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Internals — what lives where

A guided tour of the source tree for new contributors. If you only need to use QQA4CO see Quickstart; if you want to add a new problem, relaxation, or backend see Extending QQA4CO. This page is for everyone who wants to read the code.

Top-level layout

QQA4CO/
├── src/qqa/             # The Python package (everything ships in the wheel)
├── app/                 # Streamlit dashboard (also shipped in the wheel)
├── tests/               # 11 pytest files, < 60 s on CPU
├── notebooks/           # Curated walkthroughs (CRA-PI-GNN, CPRA)
├── examples/            # Auto-generated per-problem notebooks
├── scripts/             # Demos, benchmarks, gallery / verification regen
├── docs/                # MkDocs-Material source (this site)
├── data/                # Bundled MIS-ER datasets, gallery assets
├── deploy/              # Streamlit Cloud config
├── tasks/               # Maintainer-only journal: todo.md + lessons.md
├── pyproject.toml       # PEP 621, hatchling, ruff, pytest, extras
├── mkdocs.yml           # Site nav (this site is built from docs/)
├── CHANGELOG.md         # Keep-a-Changelog
├── CITATION.cff         # GitHub citation widget + Zenodo
├── CONTRIBUTING.md      # Setup, tests, style, PR process
├── CODE_OF_CONDUCT.md   # Contributor Covenant
├── SECURITY.md          # Vulnerability reporting
├── Makefile             # `make test / lint / format / docs / serve`
└── README.md            # The 30-second pitch and the long sales page

tasks/ is a maintainer journal that we keep in git so future-us can re-derive design decisions; it is not part of the public surface.

src/qqa/ — module map

src/qqa/
├── __init__.py          # Public API surface, __version__ via importlib.metadata
├── annealing.py         # The single anneal() loop and AnnealResult
├── relaxation.py        # Binary / Spin / Categorical / Instance relaxations + Protocol
├── schedule.py          # LinearBGSchedule (callable contract)
├── callbacks.py         # Callback ABC, CallbackState, History/AutoDiv/Population/Trajectory
├── utils.py             # fix_seed, generate_graph, MIS / MaxCut analytics
├── datasets.py          # Bundled MIS-ER loaders + benchmark constants
├── visualization.py     # Plot helpers (matplotlib + optional plotly)
├── cli.py               # The qqa command (argparse, no third-party deps)
├── legacy.py            # Deprecated 0.2.x batch_annealing_* shims
├── problems/
│   ├── __init__.py
│   ├── base.py          # COProblem / QUBOProblem ABCs + normalize_graph
│   ├── qubo.py          # MIS / MaxClique / MaxCut (+ batched instance variants)
│   ├── categorical.py   # Coloring, BalancedGraphPartition
│   ├── spin.py          # SpinProblem, Ising1D, EA, SK, Perceptron, Hopfield
│   ├── extras.py        # Knapsack, NumberPartitioning, VertexCover, GraphBisection,
│   │                    # MaxSAT3, TSP, QAP, NQueens
│   └── user.py          # UserProblem + load_problem_from_file (--problem-file CLI hook)
└── pignn/               # Optional CRA-PI-GNN / CPRA backends (PyG)
    ├── __init__.py      # Re-exports train_cra_pi_gnn / train_cpra_pi_gnn
    ├── _import.py       # require_pyg() with an actionable ImportError
    ├── graph.py         # extract_nx_graph + nx_to_edge_index helpers
    ├── model.py         # GCNNet (2-layer GCNConv, multi-head for CPRA)
    └── trainer.py       # The two trainer functions (returning AnnealResult)

Hard rules for changes inside src/qqa/

  1. Never import torch_geometric from qqa.__init__ or any module that does not live under qqa/pignn/. It pulls in heavy transitive deps that core users do not need; a stray import here is enough to break pip install qqa for everyone without qqa[pignn].
  2. Public API additions go in src/qqa/__init__.py and its __all__ so they show up in dir(qqa) and the auto-generated API reference.
  3. Bug fixes that touch anneal() need a regression test. That loop is the central nervous system of the package; every previous bug there shipped because the diff "looked obvious".
  4. Public function signatures are append-only. Add a new keyword with a sensible default — never reorder, rename, or remove an existing argument without a deprecation cycle.

app/ — Streamlit dashboard

app/
├── streamlit_app.py     # Landing page (cache config + intro)
├── _common.py           # Cached resources shared across pages
├── _solution_viz.py     # Per-problem solution renderers
└── pages/
    ├── 1_Solve.py       # Build a problem + run anneal + show progress
    ├── 2_Visualize.py   # Re-render an AnnealResult pickle
    └── 3_Compare.py     # Hyperparameter sweeps

The wheel ships this directory under qqa/_app/ (see pyproject.toml [tool.hatch.build.targets.wheel.force-include]) so qqa gui works after pip install qqa without a repo checkout.

tests/ — what each file covers

File Covers
test_smoke.py End-to-end anneal() on each variable kind
test_qqa_correctness.py Numerical guarantees against ground truth on small instances
test_problems.py Constructor / shape contracts of binary/categorical problems
test_extra_problems.py The extras.py catalogue
test_spin_problems.py Spin-glass problems (Ising/EA/SK/Hopfield/Perceptron)
test_pignn.py Optional PyG backends — CRA-PI-GNN + CPRA
test_cli.py qqa solve / bench / version subcommands
test_gui_smoke.py Streamlit imports without a browser
test_gui_apptest.py streamlit.testing harness on the multi-page app
test_visualization.py Plot helpers do not crash with a minimal AnnealResult
test_legacy.py Deprecated batch_annealing_* aliases still emit a DeprecationWarning

The full suite finishes in well under a minute on CPU because every problem instance is intentionally tiny.

scripts/ — runnable demos and reproducibility

Listed in docs/reference/backends.md and partially on the README. The categories:

  • demo_*.py — single-problem walkthroughs you can run as uv run python scripts/demo_mis.py.
  • bench_*.py — small benchmarks; bench_qqa_vs_pignn.py regenerates the headline comparison table.
  • make_gallery.py — regenerates the README/docs gallery PNGs.
  • verify_all_problems.py — the catalogue-wide correctness sweep that produces docs/verification.md.
  • _generate_notebooks.py — deterministically rebuilds the examples/ notebooks (the leading underscore signals "internal tooling").
  • check_streamlit_deploy.py — health probe for the hosted demo at https://parallelquasiquantum4co.streamlit.app/.

How tests, docs, and CI relate

.github/workflows/ci.yml
        │
        ├── ruff check + ruff format --check
        ├── pytest -q                  ← uses tests/
        └── mkdocs build --strict      ← uses docs/ and mkdocs.yml

A PR that breaks any of those three steps is automatically blocked. There is also a Pages workflow that publishes the same mkdocs build output to https://yuma-ichikawa.github.io/QQA4CO/ on every push to main.

Where to start a typical PR

  1. Open tasks/todo.md, scroll to the bottom, and skim the most recent dated section — that is where active work is journaled.
  2. Run the whole test suite once locally before you start; that becomes your baseline.
  3. After every change run make lint test docs (or the equivalent uv run ... commands listed in CONTRIBUTING.md).
  4. If your change adds a public-API symbol, also add it to docs/api.md so mkdocstrings picks it up.
  5. Add an entry to CHANGELOG.md under the Unreleased heading.

That is the whole loop. See Releasing for what happens once changes accumulate to a tag.