Some 3D codes still use a spherical grid, while many others employ Cartesian AMR grids. Recent innovative approaches use so-called multi-block grids with multiple curvilinear touching or overlapping logically Cartesian “cubed-sphere” grids (e.g., [@wongwathanarat:10]).

Multi Physics
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Core-collapse supernovae are very rich in physics. All fundamental forces are involved and essential to the core collapse phenomenon. These forces are probed under conditions that are impossible (or exceedingly difficult) to create in earthbound laboratories.

Gravity drives the collapse and provides the energy reservoir. It is so strong near the protoneutron star that general relativity becomes important and its Newtonian description does not suffice. The electromagnetic force describes the interaction of the dense, hot magnetized, perfectly conducting plasma and the photons that provide thermal pressure and make the supernova light. The weak force governs the interactions of neutrinos and the strong (nuclear) force is essential in the nuclear EOS and nuclear reactions.

All this physics occurs at the microscopic, per particle level. Fortunately, the continuum assumption holds, allowing us to describe core-collapse supernovae on a macroscopic scale by a coupled set of systems of non-linear partial differential equations (PDEs):

![Map projections of the momentum-space neutrino radiation field (for $\nu_e$ at an energy 