Near-MDS Codes from Maximal Arcs in PG(2,q)
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The singleton defect of an [n,k,d] linear code C is defined as s( C)=n-k+1-d. Codes with S( C)=0 are called maximum distance separable (MDS) codes, and codes with S( C)=S( C ^)=1 are called near maximum distance separable (NMDS) codes. Both MDS codes and NMDS codes have good representations in finite projective geometry. MDS codes over F_q with length n and n-arcs in PG(k-1,q) are equivalent objects. When k=3, NMDS codes of length n are equivalent to (n,3)-arcs in PG(2,q). In this paper, we deal with the NMDS codes with dimension 3. By adding some suitable projective points in maximal arcs of PG(2,q), we can obtain two classes of (q+5,3)-arcs (or equivalently [q+5,3,q+2] NMDS codes) for any prime power q. We also determine the exact weight distribution and the locality of such NMDS codes and their duals. It turns out that the resultant NMDS codes and their duals are both distance-optimal and dimension-optimal locally recoverable codes.
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