Does a statute requiring registration of sex offenders violate a ban on ex post facto legislation?

6 Compare State v. Noble (1992) 171 Ariz. 171, 829 P.2d 1217, 1224, cited with approval in People v. McVickers (1992) 4 Cal.4th 81, 87, 13 Cal.Rptr.2d 850, 840 P.2d 955 (Arizona statute requiring registration of sex offenders did not violate the ban on ex post facto legislation because its overriding purpose was " 'facilitating the location of child sex offenders by law enforcement personnel,' a purpose unrelated to punishment").