# 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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