For some computational problems (e.g., product configuration, planning, diagnosis, query answering, phylogeny reconstruction) computing a set of similar diverse solutions may be desirable for better decision-making. With this motivation, we studied several decision optimization versions of this problem in the context of Answer Set Programming (ASP), analyzed their computational complexity, and introduced offline online methods to compute similar diverse solutions of such computational problems with respect to a given distance function. All these methods rely on the idea of computing solutions to a problem by means of finding the answer sets for an ASP program that describes the problem. The offline methods compute all solutions in advance using the ASP formulation of the problem with an ASP solver, like Clasp, and then identify similar diverse solutions using clustering methods. The online methods compute similar diverse solutions following one of the three approaches: by reformulating the ASP representation of the problem to compute similar diverse solutions at once using an ASP solver; by computing similar diverse solutions iteratively (one after other) using an ASP solver; by modifying the search algorithm of an ASP solver to compute similar diverse solutions incrementally. We modified Clasp to implement the last online method and called it Clasp-NK. In the first two online methods, the given distance function is represented in ASP; in the last one it is implemented in C++. We showed the applicability and the effectiveness of these methods on reconstruction of similar diverse phylogenies for Indo-European languages, and on several planning problems in Blocks World. We observed that in terms of computational efficiency the last online method outperforms the others; also it allows us to compute similar diverse solutions when the distance function cannot be represented in ASP.
@cite_24: In many AI fields, the problem of finding out a solution which is as close as possible to a given configuration has to be faced. This paper addresses this problem in a propositional framework. The decision problem DISTANCE-SAT that consists in determining whether a propositional CNF formula admits a model that disagrees with a given partial interpretation on at most d variables, is introduced. The complexity of DISTANCE-SAT an d of several restrictions of it are identified. Two algorithms based on the well-known Davis Putnam search procedurea represented so as to solve DISTANCE-SAT. Their empirical evaluation enables deriving firm conclusionsa bout their respective performances and to relate the difficulty of DISTANCE-SAT with the difficulty of SAT from the practical side.
@cite_31: Users can often naturally express their preferences in terms of ideal or non-ideal solutions. We show how to reason about logical combinations of distance constraints on ideals and non-ideals using a novel global constraint. We evaluate our approach on both randomly generated and real-world configuration problem instances.
@cite_23: It is useful in a wide range of situations to find solutions which are diverse (or similar) to each other. We therefore define a number of different classes of diversity and similarity problems. For example, what is the most diverse set of solutions of a constraint satisfaction problem with a given cardinality? We first determine the computational complexity of these problems. We then propose a number of practical solution methods, some of which use global constraints for enforcing diversity (or similarity) between solutions. Empirical evaluation on a number of problems show promising results.
Considering partial Hamming distance as in @cite_24 , present an offline method (similar to our method) that applies clustering methods, and two online methods: one based on reformulation (similar to Online Method 1), the other based on a greedy algorithm (similar to Online Method 2) that iteratively computes a solution that maximizes similarity to previous solutions. The computation of a @math -close solution is due to a Branch & Bound algorithm (similar to the idea behind Online Method 3) that propagates some similarity diversity constraints specific to the given distance function. Our offline online methods are inspired by these methods of @cite_31 @cite_23 .