Searcharxiv⌕ Search

arXiv subjects

Pudji Astuti

Publications and source records attributed to Pudji Astuti.

11 recordsLinked to original sources
arXiv2021

On bases and the dimensions of twisted centralizer codes

Alahmadi et al. ["Twisted centralizer codes", \emph{Linear Algebra and its Applications} {\bf 524} (2017) 235-249.] introduced the notion of twisted centralizer codes, $\mathcal{C}_{\mathbb{F}_q}(A,\gamma),$ defined as \[ \mathcal{C}_{\mathbb{F}_q}(A,\gamma)=\lbrace X \in \mathbb{F}_q^{n \times n}:~\ AX=\gamma XA\rbrace, \] for $A \in \mathbb{F}_q^{n \times n},$ and $\gamma \in \mathbb{F}_q.$ Moreover, Alahmadi et al. ["On the dimension of twisted centralizer codes", \emph{Finite Fields and Their Applications} {\bf 48} (2017) 43-59.] also investigated the dimension of such codes and obtained upper and lower bounds for the dimension, and the exact value of the dimension only for cyclic or diagonalizable matrices $A.$ Generalizing and sharpening Alahmadi et al.'s results, in this paper, we determine the exact value of the dimension as well as provide an algorithm to construct an explicit basis of the codes for any given matrix $A.$

cs.IT↗
arXiv2018

Pairs of Modules over a Principal Ideal Domain

We study pairs of finitely generated modules over a principal ideal domain and their corresponding matrix representations. We introduce equivalence relations for such pairs and determine invariants and canonical forms.

math.AC↗
arXiv2016

Hyperinvariant, characteristic and marked subspaces

Let $V$ be a finite dimensional vector space over a field $K$ and $f$ a $K$-endomorphism of $V$. In this paper we study three types of $f$-invariant subspaces, namely hyperinvariant subspaces, which are invariant under all endomorphisms of $V$ that commute with $f$, characteristic subspaces, which remain fixed under all automorphisms of $V$ that commute with $f$, and marked subspaces, which have a Jordan basis (with respect to $f_{|X}$) that can be extended to a Jordan basis of $V$. We show that a subspace is hyperinvariant if and only if it is characteristic and marked. If $K$ has more than two elements then each characteristic subspace is hyperinvariant.

math.RA↗
arXiv2016

Characteristic and hyperinvariant subspaces over the field GF(2)

Let $f$ be an endomorphism of a vector space $V$ over a field $K$. An $f$-invariant subspace $X \subseteq V$ is called hyperinvariant (respectively characteristic) if $X$ is invariant under all endomorphisms (respectively automorphisms) that commute with $f$. If $|K| > 2$ then all characteristic subspaces are hyperinvariant. If $|K| = 2$ then there are endomorphisms $f$ with invariant subspaces that are characteristic but not hyperinvariant. In this paper we give a new proof of a theorem of Shoda, which provides a necessary and sufficient condition for the existence of characteristic non-hyperinvariant subspaces.

math.RA↗
arXiv2016

Characteristic subspaces and hyperinvariant frames

Let $f$ be an endomorphism of a finite dimensional vector space $V$ over a field $K$. An $f$-invariant subspace of $V$ is called hyperinvariant (respectively characteristic) if it is invariant under all endomorphisms (respectively automorphisms) that commute with $f$. We assume $|K| = 2$, since all characteristic subspaces are hyperinvariant if $|K| > 2$. The hyperinvariant hull $W^h$ of a subspace $ W$ of $ V$ is defined to be the smallest hyperinvariant subspace of $V$ that contains $ W$, the hyperinvariant kernel $W_H$ of $ W$ is the largest hyperinvariant subspace of $V$ that is contained in $W$, and the pair $( W_H, W^h) $ is the hyperinvariant frame of $W$. In this paper we study hyperinvariant frames of characteristic non-hyperinvariant subspaces $W$. We show that all invariant subspaces in the interval $[ W_H, W^h ]$ are characteristic. We use this result for the construction of characteristic non-hyperinvariant subspaces.

math.RA↗
arXiv2015

Hyperinvariant subspaces of locally nilpotent linear transformations

A subspace $X$ of a vector space over a field $K$ is hyperinvariant with respect to an endomorphism $f$ of $V$ if it is invariant for all endomorphisms of $V$ that commute with $f$. We assume that $f$ is locally nilpotent, that is, every $ x \in V $ is annihilated by some power of $f$, and that $V$ is an infinite direct sum of $f$-cyclic subspaces. In this note we describe the lattice of hyperinvariant subspaces of $V$. We extend results of Fillmore, Herrero and Longstaff (Linear Algebra Appl. 17 (1977), 125--132) to infinite dimensional spaces.

math.RA↗
arXiv2014

Linear transformations with characteristic subspaces that are not hyperinvariant

If $f$ is an endomorphism of a finite dimensional vector space over a field $K$ then an invariant subspace $X \subseteq V$ is called hyperinvariant (respectively, characteristic) if $X$ is invariant under all endomorphisms (respectively, automorphisms) that commute with $f$. According to Shoda (Math. Zeit. 31, 611--624, 1930) only if $|K| = 2$ then there exist endomorphisms $f$ with invariant subspaces that are characteristic but not hyperinvariant. In this paper we obtain a description of the set of all characteristic non-hyperinvariant subspaces for nilpotent maps $f$ with exactly two unrepeated elementary divisors.

math.RA↗
arXiv2010

Minimal Prime Ideals of Ore Extensions over Commutative Dedekind Domains

Let R = D[x;σ;δ] be an Ore extension over a commutative Dedekind domain D, where σis an automorphism on D. In the case δ= 0 Marubayashi et. al. already investigated the class of minimal prime ideals in term of their contraction on the coefficient ring D. In this note we extend this result to a general case δnot 0.

math.RA↗