Abstract

The maximum size $A_2(8,6;4)$ of a binary subspace code of packet length $v=8$, minimum subspace distance $d=6$, and constant dimension $k=4$ is $257$, where the $2$ isomorphism types are extended lifted maximum rank distance codes. In finite geometry terms the maximum number of solids in $\operatorname{PG}(7,2)$, mutually intersecting in at most a point, is $257$. The result was obtained by combining the classification of substructures with integer linear programming techniques. This implies that the maximum size $A_2(8,6)$ of a binary mixed-dimension code of packet length $8$ and minimum subspace distance $6$ is $257$ as well.

Highlights

  • Let q be a prime power, Fq be the field with q elements, and V ∼= Fvq a v-dimensional vector space over Fq

  • By L(V ) we denote the set of all subspaces of V, or flats of the projective geometry PG(V ) ∼= PG(Fvq ) =: PG(v − 1, q)

  • It forms a metric space with respect to the subspace distance ds(U, W ) := dim(U + W ) − dim(U ∩ W ) = dim(U ) + dim(W ) − 2 dim(U ∩ W ) and may be viewed as a q-analogue of the Hamming space (Fv2, dHam)

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Summary

Introduction

Let q be a prime power, Fq be the field with q elements, and V ∼= Fvq a v-dimensional vector space over Fq. As in [14], we want to apply integer linear programming methods in order to determine the exact maximum size of CDCs with the specified parameters. Since this algorithmic approach suffers from the presence of a large symmetry group, we use the inherent symmetry to prescribe some carefully chosen substructures up to isomorphism.

Preliminaries
Integer linear programming models
Proof of the main theorem
Excluding hyperplane configurations
Extending hyperplane configurations to 31-point-hyperplane configurations
Excluding hyperplane configurations to 31-point-hyperplane configurations

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