Searcharxiv⌕ Search

arXiv subjects

Swati Bhardwaj

Publications and source records attributed to Swati Bhardwaj.

6 recordsLinked to original sources
arXiv2024

Positive values of non-homogeneous quadratic forms of type (1,4): A conjecture of Bambah, Dumir and Hans-Gill

Let $Q(x_1, \cdots,x_n)$ be a real indefinite quadratic form of the type $(r,s)$, $n=r+s$, signature $σ=r-s$ and determinant $D\neq 0$. Let $Γ_{r,n-r}$ denote the infimum of all numbers $Γ$ such that for any real numbers $c_1, c_2 ,\cdots, c_n$ there exist integers $x_1, x_ 2,\cdots, x_n$ satisfying $$0< Q(x_1+c_1,x_2+c_2,\cdots,x_n+c_n)\leq (Γ|D|)^{1/n}.$$ All the values of $Γ_{r,n-r}$ are known except for $Γ_{1,4}$. Earlier it was shown that $8\leq Γ_{1,4}<12$. It is conjectured that $Γ_{1,4}=8$. Here we shall prove that $Γ_{1,4}=8$, when (i) $c_2 \not \equiv 0 \pmod 1$, (ii) $c_2 \equiv 0 \pmod 1$, $a\geq \frac{1}{2}$, where $a$ is minima of positive definite ternary quadratic forms with determinant $4|D|$, and (iii) in some cases of $c_2 \equiv 0 \pmod 1$, $a< \frac{1}{2}$. We also obtain six critical forms for which the constant 8 is attained. In the remaining cases we prove that $Γ_{1,4}< \frac{32}{3}$.

math.NT↗
arXiv2022

New Quantum codes from constacyclic codes over a general non-chain ring

Let $q$ be a prime power and let $\mathcal{R}=\mathbb{F}_{q}[u_1,u_2, \cdots, u_k]/\langle f_i(u_i),u_iu_j-u_ju_i\rangle$ be a finite non-chain ring, where $f_i(u_i), 1\leq i \leq k$ are polynomials, not all linear, which split into distinct linear factors over $\mathbb{F}_{q}$. We characterize constacyclic codes over the ring $\mathcal{R}$ and study quantum codes from these. As an application, some new and better quantum codes, as compared to the best known codes, are obtained. We also prove that the choice of the polynomials $f_i(u_i),$ $1 \leq i \leq k$ is irrelevant while constructing quantum codes from constacyclic codes over $\mathcal{R}$, it depends only on their degrees. It is shown that there always exists Quantum MDS code $[[n,n-2,2]]_q$ for any $n$ with $\gcd (n,q)\neq 1.$

cs.IT↗
arXiv2022

Multi-dimensional Constacyclic Codes of Arbitrary Length over Finite Fields

Multi-dimensional cyclic code is a natural generalization of cyclic code. In an earlier paper we explored two-dimensional constacyclic codes over finite fields. Following the same technique, here we characterize the algebraic structure of multi-dimensional constacyclic codes, in particular three-dimensional $(α,β,γ)$- constacyclic codes of arbitrary length $s\ell k$ and their duals over a finite field $\mathbb{F}_q$, where $α,β,γ$ are non zero elements of $\mathbb{F}_q$. We give necessary and sufficient conditions for a three-dimensional $(α,β,γ)$- constacyclic code to be self-dual.

cs.IT↗
arXiv2020

Two Dimensional $\left( α,β\right) $-Constacyclic Codes of arbitrary length over a Finite Field

In this paper we characterize the algebraic structure of two-dimensional $(α,β)$-constacyclic codes of arbitrary length $s.\ell$ and of their duals. For $α,β\in \{1,-1\}$, we give necessary and sufficient conditions for a two-dimensional $(α,β)$-constacyclic code to be self-dual. We also show that a two-dimensional $(α,1 )$-constacyclic code $\mathcal{C}$ of length $n=s.\ell$ can not be self-dual if $\gcd(s,q)= 1$. Finally, we give some examples of self-dual, isodual, MDS and quasi-twisted codes corresponding to two-dimensional $(α,β)$-constacyclic codes.

cs.IT↗
arXiv2019

Skew constacyclic codes over a non-chain ring $\mathbb{F}_{q}[u,v]/\langle f(u),g(v), uv-vu\rangle$

Let $f(u)$ and $g(v)$ be two polynomials of degree $k$ and $\ell$ respectively, not both linear, which split into distinct linear factors over $\mathbb{F}_{q}$. Let $\mathcal{R}=\mathbb{F}_{q}[u,v]/\langle f(u),g(v),\\uv-vu\rangle$ be a finite commutative non-chain ring. In this paper, we study $ψ$-skew cyclic and $θ_t$-skew constacyclic codes over the ring $\mathcal{R}$ where $ψ$ and $θ_t$ are two automorphisms defined on $\mathcal{R}$.

cs.IT↗