  We introduce TRENTO, a new parametric initial condition model for high-energy
nuclear collisions based on eikonal entropy deposition via a "reduced
thickness" function. The model simultaneously describes experimental
proton-proton, proton-nucleus, and nucleus-nucleus multiplicity distributions,
and generates nucleus-nucleus eccentricity harmonics consistent with
experimental flow constraints. In addition, the model is compatible with
ultra-central uranium-uranium data unlike existing models that include binary
collision terms.
