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perf: eliminate Math.sqrt from force-directed repulsion hot path - #148
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Replace sqrt + division with squared-distance arithmetic in both QuadTree Barnes-Hut traversal and brute-force repulsion: - force = k²/dist; f_x = dx/dist * force → f_x = dx * k²/distSq - Barnes-Hut check: size/dist < theta → size² < theta² * distSq This avoids ~V*log(V) sqrt calls per iteration for Barnes-Hut mode and ~V²/2 calls for brute-force mode. The force direction is preserved since dx/distSq gives the correct unit vector scaling. Pre-compute k² and theta² outside the per-vertex loop to avoid redundant multiplication.
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Eliminates redundant Math.sqrt() calls from force-directed layout repulsion (both Barnes-Hut and brute-force paths). Replaces sqrt+division with squared-distance arithmetic: force = k²/dist becomes fx = dx * k²/distSq. Barnes-Hut check uses size² < theta² * distSq. Pre-computes k² and theta² outside the per-vertex loop. For 1000 nodes / 300 iterations, saves ~3M sqrt calls in Barnes-Hut mode.