J. An constructed analytic hypervirial models of stellar systems with N. W. Evans. Their 2005 family combines explicit gravitational potentials, cusped density profiles and simple phase-space distribution functions, with the special property that a local virial relation holds at every radius.[ref]
Hypervirial Models of Stellar Systems by N. W. Evans and J. An. Abstract and section 2: potential-density family and moments
Such models provide controlled examples for relating density cusps and velocity anisotropy. The phase-space distribution function must remain integrable and nonnegative; an attractive density formula alone does not guarantee a physical stellar system.
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