***** To join INSNA, visit http://www.insna.org ***** You are wrong. Eigenvector centrality finds the dominant eigenvector of the matrix you prescribe as data. If this has values it takes them and uses them. On 6 Apr 2005 at 21:29, Scott White wrote: > Also I believe eigenvector centrality is computed on the adjacency > matrix and not on the transition matrix so that edges are *not* in > fact weighted. Someone correct me if I'm wrong. > > Scott > > On Tue, 29 Mar 2005 11:54:18 +0100, "[log in to unmask]" > <[log in to unmask]> said: > > ***** To join INSNA, visit http://www.insna.org ***** > > > > I feel I must correct what Joshua has said. > > > > 1 Both UCINET and MATLAB produce the correct results. They do not > > test for singularity (as this merely says that zero is an > > eigenvalue) but use sophisticated (particularly MATLAB) specialist > > routines. > > > > 2 The method Joshua describes is the power method and is a well > > known technique for finding eigenvectors in special cases. One of > > those cases is if the graph is connected. If the graph is not > > connected the method may fail, that is it will not find an > > eigenvector. Usually it simply does not converge and hence you may > > get some values but these cannot be interpreted as eigenvectors, > > they are not. > > > > 3 One possible way to use eigenvector centrality on disconnected > > graphs is to take the eigenvectors corresponding to the smaller > > eigen values. UCINET reports the dominant eigenvector ie the > > eigenvector corresponding to the largest eigenvalue. This will have > > positive values for the largest component and zero for all other > > components. The other eigenvalues will have eigenvectors that have a > > zero for all elements of the largest component but have non zero > > values for one of the others. You could compare the centralities > > within each component, I guess but care would be needed in > > interpretation. To do this in UCINET you need to run the svd command > > in the matrix algebra section. It is easy to do using the eigenvalue > > command in MATLAB. > > > > Personally I would not recommend eigenvector centrality for graphs > > with multiple components. > > > > > > > > > > On 29 Mar 2005 at 2:14, Joshua O'Madadhain wrote: > > > > > ***** To join INSNA, visit http://www.insna.org ***** > > > > > > Skye: > > > > > > I believe that what's going on here is that eigenvector centrality > > > is defined in a way that the closed-form calculation of it > > > requires calculation of the inverse of the network's (weighted) > > > matrix. I would guess that UCINET and matlab are both calculating > > > EVC in this way. Since I'm pretty sure that the matrix of such a > > > network is singular (i.e., it has no inverse), I'd hazard a guess > > > that the implementors of EVC on these platforms simply tested for > > > this condition and ran the calculation on the largest component. > > > > > > However, you can calculate eigenvector centrality by iterative > > > approximation: essentially, you start every node out with an equal > > > amount of "potential", and that potential is allowed to flow along > > > edges in proportion to their edge weights; continue until the > > > potential stops changing. This is the method that JUNG uses, and > > > I've just confirmed that it appears to work fine--that is, assigns > > > non-zero values that seem plausible--on a network with > > > disconnected components. > > > > > > If you want to try this with JUNG, you'll want the PageRank class > > > with bias set to 0; let me know if you have any questions. > > > > > > Hope this helps-- > > > > > > Joshua O'Madadhain > > > > > > On 8 Mar 2005, at 8:28, Skye Bender-Demoll wrote: > > > > > > > ***** To join INSNA, visit http://www.insna.org ***** > > > > > > > > Hi all, > > > > > > > > Does anybody have any experience with / references for > > > > eigenvalue centrality measures and graphs with multiple > > > > components? > > > > > > > > We are starting to work with the standard eigenvector > > > > centrality > > > > measure, > > > > but the networks we use contain multiple components. Not > > > > surprisingly, this seems to cause some problems. The > > > > eigenvector calculation (both in UCINET and in matlab) gives > > > > correct results for the largest components, but zero for all the > > > > other components. When we run the calculation on one component > > > > alone, we get very different results. I'm guessing that the > > > > eigenvector centrality measure is not defined for multiple > > > > components? (UCINET seems to suggest this) > > > > > > > > Or are the values for the smaller component (a three node chain > > > > in a test example) so small when compared with the large > > > > component (a 5 node bow-tie) that they are lost in round off > > > > during the eigenvector calculation? > > > > > > > > If we run the algorithm independently on each component, can we > > > > compare scores between components, or are they only valid within > > > > components? (I'm assuming that in the UCINET-style version where > > > > the scores are normalized they should only be compared within > > > > components?) > > > > > > > > Any suggestions welcome ( I have yet to locate many papers > > > > directly related to this, nor in the socnet archives) > > > > > > > > 1) R. Poulin, M.-C. Boily B.R. Masse (2000) "Dynamical systems > > > > to define centrality in social networks" Social Networks 22 > > > > 187–220 > > > > > > > > thanks, > > > > -skye > > > > ATA S.p.A Lucca Italy > > > > > > > > ________________________________________________________________ > > > > ____ _ SOCNET is a service of INSNA, the professional > > > > association for social network researchers > > > > (http://www.insna.org). To unsubscribe, send an email message to > > > > [log in to unmask] containing the line UNSUBSCRIBE SOCNET in > > > > the body of the message. > > > > > > > jmadden@ics.uci.edu...Obscurium Per > > > Obscurius...www.ics.uci.edu/~jmadden Joshua O'Madadhain: > > > Information Scientist, Musician, and Philosopher-At-Tall > > > It's that moment of dawning comprehension that I live for--Bill > > > Watterson > > > My opinions are too rational and insightful to be those of any > > > organization. > > > > > > __________________________________________________________________ > > > ___ SOCNET is a service of INSNA, the professional association for > > > social network researchers (http://www.insna.org). To unsubscribe, > > > send an email message to [log in to unmask] containing the > > > line UNSUBSCRIBE SOCNET in the body of the message. > > > > > > > > Martin Everett > > Marylebone Provost > > University of Westminster > > 35 Marylebone Road > > London NW1 5LS > > > > Email [log in to unmask] > > Tel +44(0)20 7911 5000 Ext 3183 > > Fax +44(0)20 7911 5051 > > > > This e-mail and its attachments are intended for the above named > > only and may be confidential. If they have come to you in error you > > must not copy or show them to anyone, nor should you take any action > > based on them, other than to notify the error by replying to the > > sender. > > > > ____________________________________________________________________ > > _ SOCNET is a service of INSNA, the professional association for > > social network researchers (http://www.insna.org). To unsubscribe, > > send an email message to [log in to unmask] containing the line > > UNSUBSCRIBE SOCNET in the body of the message. Martin Everett Marylebone Provost University of Westminster 35 Marylebone Road London NW1 5LS Email [log in to unmask] Tel +44(0)20 7911 5000 Ext 3183 Fax +44(0)20 7911 5051 This e-mail and its attachments are intended for the above named only and may be confidential. If they have come to you in error you must not copy or show them to anyone, nor should you take any action based on them, other than to notify the error by replying to the sender. _____________________________________________________________________ SOCNET is a service of INSNA, the professional association for social network researchers (http://www.insna.org). To unsubscribe, send an email message to [log in to unmask] containing the line UNSUBSCRIBE SOCNET in the body of the message.