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Hankel Rhotrices And Constructions Of Maximum Distance Separable Rhotrices Over Finite Fields, P. L. Sharma, Arun Kumar, Shalini Gupta Dec 2019

Hankel Rhotrices And Constructions Of Maximum Distance Separable Rhotrices Over Finite Fields, P. L. Sharma, Arun Kumar, Shalini Gupta

Applications and Applied Mathematics: An International Journal (AAM)

Many block ciphers in cryptography use Maximum Distance Separable (MDS) matrices to strengthen the diffusion layer. Rhotrices are represented by coupled matrices. Therefore, use of rhotrices in the cryptographic ciphers doubled the security of the cryptosystem. We define Hankel rhotrix and further construct the maximum distance separable rhotrices over finite fields.


The Matrix-Valued Numerical Range Over Finite Fields, Edoardo Ballico Jan 2019

The Matrix-Valued Numerical Range Over Finite Fields, Edoardo Ballico

Turkish Journal of Mathematics

In this paper we define and study the matrix-valued $k\times k$ numerical range of $n\times n$ matrices using the Hermitian product and the product with $n\times k$ unitary matrices $U$ (on the right with $U$, on the left with its adjoint $U^\dagger = U^{-1}$). For all $i, j=1,\dots ,k$ we study the possible $(i,j)$-entries of these $k\times k$ matrices. Our results are for the case in which the base field is finite, but the same definition works over $\mathbb {C}$. Instead of the degree $2$ extension $\mathbb {R}\hookrightarrow \mathbb {C}$ we use the degree $2$ extension $\mathbb {F} _q\hookrightarrow \mathbb …


The Numerical Range Of Matrices Over $\Mathbb {F}_4$, Edoardo Ballico Jan 2019

The Numerical Range Of Matrices Over $\Mathbb {F}_4$, Edoardo Ballico

Turkish Journal of Mathematics

For any prime power $q$ and any $u = (x_1,\dots ,x_n),v = (y_1,\dots ,y_n)\in \mathbb {F} _{q^2}^n$ set $\langle u,v\rangle := \sum _{i=1}^{n} x_i^qy_i$. For any $k\in \mathbb {F} _q$ and any $n\times n$ matrix $M$ over $\mathbb {F} _{q^2}$, the $k$-numerical range $\mathrm{Num} _k(M)$ of $M$ is the set of all $\langle u,Mu\rangle$ for $u\in \mathbb {F} _{q^2}^n$ with $\langle u,u\rangle =k$ \cite{cjklr}. Here, we study the case $q=2$, which is quite different from the case $q\ne 2$.