Permutation Inequalities for Walks in Graphs

Using spectral graph theory, we show how to obtain inequalities for the number of walks in graphs from nonnegative polynomials and present a new family of such inequalities

Densities of Codes of Various Linearity Degrees in Translation-Invariant Metric Spaces

We investigate the asymptotic density of error-correcting codes with good distance properties and prescribed linearity degree, including sublinear and nonlinear codes. We focus on the general setting of finite translation-invariant metric spaces, and then specialize our results to the Hamming metric, to the rank metric, and to the sum-rank metric. Our results show that the asymptotic density of codes heavily depends on the imposed linearity degree and the chosen metric

On the Number of tt-Lee-Error-Correcting Codes

We consider $t$-Lee-error-correcting codes of length $n$ over the residue ring $\mathbb{Z}_m := \mathbb{Z}/m\mathbb{Z}$ and determine upper and lower bounds on the number of $t$-Lee-error-correcting codes. We use two different methods, namely estimating isolated nodes on bipartite graphs and the graph container method. The former gives density results for codes of fixed size and the latter for any size. This confirms some recent density results for linear Lee metric codes and provides new density results for nonlinear codes. To apply a variant of the graph container algorithm we also investigate some geometrical properties of the balls in the Lee metric

Dihedral Quantum Codes

We study dihedral quantum codes of short block length, a large class of quantum CSS codes obtained by the lifted product construction. We present code construction and give a formula for the code dimension, depending on the two classical codes on which the CSS code is based on. We also give a lower bound on the code distance. Finally we construct an example of short dihedral quantum codes, improving parameters of previously known quantum codes