Publications (3)0 Total impact
-
[show abstract]
[hide abstract]
ABSTRACT: In the graph avoidance game two players alternatingly color edges of a graph G in red and in blue respectively. The player who first creates a monochromatic subgraph isomorphic to a forbidden graph F loses. A symmetric strategy of the second player ensures that, independently of the first player's strategy, the blue and the red subgraph are isomorphic after every round of the game. We address the class of those graphs G that admit a symmetric strategy for all F and discuss relevant graph-theoretic and complexity issues.
11/2001;
-
[show abstract]
[hide abstract]
ABSTRACT: Generating high-quality schedules for a rotating workforce is a critical task in all settings where a certain staffing level must be guaranteed beyond the capacity of single employees, such as for instance in industrial plants, hospitals, or airline companies. Results from ergonomics [2] indicate that rotating workforce schedules have a profound impact on the health and social life of employees as well as on their performance at work. Moreover, rotating workforce schedules must satisfy legal requirements and should also meet the objectives of the employing organization. We describe our solution to this problem. A basic design decision was to aim at quickly obtaining high-quality schedules for realistically sized problems while maintaining human control. The interaction between the decision maker and the algorithm therefore consists in four steps: (1) choosing a set of lengths of work blocks (a work block is a sequence of consecutive days of work shifts), (2) choosing a particular sequence of work and days-off blocks among those that have optimal weekend characteristics, (3) enumerating possible shift sequences for the chosen work blocks subject to shift change constraints and bounds on sequences of shifts, and (4) assignment of shift sequences to work blocks while fulfilling the staffing requirements. The combination of constraint satisfaction and problem-oriented intelligent backtracking algorithms in each of the four steps allows to find good solutions for real-world problems in acceptable time.
04/2001;
-
[show abstract]
[hide abstract]
ABSTRACT: . Part One of this report is a presentation of known results in the areas of logic and complexity theory written in an intuitive style and presents a number of examples. Among other things several non-monotonic formalisms which can be used for knowledge representation in artificial intelligence and their relationship to each other are discussed. The ample second part consists of a large variety of complexity results for model checking of non-monotonic formalisms and for determining a belief pair of a three-valued semantics of autoepistemic logic. Model Checking is the question whether a given interpretation satisfies a theory (in this case a non-monotonic theory) and is a viable alternative to reasoning. A number of open complexity problems for model checking with default logic and with default logic with weak extensions is solved; for instance it is shown that model checking with normal default theories is P 2 -complete, however in the case of weak extensions P 2 -c...
10/2000;
