{"title":"Optimal $$(r,delta )$$ -LRCs from monomial-Cartesian codes and their subfield-subcodes","authors":"C. Galindo, F. Hernando, H. Martín-Cruz","doi":"10.1007/s10623-024-01403-z","DOIUrl":"https://doi.org/10.1007/s10623-024-01403-z","url":null,"abstract":"<p>We study monomial-Cartesian codes (MCCs) which can be regarded as <span>((r,delta ))</span>-locally recoverable codes (LRCs). These codes come with a natural bound for their minimum distance and we determine those giving rise to <span>((r,delta ))</span>-optimal LRCs for that distance, which are in fact <span>((r,delta ))</span>-optimal. A large subfamily of MCCs admits subfield-subcodes with the same parameters of certain optimal MCCs but over smaller supporting fields. This fact allows us to determine infinitely many sets of new <span>((r,delta ))</span>-optimal LRCs and their parameters.</p>","PeriodicalId":11130,"journal":{"name":"Designs, Codes and Cryptography","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140890376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Computing gluing and splitting $$(ell ,ell )$$ -isogenies","authors":"Song Tian","doi":"10.1007/s10623-024-01413-x","DOIUrl":"https://doi.org/10.1007/s10623-024-01413-x","url":null,"abstract":"<p>We give algorithms to compute <span>((ell ,ell ))</span>-isogenies between Jacobians of genus 2 curves and products of elliptic curves in time of <span>({tilde{O}}(ell ^2))</span> basic field operations, where <span>(ell )</span> is an odd prime different from the characteristic of the field. The method relies on the notion of a normal Weil set of Weil functions due to Shepherd-Barron, and works for the case of computing <span>((ell ,ell ))</span>-isogenies between Jacobians of genus 2 curves.</p>","PeriodicalId":11130,"journal":{"name":"Designs, Codes and Cryptography","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140890398","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Characterization of weakly regular p-ary bent functions of $$ell $$ -form","authors":"Jong Yoon Hyun, Jungyun Lee, Yoonjin Lee","doi":"10.1007/s10623-024-01411-z","DOIUrl":"https://doi.org/10.1007/s10623-024-01411-z","url":null,"abstract":"<p>We study the essential properties of weakly regular <i>p</i>-ary bent functions of <span>(ell )</span>-form, where a <i>p</i>-ary function is from <span>(mathbb {F}_{p^m})</span> to <span>(mathbb {F}_p)</span>. We observe that most of studies on a weakly regular <i>p</i>-ary bent function <i>f</i> with <span>(f(0)=0)</span> of <span>(ell )</span>-form always assume the <i>gcd-condition</i>: <span>(gcd (ell -1,p-1)=1)</span>. We first show that whenever considering weakly regular <i>p</i>-ary bent functions <i>f</i> with <span>(f(0) = 0)</span> of <span>(ell )</span>-form, we can drop the gcd-condition; using the gcd-condition, we also obtain a characterization of a weakly regular bent function of <span>(ell )</span>-form. Furthermore, we find an additional characterization for weakly regular bent functions of <span>(ell )</span>-form; we consider two cases <i>m</i> being even or odd. Let <i>f</i> be a weakly regular bent function of <span>(ell )</span>-form preserving the zero element; then in the case that <i>m</i> is odd, we show that <i>f</i> satisfies <span>(gcd (ell ,p-1)=2)</span>. On the other hand, when <i>m</i> is even and <i>f</i> is also non-regular, we show that <i>f</i> satisfies <span>(gcd (ell ,p-1)=2)</span> as well. In addition, we present two explicit families of regular bent functions of <span>(ell )</span>-form in terms of the gcd-condition.