# American Institute of Mathematical Sciences

May  2011, 5(2): 161-176. doi: 10.3934/amc.2011.5.161

## On $q$-analogs of Steiner systems and covering designs

 1 Computer Science Department, Technion - Israel Institute of Technology, Haifa, 32000, Israel 2 Department of Electrical and Computer Engineering, Department of Computer Science and Engineering, Department of Mathematics, University of California San Diego, 9500 Gilman Drive, La Jolla, CA92093, United States

Received  March 2010 Revised  October 2010 Published  May 2011

The $q$-analogs of covering designs, Steiner systems, and Turán designs are studied. It is shown that $q$-covering designs and $q$-Turán designs are dual notions. A strong necessary condition for the existence of Steiner structures (the $q$-analogs of Steiner systems) over $\mathbb F$2 is given. No Steiner structures of strength $2$ or more are currently known, and our condition shows that their existence would imply the existence of new Steiner systems of strength $3$. The exact values of the $q$-covering numbers $\mathcal C$q$(n,k,1)$ and $\mathcal C$q$(n,n-1,r)$ are determined for all $q,n,k,r$. Furthermore, recursive upper and lower bounds on the size of general $q$-covering designs and $q$-Turán designs are presented. Finally, it is proved that $\mathcal C$2$(5,3,2) = 27$ and $\mathcal C$2$(7,3,2) \leq 399$. Tables of upper and lower bounds on $\mathcal C$2$(n,k,r)$ are given for all $n \leq 8$.
Citation: Tuvi Etzion, Alexander Vardy. On $q$-analogs of Steiner systems and covering designs. Advances in Mathematics of Communications, 2011, 5 (2) : 161-176. doi: 10.3934/amc.2011.5.161
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##### References:
 [1] R. Ahlswede, H. K. Aydinian and L. H. Khachatrian, On perfect codes and related concepts,, Des. Codes Crypt., 22 (2001), 221.  doi: 10.1023/A:1008394205999.  Google Scholar [2] M. Braun, A. Kerber and R. Laue, Systematic construction of $q$-analogs of $t$-$(v,k,\lambda)$-designs,, Des. Codes Crypt., 34 (2005), 55.  doi: 10.1007/s10623-003-4194-z.  Google Scholar [3] T. Bu, Partitions of a vector space,, Disc. Math., 31 (1980), 79.  doi: 10.1016/0012-365X(80)90174-0.  Google Scholar [4] D. de Caen, Extension of a theorem of Moon and Moser on complete subgraphs,, Ars Combinatoria, 16 (1983), 5.   Google Scholar [5] D. de Caen, The current status of Turán's problem on hypergraphs,, in, (1991), 187.   Google Scholar [6] C. J. Colbourn and R. Mathon, Steiner systems,, in, (2007), 102.   Google Scholar [7] T. Etzion, Perfect byte-correcting codes,, IEEE Trans. Inform. Theory, 44 (1998), 3140.  doi: 10.1109/18.737544.  Google Scholar [8] T. Etzion and A. Vardy, Error-correcting codes in projective space,, IEEE Trans. Inform. Theory, 57 (2011), 1165.  doi: 10.1109/TIT.2010.2095232.  Google Scholar [9] S. J. Hong and A. M. Patel, A general class of maximal codes for computer applications,, IEEE Trans. Comput., 21 (1972), 1322.  doi: 10.1109/T-C.1972.223503.  Google Scholar [10] T. Itoh, A new family of $2$-designs over GF$(q)$ admitting SLm$(q^l)$,, Geom. Dedicata, 69 (1998), 261.  doi: 10.1023/A:1005057610394.  Google Scholar [11] R. Koetter and F. R. Kschischang, Coding for errors and erasures in random network coding,, IEEE Trans. Inform. Theory, 54 (2008), 3579.  doi: 10.1109/TIT.2008.926449.  Google Scholar [12] A. Kohnert and S. Kurz, Construction of large constant dimension codes with a prescribed minimum distance,, Lect. Notes Comput. Sci., 5393 (2008), 31.  doi: 10.1007/978-3-540-89994-5_4.  Google Scholar [13] J. H. van Lint and R. M. Wilson, "A Course in Combinatorics,'', Cambridge University Press, (1992).   Google Scholar [14] M. Miyakawa, A. Munemasa and S. Yoshiara, On a class of small $2$-designs over GF$(q)$,, J. Combin. Des., 3 (1995), 61.  doi: 10.1002/jcd.3180030108.  Google Scholar [15] J. Schönheim, On coverings,, Pacific J. Math., 14 (1964), 1405.   Google Scholar [16] M. Schwartz and T. Etzion, Codes and anticodes in the Grassman graph,, J. Combin. Theory Ser. A, 97 (2002), 27.  doi: 10.1006/jcta.2001.3188.  Google Scholar [17] H. Suzuki, $2$-designs over GF$(2^m)$,, Graphs Combin., 6 (1990), 293.  doi: 10.1007/BF01787580.  Google Scholar [18] H. Suzuki, $2$-designs over GF$(q)$,, Graphs Combin., 8 (1992), 381.  doi: 10.1007/BF02351594.  Google Scholar [19] S. Thomas, Designs over finite fields,, Geom. Dedicata, 21 (1987), 237.   Google Scholar [20] S. Thomas, Designs and partial geometries over finite fields,, Geom. Ded., 63 (1996), 247.  doi: 10.1007/BF00181415.  Google Scholar
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