I am using Katz_centrality to determine the centrality measures for nodes in the network Julia 1.1.0. However, it yields negative values. Shouldn’t centrality scores be positive ?

In order for the Katz results to be valid, the attenuation factor must be a positive number smaller than the maximum of the absolute values of the eigenvalues of the adjacency matrix. You will very likely get negative if you use a larger factor. It’s just like summing an infinite geometric series using the formula 1/(1-r): It’s only valid if abs® < 1.