</p>","PeriodicalId":11130,"journal":{"name":"Designs, Codes and Cryptography","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140890399","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On the packing density of Lee spheres","authors":"Ang Xiao, Yue Zhou","doi":"10.1007/s10623-024-01410-0","DOIUrl":"https://doi.org/10.1007/s10623-024-01410-0","url":null,"abstract":"<p>Based on the packing density of cross-polytopes in <span>({mathbb {R}}^n)</span>, more than 50 years ago Golomb and Welch proved that the packing density of Lee spheres in <span>({mathbb {Z}}^n)</span> must be strictly smaller than 1 provided that the radius <i>r</i> of the Lee sphere is large enough compared with <i>n</i>, which implies that there is no perfect Lee code for the corresponding parameters <i>r</i> and <i>n</i>. In this paper, we investigate the lattice packing density of Lee spheres with fixed radius <i>r</i> for infinitely many <i>n</i>. First we present a method to verify the nonexistence of the second densest lattice packing of Lee spheres of radius 2. Second, we consider the constructions of lattice packings with density <span>(delta _nrightarrow frac{2^r}{(2r+1)r!})</span> as <span>(nrightarrow infty )</span>. When <span>(r=2)</span>, the packing density can be improved to <span>(delta _nrightarrow frac{2}{3})</span> as <span>(nrightarrow infty )</span>.</p>","PeriodicalId":11130,"journal":{"name":"Designs, Codes and Cryptography","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140817605","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Subgroup total perfect codes in Cayley sum graphs","authors":"Xiaomeng Wang, Lina Wei, Shou-Jun Xu, Sanming Zhou","doi":"10.1007/s10623-024-01405-x","DOIUrl":"https://doi.org/10.1007/s10623-024-01405-x","url":null,"abstract":"<p>Let <span>(Gamma )</span> be a graph with vertex set <i>V</i>, and let <i>a</i>, <i>b</i> be nonnegative integers. An (<i>a</i>, <i>b</i>)-regular set in <span>(Gamma )</span> is a nonempty proper subset <i>D</i> of <i>V</i> such that every vertex in <i>D</i> has exactly <i>a</i> neighbours in <i>D</i> and every vertex in <span>(V setminus D)</span> has exactly <i>b</i> neighbours in <i>D</i>. In particular, a (1, 1)-regular set is called a total perfect code. Let <i>G</i> be a finite group and <i>S</i> a square-free subset of <i>G</i> closed under conjugation. The Cayley sum graph <span>(textrm{CayS}(G,S))</span> of <i>G</i> is the graph with vertex set <i>G</i> such that two vertices <i>x</i>, <i>y</i> are adjacent if and only if <span>(xy in S)</span>. A subset (respectively, subgroup) <i>D</i> of <i>G</i> is called an (<i>a</i>, <i>b</i>)-regular set (respectively, subgroup (<i>a</i>, <i>b</i>)-regular set) of <i>G</i> if there exists a Cayley sum graph of <i>G</i> which admits <i>D</i> as an (<i>a</i>, <i>b</i>)-regular set. We obtain two necessary and sufficient conditions for a subgroup of a finite group <i>G</i> to be a total perfect code in a Cayley sum graph of <i>G</i>. We also obtain two necessary and sufficient conditions for a subgroup of a finite abelian group <i>G</i> to be a total perfect code of <i>G</i>. We classify finite abelian groups whose all non-trivial subgroups of even order are total perfect codes of the group, and as a corollary we obtain that a finite abelian group has the property that every non-trivial subgroup is a total perfect code if and only if it is isomorphic to an elementary abelian 2-group. We prove that, for a subgroup <i>H</i> of a finite abelian group <i>G</i> and any pair of positive integers (<i>a</i>, <i>b</i>) within certain ranges depending on <i>H</i>, <i>H</i> is an (<i>a</i>, <i>b</i>)-regular set of <i>G</i> if and only if it is a total perfect code of <i>G</i>. Finally, we give a classification of subgroup total perfect codes of a cyclic group, a dihedral group and a generalized quaternion group.</p>","PeriodicalId":11130,"journal":{"name":"Designs, Codes and Cryptography","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2024-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140817584","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Special directions on the finite affine plane","authors":"Gergely Kiss, Gábor Somlai","doi":"10.1007/s10623-024-01404-y","DOIUrl":"https://doi.org/10.1007/s10623-024-01404-y","url":null,"abstract":"<p>In this paper we study the number of special directions of sets of cardinality divisible by <i>p</i> on a finite plane of order <i>p</i>, where <i>p</i> is a prime. We show that there is no such a set with exactly two special directions. We characterise sets with exactly three special directions which answers a question of Ghidelli in negative. Further we introduce methods to construct sets of minimal cardinality that have exactly four special directions for small values of <i>p</i>.