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Eugene Clark
Active galaxies are characterized by large power output from the central regions. There are a multitude of observed classes of these Active Galactic Nuclei (AGN). A major goal of modern astrophysics is to explain the diversity of observed AGNs within a common physical framework that allows for evolution of individual sources with redshift (and hence cosmic time). Data from recent, large-scale sky surveys supply a wealth of information on AGNs. Principal component analyses provide a means to search for dominant correlations among many observables, which will help to improve our understanding of the physics of these objects.