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Greedy Randomized Adaptive Search Procedures For The Steiner Problem In Graphs
 QUADRATIC ASSIGNMENT AND RELATED PROBLEMS, VOLUME 16 OF DIMACS SERIES ON DISCRETE MATHEMATICS AND THEORETICAL COMPUTER SCIENCE
, 1999
"... We describe four versions of a Greedy Randomized Adaptive Search Procedure (GRASP) for finding approximate solutions of general instances of the Steiner Problem in Graphs. Di#erent construction and local search algorithms are presented. Preliminary computational results with one of the versions ..."
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Cited by 123 (31 self)
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We describe four versions of a Greedy Randomized Adaptive Search Procedure (GRASP) for finding approximate solutions of general instances of the Steiner Problem in Graphs. Di#erent construction and local search algorithms are presented. Preliminary computational results with one of the versions on a variety of test problems are reported. On the majority of instances from the ORLibrary, a set of standard test problems, the GRASP produced optimal solutions. On those that optimal solutions were not found, the GRASP found good quality approximate solutions.
The Quadratic Assignment Problem: A Survey and Recent Developments
 In Proceedings of the DIMACS Workshop on Quadratic Assignment Problems, volume 16 of DIMACS Series in Discrete Mathematics and Theoretical Computer Science
, 1994
"... . Quadratic Assignment Problems model many applications in diverse areas such as operations research, parallel and distributed computing, and combinatorial data analysis. In this paper we survey some of the most important techniques, applications, and methods regarding the quadratic assignment probl ..."
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Cited by 109 (16 self)
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. Quadratic Assignment Problems model many applications in diverse areas such as operations research, parallel and distributed computing, and combinatorial data analysis. In this paper we survey some of the most important techniques, applications, and methods regarding the quadratic assignment problem. We focus our attention on recent developments. 1. Introduction Given a set N = f1; 2; : : : ; ng and n \Theta n matrices F = (f ij ) and D = (d kl ), the quadratic assignment problem (QAP) can be stated as follows: min p2\Pi N n X i=1 n X j=1 f ij d p(i)p(j) + n X i=1 c ip(i) ; where \Pi N is the set of all permutations of N . One of the major applications of the QAP is in location theory where the matrix F = (f ij ) is the flow matrix, i.e. f ij is the flow of materials from facility i to facility j, and D = (d kl ) is the distance matrix, i.e. d kl represents the distance from location k to location l [62, 67, 137]. The cost of simultaneously assigning facility i to locat...
Choosing work group members: Balancing similarity, competence, and familiarity
 Organizational Behavior and Human Decision Processes
, 2000
"... This study explores one of the contributors to group composition—the basis on which people choose others with whom they want to work. We use a combined model to explore individual attributes, relational attributes, and previous structural ties as determinants of work partner choice. Four years of da ..."
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Cited by 60 (2 self)
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This study explores one of the contributors to group composition—the basis on which people choose others with whom they want to work. We use a combined model to explore individual attributes, relational attributes, and previous structural ties as determinants of work partner choice. Four years of data from participants in 33 small project groups were collected, some of which reflects individual participant characteristics and some of which is social network data measuring the previous relationship between two participants. Our results suggest that when selecting future group members people are biased toward others of the same race, others who have a reputation for being competent and hard working, and others with whom they have developed strong working relationships in the past. These results suggest that people strive for predictability when choosing future work group members. � 2000 Academic Press People often play either a direct or an indirect role in choosing their work partners. In volunteer organizations, people decide which group or committee to join. Academics decide who to collaborate with on research projects. And,
The network of innovators in Jena: An application of social network analysis
 Research Policy
, 2006
"... First draft Please do not cite without permission of the authors We apply social network analysis methods to describe the evolution of the innovator network of Jena, Germany in the period from 1995 to 2001. We find this evolution to be directed towards an increasing focus on core competencies of th ..."
