## Theory of Combinatorial Algorithms

Prof. Emo Welzl and Prof. Bernd Gärtner

# Mittagsseminar (in cooperation with M. Ghaffari, A. Steger and B. Sudakov)

 Mittagsseminar Talk Information

Date and Time: Tuesday, July 22, 2008, 12:15 pm

Duration: This information is not available in the database

Location: CAB G51

Speaker: Jeong Han Kim (Yonsei Univ., South Korea)

## Optimal Query Complexity Bounds for Finding Graphs

We consider the problem of finding an unknown graph by using two types of queries with an additive property. Given a graph, an additive query asks the number of edges in a set of vertices while a cross-additive query asks the number of edges crossing between two disjoint sets of vertices. The queries ask sum of weights for the weighted graphs. These types of queries were partially motivated in DNA shotgun sequencing and linkage discovery problem of artificial intelligence.

For a given unknown weighted graph $G$ with $n$ vertices, $m$ edges, and a certain mild condition on weights, we prove that there exists a non-adaptive algorithm to find the edges of $G$ using $O\left(\frac{m\log{n}}{\log{m}}\right)$ queries of both types provided that $m \geq n^{\epsilon}$ for any constant $\epsilon> 0$. For a graph, it is shown that the same bound holds for all range of $m$.

This settles a conjecture of Grebinski for finding an unweighted graph using additive queries. We also consider the problem of finding the Fourier coefficients of a certain class of pseudo-Boolean functions. A similar coin weighing problem is also considered.

Joint work with S. Choi.

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