorithm is devised that quickly computes $N(n,k)$ even for extremely large values of $n$ a…

Uniformly column sign-coherence and the existence of maximal green sequences

In this paper, we prove that each matrix in $M_{m\times n}(\mathbb Z_{\geq0})$ is uniformly column sign-coherent with respect to any $n\times n$ skew-symmetrizable integer matrix. Using such matrices, we introduce the definition of irreducible skew-symmatrizable matrix. Based on this, the existence of a maximal green sequence for a skew-symmetrizable matrices is reduced to the existence of a maximal green sequence for irreducible skew-symmetrizable matrices.

有向图广义共谱配对的上界：基于斜走矩阵的算术准则

An upper bound on generalized cospectral mates of oriented hraphs using skew-walk matrices

本文基于斜走矩阵的行列式算术准则，推导了有向图广义共谱配对数量的紧上界，并提出弱由广义斜谱决定的有向图判定准则，将图谱特性与网络系统可控性联系起来。