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Cited by 52 (6 self)
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First draft Please do not cite without permission of the authors We apply social network analysis methods to describe the evolution of the innovator network of Jena, Germany in the period from 1995 to 2001. We find this evolution to be directed towards an increasing focus on core competencies of the local innovation system. Further we analyze the network resulting from R&D cooperations and explain by means of network regression techniques that the job mobility of scientists and the technological overlap between the actors, rather than past cooperations, can best predict the resulting structure. We also observe an increasing importance of the university while the former “Kombinate ” begin to lose their prominent role.
SENSITIVITY OF MRQAP TESTS TO COLLINEARITY AND AUTOCORRELATION CONDITIONS
, 2007
"... Multiple regression quadratic assignment procedures (MRQAP) tests are permutation tests for multiple linear regression model coefficients for data organized in square matrices of relatedness among n objects. Such a data structure is typical in social network studies, where variables indicate some ty ..."
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Cited by 38 (1 self)
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Multiple regression quadratic assignment procedures (MRQAP) tests are permutation tests for multiple linear regression model coefficients for data organized in square matrices of relatedness among n objects. Such a data structure is typical in social network studies, where variables indicate some type of relation between a given set of actors. We present a new permutation method (called “double semipartialing”, or DSP) that complements the family of extant approaches to MRQAP tests. We assess the statistical bias (type I error rate) and statistical power of the set of five methods, including DSP, across a variety of conditions of network autocorrelation, of spuriousness (size of confounder effect), and of skewness in the data. These conditions are explored across three assumed data distributions: normal, gamma, and negative binomial. We find that the Freedman–Lane method and the DSP method are the most robust against a wide array of these conditions. We also find that all five methods perform better if the test statistic is pivotal. Finally, we find limitations of usefulness for MRQAP tests: All tests degrade under simultaneous conditions of extreme skewness and high spuriousness for gamma and negative binomial distributions.
Computing lower bounds for the quadratic assignment problem with an interior point algorithm for linear programming
 Operations Research
, 1995
"... A typical example of the quadratic assignment problem (QAP) is the facility location problem, in which a set of n facilities are to be assigned, at minimum cost, to an equal number of locations. Between each pair of facilities, there is a given amount of flow, contributing a cost equal to the produc ..."
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Cited by 36 (4 self)
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A typical example of the quadratic assignment problem (QAP) is the facility location problem, in which a set of n facilities are to be assigned, at minimum cost, to an equal number of locations. Between each pair of facilities, there is a given amount of flow, contributing a cost equal to the product of the flow and the distance between locations to which the facilities are assigned. Proving optimality of solutions to quadratic assignment problems has been limited to instances of small dimension (n less than or equal to 20), in part because known lower bounds for the QAP are of poor quality. In this paper, we compute lower bounds for a wide range of quadratic assignment problems using a linear programmingbased lower bound studied by Drezner (1994). On the majority of quadratic assignment problems tested, the computed lower bound is the new best known lower bound. In 87 percent of the instances, we produced the best known lower bound. On several instances, including some of dimension n equal to 20, the lower bound is tight. The linear programs, which can be large even for moderate values of n, are solved with an interior point code that uses a preconditioned conjugate gradient algorithm to compute the directions taken at each iteration by the interior point algorithm. Attempts to
An individualoriented model of the emergence of despotic and egalitarian societies
 Proc. R
, 1999
"... Single behavioural di¡erences between egalitarian and despotic animal societies are often assumed to re£ect speci¢c adaptations. However, in the present paper, I will show in an individualorientated model, how many behavioural traits of egalitarian and despotic virtual societies arise as emergent c ..."
