Department of Computer Science | Institute of Theoretical Computer Science | CADMO

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: Thursday, April 30, 2009, 12:15 pm

Duration: This information is not available in the database

Location: CAB G51

Speaker: Bernd Gärtner

K-Matrix Linear Complementarity Problems and Unique Sink Orientations

The linear complementarity problem (LCP) is the following: given a square matrix M and a vector q, find nonnegative vectors w and z such that w - Mz = q and w^T z = 0. The question whether such w and z exist is NP-complete in general. If M is a P-matrix (all principal minors are positive), there are unique solution vectors w and z, but the computational complexity of finding them is unknown.

On a combinatorial level, the P-matrix LCP can be studied using the concept of unique sink orientations of cubes (USO). Recent research has focused on the translation of algebraic properties of the matrix M into combinatorial properties of the underlying USO. We will report on one result along these lines. If M is a K-matrix (a P-matrix such that all off-diagonal entries are nonpositive), the underlying USO contains short directed paths only. This generalizes (and at the same time combinatorially explains) the known result that K-matrix LCPs are polynomial-time solvable.

Joint work with Jan Foniok, Komei Fukuda and Hans-Jakob Lüthi.

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