LIVE TREE / LIVE GRAVITY
Binary disc encounter
BODIES—resident, mutually coupled
TREE NODES—— depth
FORCE TERMS—— vs direct
PROBE RMS ERROR—12 direct-force probes
What changed?
This lab is a separate self-gravitating execution path. Every resident body contributes mass to a deterministic quadtree. Distant cells may be replaced by their centre of mass when s / d < θ; nearby cells are opened. A kick–drift–kick leapfrog step rebuilds the tree after the drift.
The GALAXY rotation-law instrument remains available separately. Its huge logical populations are sampled independent test particles; they are not silently reinterpreted as mutually interacting bodies. This lab keeps the resident population explicit because self-gravity creates cross-particle coupling.