When building a cosmological zoom-in simulation, the strategy is to run a low resolution, dark matter only simulation, select halos of interest, trace the particles that form that halo back to the initial conditions, and then build a new set of ICs with the regions that form the halo given higher resolution. In order to minimize the number of high-resolution elements needed in the zoom-in IC, the volume that is refined should hug the particles of interest as tightly as possible. Unfortunately, because the cosmic web is composed of sheets and filaments, the regions in an IC that need refinement can have complex shapes (they often look like prawn crackers). This means that simple shapes that enclose the region (cubes, ellipsoids and convex hulls are often used) will frequently contain many times the volume just traced by the particles, giving much larger (and computationally expensive). THERE HAS TO BE ANOTHER WAY!
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