Re: [igraph] eigen and evcent functions

[Tamás Nepusz]

but another question is why eigen does eigen return negative velue and  evcent positive in some cases?

Because both results are valid eigenvectors. If X is an eigenvector of a matrix, then so is -X, or c*X for any nonzero constant c. evcent() tries to make the eigenvector components positive since it is more common to treat the eigenvector centralities as positive values, but eigen() does not do that.

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T.