Your search for: 'author:("Levene, Mark")' has returned 5 results. (0.008s) Save search

Authors: Fenner, Trevor | Levene, Mark

Article Type: Research Article

Abstract: We present two new perfect hashing schemes that can be used for efficient bitboard move generation for sliding pieces in chess-like board games without the need to use rotated bitboards. Moreover, we show that simple variations of these schemes give minimal perfect hashing schemes. The new method is applicable provided N , the number of k -bit spaced positions that may be set to 1, is not more than k + 1. In chess, for a Rook’s movement along a file N = k = 8; for a Bishop’s movement N ≤ 8, and k = 9 for a north-east …diagonal and k = 7 for a north-west diagonal. The results of computational experiments comparing the efficiency of move generation with the standard method show that using the hashing scheme gives an average improvement of approximately 40%. The schemes we suggest are simple, efficient, and easy to understand and implement. Show more

DOI: 10.3233/ICG-2008-31102

Citation: ICGA Journal, vol. 31, no. 1, pp. 3-12, 2008

Authors: Levene, Mark | Fenner, Trevor

Article Type: Research Article

Abstract: Random minimaxing, introduced by Beal and Smith, is the process of using a random static evaluation function for scoring the leaf nodes of a full-width game tree and then computing the best move using the standard minimax procedure. Their experiments using random minimaxing in chess showed that the strength of play increases with the depth of the lookahead. We investigate random minim axing combinatorially in order to obtain a theoretical justification for Beal and Smith’s experiments. In particular, we show that, with respect to chess, random minim axing with the depth of lookahead equal to two is ‘stronger’ than the …same with its depth equal to unity, under the assumption that a move by the first player is better the more it restricts the second player’s choice of moves (i.e., his mobility). We conjecture that these results can be generalized for depths of lookahead greater than two. Show more

DOI: 10.3233/ICG-1995-18103

Citation: ICGA Journal, vol. 18, no. 1, pp. 20-33, 1995

Authors: Levene, Mark | Loizou, George

Article Type: Research Article

Abstract: The nested relational model extends the fiat relational model by relaxing the first normal form assumption in order to allow the modelling of complex objects. Recently many extended algebras have been suggested for the nested relational model, but only few have incorporated null values into the attribute domains. Furthermore, some of the previously defined extended algebras are defined only over a subclass of nested relations, and all of them are difficult to use, since the user must know the detailed structure of the nested relations being queried. Herein, we define an extended algebra for nested relations, which may contain null …values, called the null extended algebra . The null extended algebra is defined over the general class of nested relations with null values and, in addition, allows queries to be formulated without the user having to know the detailed structure of the nested relations being queried. In this sense, our null extended join operator of the null extended algebra is unique in the literature, since it joins two nested relations by taking into account all their common attributes at all levels of their structure, whilst operating directly on the two nested relations. All the operators of the null extended algebra are proved to be faithful and precise . The null extended algebra is a complete extended algebra in the context of nested relations, and, in addition, it includes the null extended powerset operator , which provides recursion and iteration facilities. Show more

Keywords: nested relations, null values, null extended algebra, faithful extended algebra operators, precise extended algebra operators

DOI: 10.3233/FI-1993-193-405

Citation: Fundamenta Informaticae, vol. 19, no. 3-4, pp. 303-342, 1993

Authors: Levene, Mark | Loizou, George

Article Type: Research Article

Abstract: We present an alternative approach to that of Chandra and Harel [5] and Abiteboul and Vianu [1] in considering computable database queries, which are mappings from sets of records to sets of records. In particular, we view a computable database query as being realised via a Turing-computable mapping from strings to strings and an encoding, which encodes the input set of records into an appropriate string. An encoding of a set of records consists of two components: an ordering function, which orders the records in a set as well as the values of each record in the set, and an …isomorphism, which maps the values in the records of the set to strings. An important class of encodings, called free encodings, whose isomorphism has the same semantics as the identity mapping on record values, is also defined. Our analysis of computable database queries elucidates the notion of a computable database query by dealing with the problem of how a database language can be implemented on a standard Turing machine that does not cater directly for mappings from sets of records to sets of records. We carry out our analysis by categorising computable database queries into subclasses and by establishing the relationships that exist amongst these subclasses. We also investigate an equivalence relation on computable database queries; two computable database queries are related if they are realised via the same Turing-computable mapping, say δ. We prove the following interesting result regarding the cardinality of the equivalence class of a computable query with respect to the said equivalence relation: either δ does not realise any computable query, or δ realises exactly one computable query, or δ realises a countably infinite set of computable queries. Our final result shows that, by adding membership queries to the class of encoding-independent computable queries, the closure of the resulting extended class under composition of mappings is the set of all isomorphism-independent computable queries. Show more

DOI: 10.3233/FI-1996-27401

Citation: Fundamenta Informaticae, vol. 27, no. 4, pp. 319-348, 1996

Authors: Levene, Mark | Bar-Ilan, Judit

Article Type: Research Article

Abstract: Anecdotal evidence exists that in many positions two distinct chess engines will choose different moves and, moreover, that their top-n ranking of move choices also differ. Here we set out to quantify this difference, including the difference between move choices by chess engines and those made by humans. For our analysis we used FRITZ 8 and JUNIOR 9 as representative chess search engines and the POWERBOOK opening book as representing human choices. We collected the top-5 ranked moves and their scores as reported by FRITZ and JUNIOR , after 15 and 30 minutes of thinking time, and the top-5 moves …recorded in the POWERBOOK , for the Nunn2 test positions and the initial board position. The data analysis was carried out using several nonparametric measures, including the amount of overlap in the top-5 choices of the engines and their association as measured by three variants of Spearman’s footrule. Our preliminary results show that, overall, the engines differ substantially in their choice of moves, and, furthermore, the engines’ choices also differ substantially from human choice. Show more

DOI: 10.3233/ICG-2005-28202

Citation: ICGA Journal, vol. 28, no. 2, pp. 67-76, 2005