</p>","PeriodicalId":11130,"journal":{"name":"Designs, Codes and Cryptography","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2024-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140817615","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Small weight codewords of projective geometric codes II","authors":"Sam Adriaensen, Lins Denaux","doi":"10.1007/s10623-024-01397-8","DOIUrl":"https://doi.org/10.1007/s10623-024-01397-8","url":null,"abstract":"<p>The <span>(p)</span>-ary linear code <span>(mathcal {C}_{k}!left( n,qright) )</span> is defined as the row space of the incidence matrix <span>(A)</span> of <span>(k)</span>-spaces and points of <span>(textrm{PG}!left( n,qright) )</span>. It is known that if <span>(q)</span> is square, a codeword of weight <span>(q^ksqrt{q}+mathcal {O}!left( q^{k-1}right) )</span> exists that cannot be written as a linear combination of at most <span>(sqrt{q})</span> rows of <span>(A)</span>. Over the past few decades, researchers have put a lot of effort towards proving that any codeword of smaller weight <i>does</i> meet this property. We show that if <span>(qgeqslant 32)</span> is a composite prime power, every codeword of <span>(mathcal {C}_{k}!left( n,qright) )</span> up to weight <span>(mathcal {O}!left( q^ksqrt{q}right) )</span> is a linear combination of at most <span>(sqrt{q})</span> rows of <span>(A)</span>. We also generalise this result to the codes <span>(mathcal {C}_{j,k}!left( n,qright) )</span>, which are defined as the <span>(p)</span>-ary row span of the incidence matrix of <i>k</i>-spaces and <i>j</i>-spaces, <span>(j < k)</span>.</p>","PeriodicalId":11130,"journal":{"name":"Designs, Codes and Cryptography","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2024-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140808394","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alexander A. Davydov, Stefano Marcugini, Fernanda Pambianco
{"title":"Further results on covering codes with radius R and codimension $$tR+1$$","authors":"Alexander A. Davydov, Stefano Marcugini, Fernanda Pambianco","doi":"10.1007/s10623-024-01402-0","DOIUrl":"https://doi.org/10.1007/s10623-024-01402-0","url":null,"abstract":"<p>The length function <span>(ell _q(r,R))</span> is the smallest possible length <i>n</i> of a <i>q</i>-ary linear <span>([n,n-r]_qR)</span> code with codimension (redundancy) <i>r</i> and covering radius <i>R</i>. Let <span>(s_q(N,rho ))</span> be the smallest size of a <span>(rho )</span>-saturating set in the projective space <span>(textrm{PG}(N,q))</span>. There is a one-to-one correspondence between <span>([n,n-r]_qR)</span> codes and <span>((R-1))</span>-saturating <i>n</i>-sets in <span>(textrm{PG}(r-1,q))</span> that implies <span>(ell _q(r,R)=s_q(r-1,R-1))</span>. In this work, for <span>(Rge 3)</span>, new asymptotic upper bounds on <span>(ell _q(tR+1,R))</span> are obtained in the following form: </p><span>$$begin{aligned}&bullet ~ell _q(tR+1,R) =s_q(tR,R-1)&hspace{0.4cm} le root R of {frac{R!}{R^{R-2}}}cdot q^{(r-R)/R}cdot root R of {ln q}+o(q^{(r-R)/R}), hspace{0.3cm} r=tR+1,~tge 1,&hspace{0.4cm}~ qtext { is an arbitrary prime power},~qtext { is large enough};&bullet ~text { if additionally }Rtext { is large enough, then }root R of {frac{R!}{R^{R-2}}}thicksim frac{1}{e}thickapprox 0.3679. end{aligned}$$</span><p>The new bounds are essentially better than the known ones. For <span>(t=1)</span>, a new construction of <span>((R-1))</span>-saturating sets in the projective space <span>(textrm{PG}(R,q))</span>, providing sets of small sizes, is proposed. The <span>([n,n-(R+1)]_qR)</span> codes, obtained by the construction, have minimum distance <span>(R + 1)</span>, i.e. they are almost MDS (AMDS) codes. These codes are taken as the starting ones in the lift-constructions (so-called “<span>(q^m)</span>-concatenating constructions”) for covering codes to obtain infinite families of codes with growing codimension <span>(r=tR+1)</span>, <span>(tge 1)</span>.