Article Contents
Article Contents

# Some results on the structure of constacyclic codes and new linear codes over GF(7) from quasi-twisted codes

The work of the first two authors is supported by Kenyon College Summer Science Scholars program

• One of the most important and challenging problems in coding theory is to construct codes with good parameters. There are various methods to construct codes with the best possible parameters. A promising and fruitful approach has been to focus on the class of quasi-twisted (QT) codes which includes constacyclic codes as a special case. This class of codes is known to contain many codes with good parameters. Although constacyclic codes and QT codes have been the subject of numerous studies and computer searches over the last few decades, we have been able to discover a new fundamental result about the structure of constacyclic codes which was instrumental in our comprehensive search method for new QT codes over GF(7). We have been able to find 41 QT codes with better parameters than the previously best known linear codes. Furthermore, we derived a number of additional new codes via Construction X as well as standard constructions, such as shortening and puncturing.

Mathematics Subject Classification: Primary: 94B65; Secondary: 11T71.

 Citation:

• Table 1.  Shift constants $a$ and lengths $n$ of constacyclic codes to be examined for each finite field $q=3, 4, 5, 7, 8, 9, 11, 13$, where $\alpha\in GF(9)$ is a root of $x^2+2x+2$.

 $q$ $a\neq0, 1$ $n$ maximum $n$ 3 2 all $n=2m$ 243 4 any field element all $n=3m$ 256 5 2 all $n=2m$ 130 4 all $n=4m$ 7 2 all $n=3m$ 100 3 all $n=2m$ or $n=3m$ 6 all $n=2m$ 8 any field element all $n=7m$ 130 9 $\alpha$ all $n=2m$ 130 $\alpha^2$ all $n=4m$ $\alpha^4$ all $n=8m$ 11 2 all $n=2m$ or $n=5m$ 150 3 all $n=5m$ 10 all $n=2m$ 13 2 all $n=2m$ or $n=3m$ 150 3 all $n=3m$ 4 all $n=3m$ or $n=4m$ 5 all $n=2m$ 12 all $n=4m$
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