# stan-remote-sampling

Compile and sample Stan models from the browser, with all computation remote:

- **Compile**: the Stan program is sent to
  [stan-wasm-wasi](https://stan-wasm-wasi.fly.dev) (a
  [stan-playground](https://github.com/flatironinstitute/stan-playground)
  compilation server variant), which returns the model compiled as a **pure
  WASI command module** — a sandboxed `.wasm` that runs one MCMC chain per
  invocation.
- **Sample**: each chain is submitted as one job to a
  [wasm-exec](https://github.com/magland/wasm-exec) service (default
  `https://wasm-exec.fly.dev`), which relays it to attached workers. Progress
  streams back live (SSE stderr events → per-chain progress bars); draws
  come back as CSV (SSE stdout events) and are merged across chains.

Live app: https://concept-collection.github.io/stan-remote-sampling/

You need a wasm-exec **client key** (`ck_...`) to sample; it is stored in
localStorage.

## Notes

- Chains share a seed and get distinct chain ids (CmdStan convention), so a
  multi-chain run is statistically equivalent to CmdStan's.
- First compile after server idle pays a ~30 s machine cold start; compiled
  models are cached by program hash, so recompiles are instant.
- wasm-exec jobs run with no filesystem and no network, a 256 MiB memory cap,
  and a wall-clock timeout. Draw output is bounded by wasm-exec's 10 MiB
  per-stream cap.

## Development

```bash
npm install
npm run dev     # http://localhost:3000
```

Deployment to GitHub Pages is automatic on push to `main`
(`.github/workflows/deploy.yml`).

## History

Built in stages: (1) in-browser sampling with one web worker per chain via
tinystan (since removed — see git history), (2) a prototype proving Stan
models compile to pure-WASI modules (now the
[stan-wasm-wasi](https://github.com/magland/stan-wasm-wasi) repo), (3) this
remote-only app.