atomic Devlog #3: solver, server, and the web instrument
Three phases landed since last time: the numerical solver, the FastAPI backend, and the React + Three.js frontend. 193 backend tests and 48 frontend tests green, everything pushed.
Change 1: numerical radial solver
Built a 3-point finite-difference solver for arbitrary central potentials, plus a grid-halving error estimator. Validated against the exact hydrogen answers: energies match, 1s overlap > 0.99999, convergence measures exactly 2.00 across all cases. Two of my own test assertions were wrong along the way (forgot reduced mass in the expected energy, grid too coarse for the normalization check) — the engine was right both times.
Change 2: FastAPI backend
atomic serve now runs a real server: health, systems, state, levels, radial endpoints, plus background jobs (cloud sampling, plane cross-sections) with websocket progress and binary data channels. Sampling is honest inverse-transform Monte Carlo of |psi|². Also fixed a URL-encoding bug where the he+ key decoded as “he “ and got refused everywhere — verified against the live server.
Change 3: web instrument
Full frontend: orbitable 3D point clouds with density/phase coloring, y=0 plane canvas views, clickable energy ladders, radial R/P plots with node marks and mean-radius markers, shareable URLs for every state, zustand store underneath. Production build splits Three.js into a lazy chunk; the server mounts the built UI directly.