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Cited by 36 (5 self)
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Single behavioural di¡erences between egalitarian and despotic animal societies are often assumed to re£ect speci¢c adaptations. However, in the present paper, I will show in an individualorientated model, how many behavioural traits of egalitarian and despotic virtual societies arise as emergent characteristics. The arti¢cial entities live in a homogeneous world and only aggregate, and upon meeting one another may perform dominance interactions in which the e¡ects of winning and losing are selfreinforcing. The behaviour of these entities is studied in a similar way to that of real animals. It will be shown that by varying the intensity of aggression only, one may switch from egalitarian to despotic virtual societies. Di¡erences between the two types of society appear to correspond closely to those between despotic and egalitarian macaque species in the real world. In addition, arti¢cial despotic societies show a clearer spatial centrality of dominants and, counterintuitively, more rank overlap between the sexes than the egalitarian ones. Because of the correspondence with patterns in real animals, the model makes it worthwhile comparing despotic and egalitarian species for sociospatial structure and rank overlap too. Furthermore, it presents us with parsimonious hypotheses which can be tested in real animals for patterns of aggression, spatial structure and the distribution of social positive and sexual behaviour.
The Effects of R&D Team Colocation on Communication Patterns among R&D, Marketing, and Manufacturing
 Management Science
, 1998
"... Reducing the physical distance among R&D engineers and between R&D and marketing is widely believed to result in more frequent communication, and hence higher product development performance. However, the empirical evidence for the effect of colocation on communication frequency is problema ..."
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Cited by 34 (0 self)
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Reducing the physical distance among R&D engineers and between R&D and marketing is widely believed to result in more frequent communication, and hence higher product development performance. However, the empirical evidence for the effect of colocation on communication frequency is problematic for two reasons: (1) the evidence often features either little contextual realism or doubtful internal validity, and (2) the analysis does not deal with the statistical problems typical of network data. Our study avoids the first problem by using sequential network data collected from a quasiexperiment at an industrial company that regrouped its R&D teams into a new facility. We avoid the second problem by using Wasserman and Iacobucci's (1988) method for the statistical analysis of sequential network data. Our results show that communication among R&D teams was enhanced after colocating these teams. Surprisingly, communication frequency between R&D and marketing was not affected by the increa...
The rowwise correlation between two proximity matrices and the partial rowwise correlation. Psychometrika 58: 53–69
, 1993
"... This paper discusses rowwise matrix correlation, based on the weighted sum of correlations between all pairs of corresponding rows of two proximity matrices, which may both be square (symmetric or asymmetric) or rectangular. Using the correlation coefficients usually associated with Pearson, Spearm ..."
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Cited by 21 (3 self)
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This paper discusses rowwise matrix correlation, based on the weighted sum of correlations between all pairs of corresponding rows of two proximity matrices, which may both be square (symmetric or asymmetric) or rectangular. Using the correlation coefficients usually associated with Pearson, Spearman, and Kendall, three different rowwise test statistics and their normalized coefficients are discussed, and subsequently compared with their nonrowwise alternatives like Mantel's Z. It is shown that the rowwise matrix correlation coefficient between two matrices X and Y is the partial correlation between the entries of X and Y controlled for the nominal variable that has the row objects as categories. Given this fact, partial rowwise correlations (as well as multiple regression extensions in the case of Pearson's approach) can be easily developed. Key words: matrix permutation tests, rowwise matrix correlation, partial matrix correlation, Mantel's Z statistic, nonparametric statistics.
Cooperation Without Genes, Games Or Cognition.
 In
, 1997
"... In this paper I describe how the spatial dynamics of autocatalytic interactions among entities in a virtual world led to a type of cooperation that typically would be studied from a game theoretical perspective. The entities were very simple and completely identical at the start of the simulation. ..."
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Cited by 21 (8 self)
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In this paper I describe how the spatial dynamics of autocatalytic interactions among entities in a virtual world led to a type of cooperation that typically would be studied from a game theoretical perspective. The entities were very simple and completely identical at the start of the simulation. They just aggregated and performed aggressive interactions in which winning was selfreinforcing. Patterns of reciprocation emerged at the level of the group, particularly in loose assemblages. These patterns appeared not to be due to global spatial structures as I have suggested before (Hemelrijk, 1996ab), but arose from local series of Titfor Tat like interactions. These involved pairs of individuals that 'collaborated` by taking turns in chasing away a third entity. Runs with varying parameter values showed that particularly those entities that were designed to be more aggressive, were more prone to cooperate. The processes responsible for the TitforTat like patterns are outlined. It ...