</p>","PeriodicalId":11130,"journal":{"name":"Designs, Codes and Cryptography","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2024-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140651611","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Using $$P_tau $$ property for designing bent functions provably outside the completed Maiorana–McFarland class","authors":"Enes Pasalic, Amar Bapić, Fengrong Zhang, Yongzhuang Wei","doi":"10.1007/s10623-024-01407-9","DOIUrl":"https://doi.org/10.1007/s10623-024-01407-9","url":null,"abstract":"<p>In this article, we identify certain instances of bent functions, constructed using the so-called <span>(P_tau )</span> property, that are provably outside the completed Maiorana–McFarland (<span>({mathcal{M}mathcal{M}}^#)</span>) class. This also partially answers an open problem in posed by Kan et al. (IEEE Trans Inf Theory, https://doi.org/10.1109/TIT.2022.3140180, 2022). We show that this design framework (using the <span>(P_tau )</span> property), can provide instances of bent functions that are outside the known classes of bent functions, including the classes <span>({mathcal{M}mathcal{M}}^#)</span>, <span>({{mathcal {C}}},{{mathcal {D}}})</span> and <span>({{mathcal {D}}}_0)</span>, where the latter three were introduced by Carlet in the early nineties. We provide two generic methods for identifying such instances, where most notably one of these methods uses permutations that may admit linear structures. For the first time, a set of sufficient conditions for the functions of the form <span>(h(y,z)=Tr(ypi (z)) + G_1(Tr_1^m(alpha _1y),ldots ,Tr_1^m(alpha _ky))G_2(Tr_1^m(beta _{k+1}z),ldots ,Tr_1^m(beta _{tau }z))+ G_3(Tr_1^m(alpha _1y),ldots ,Tr_1^m(alpha _ky)))</span> to be bent and outside <span>({mathcal{M}mathcal{M}}^#)</span> is specified without a strong assumption that the components of the permutation <span>(pi )</span> do not admit linear structures.</p>","PeriodicalId":11130,"journal":{"name":"Designs, Codes and Cryptography","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140636276","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Chain-imprimitive, flag-transitive 2-designs","authors":"Carmen Amarra, Alice Devillers, Cheryl E. Praeger","doi":"10.1007/s10623-024-01400-2","DOIUrl":"https://doi.org/10.1007/s10623-024-01400-2","url":null,"abstract":"<p>We consider 2-designs which admit a group of automorphisms that is flag-transitive and leaves invariant a chain of nontrivial point-partitions. We build on our recent work on 2-designs which are block-transitive but not necessarily flag-transitive. In particular we use the concept of the “array” of a point subset with respect to the chain of point-partitions; the array describes the distribution of the points in the subset among the classes of each partition. We obtain necessary and sufficient conditions on the array in order for the subset to be a block of such a design. By explicit construction we show that for any <span>(s ge 2)</span>, there are infinitely many 2-designs admitting a flag-transitive group that preserves an invariant chain of point-partitions of length <i>s</i>. Moreover an exhaustive computer search, using <span>Magma</span>, seeking designs with <span>(e_1e_2e_3)</span> points (where each <span>(e_ile 50)</span>) and a partition chain of length <span>(s=3)</span>, produced 57 such flag-transitive designs, among which only three designs arise from our construction—so there is still much to learn.\u0000</p>","PeriodicalId":11130,"journal":{"name":"Designs, Codes and Cryptography","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2024-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140621512","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}