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Register a new userIndependent Spaces of q-Polymatroids
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Added by
Heide Gluesing-Luerssen
Publication date
2021
fields
Informatics Engineering
and research's language is
English
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This paper is devoted to the study of independent spaces of q-polymatroids. With the aid of an auxiliary q-matroid it is shown that the collection of independent spaces satisfies the same properties as for q-matroids. However, in contrast to q-matroids, the rank value of an independent space does not agree with its dimension. Nonetheless, the rank values of the independent spaces fully determine the q-polymatroid, and this fact can be exploited to derive a cryptomorphism of q-polymatroids. Finally, the notions of minimal spanning spaces, maximally strongly independent spaces, and bases will be elaborated on.
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The Assmus-Mattson theorem gives a way to identify block designs arising from codes. This result was broadened to matroids and weighted designs. In this work we present a further two-fold generalisation: first from matroids to polymatroids and also from sets to vector spaces. To achieve this, we introduce the characteristic polynomial of a $q$-polymatroid and outline several of its properties.
It is well known that linear rank-metric codes give rise to $q$-polymatroids. Analogously to classical matroid theory one may ask whether a given $q$-polymatroid is representable by a rank-metric code. We provide a partial answer by presenting examples of $q$-matroids that are not representable by ${mathbb F}_{q^m}$-linear rank-metric codes. We then go on and introduce deletion and contraction for $q$-polymatroids and show that they are mutually dual and that they correspond to puncturing and shortening of rank-metric codes. Finally, we introduce a closure operator along with the notion of flats and show that the generalized rank weights of a rank-metric code are fully determined by the flats of the associated $q$-polymatroid.
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