<p>Let <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2145_Article_IEq1.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="66" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{Sym}_q(m)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mtext>Sym</mtext> <mi>q</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>m</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> be the space of symmetric matrices in <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2145_Article_IEq2.gif" Format="GIF" Height="22" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathbb {F}}_q^{m\times m}\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi mathvariant="double-struck">F</mi> <mi>q</mi> <mrow> <mi>m</mi> <mo>×</mo> <mi>m</mi> </mrow> </msubsup> </math></EquationSource> </InlineEquation>. A subspace of <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2145_Article_IEq1.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="66" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{Sym}_q(m)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mtext>Sym</mtext> <mi>q</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>m</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> equipped with the rank distance is called an <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2145_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\({{\mathbb {F}}}_{q}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="double-struck">F</mi> <mi>q</mi> </msub> </math></EquationSource> </InlineEquation>-linear symmetric rank-metric code. In this paper, we study the covering properties of <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2145_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\({{\mathbb {F}}}_{q}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="double-struck">F</mi> <mi>q</mi> </msub> </math></EquationSource> </InlineEquation>-linear symmetric rank-metric codes. First we characterize <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2145_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\({{\mathbb {F}}}_{q}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="double-struck">F</mi> <mi>q</mi> </msub> </math></EquationSource> </InlineEquation>-linear symmetric rank-metric codes which are perfect, i.e., that satisfy the equality in the sphere-packing like bound. We show that, despite the rank-metric case, there are non-trivial perfect codes. Indeed, we prove that the only perfect non-trivial <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2145_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\({{\mathbb {F}}}_{q}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="double-struck">F</mi> <mi>q</mi> </msub> </math></EquationSource> </InlineEquation>-linear symmetric rank-metric codes in <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2145_Article_IEq1.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="66" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{Sym}_q(m)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mtext>Sym</mtext> <mi>q</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>m</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> are the symmetric MRD codes with minimum distance 3 and <i>m</i> odd. Also, we characterize families of codes which are quasi-perfect.</p>

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On perfect symmetric rank-metric codes

  • Usman Mushrraf,
  • Ferdinando Zullo

摘要

Let \(\textrm{Sym}_q(m)\) Sym q ( m ) be the space of symmetric matrices in \({\mathbb {F}}_q^{m\times m}\) F q m × m . A subspace of \(\textrm{Sym}_q(m)\) Sym q ( m ) equipped with the rank distance is called an \({{\mathbb {F}}}_{q}\) F q -linear symmetric rank-metric code. In this paper, we study the covering properties of \({{\mathbb {F}}}_{q}\) F q -linear symmetric rank-metric codes. First we characterize \({{\mathbb {F}}}_{q}\) F q -linear symmetric rank-metric codes which are perfect, i.e., that satisfy the equality in the sphere-packing like bound. We show that, despite the rank-metric case, there are non-trivial perfect codes. Indeed, we prove that the only perfect non-trivial \({{\mathbb {F}}}_{q}\) F q -linear symmetric rank-metric codes in \(\textrm{Sym}_q(m)\) Sym q ( m ) are the symmetric MRD codes with minimum distance 3 and m odd. Also, we characterize families of codes which are quasi-perfect.