Equality conjecture for linkage construction bounds

Let qq be a prime power, and let Bq(v1,v2,d;k)B_q(v_1,v_2,d;k) denote the maximum size of a constant-dimension code in a v1v_1-dimensional vector space whose codewords have dimension kk, minimum subspace distance dd, and intersect a fixed v2v_2-dimensional subspace in dimension at least d/2d/2. Let Aq(n,d;k)A_q(n,d;k) denote the maximum size of a constant-dimension code with ambient dimension nn, codeword dimension kk, and minimum subspace distance dd. Equality conjecture for linkage construction bounds. If v1v2+2k+1v_1\ge v_2+2\ge k+1 and k3k\ge 3, then

Bq(v1,v2,2k2;k)=Aq(v2,2k4;k1).B_q(v_1,v_2,2k-2;k)=A_q(v_2,2k-4;k-1).

This conjectures that the lower bound produced by the linkage construction is sharp in the indicated parameter range, giving an exact value for BqB_q. The claim is presented as a conjecture based on computational trials and heuristic construction; its resolution is not established in the supplied text.

Sources & referencesView supporting material

Primary source

Sascha Kurz, “A note on the linkage construction for constant dimension codes”, arXiv:1906.09780 (2020).

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