Infrastructure and Tools

Area	Tool or technology	Purpose	Why we chose it	Version or link
Simulation Engine & Math Logic (Backend)	Python	Core backend language for simulation logic, optimization algorithms, and statistical analysis	Industry standard for mathematical modeling, discrete-event simulation, and transit operations research.	python.org (v3.12+)
	Python heapq (standard library)	Event queue and simulation clock for the discrete-event engine	A small queue owned by the team gives a fixed, documented tie order and byte-identical replays, which are the core of US-1.1. SimPy was considered; its process-based model would need extra wrapping to control tie order and the event record format.	docs.python.org/3/library/heapq (Python 3.12+)
	NumPy & SciPy	Scientific computation, probability distributions, and parameter fitting	Essential for sampling right-skewed walking and dwell times (Lognormal/Gamma), Maximum Likelihood Estimation, and isolating random substreams for Common Random Numbers (CRN) variance reduction.	scipy.org / numpy.org
	Pandas	Tabular data manipulation, time bucketing, and metric aggregation	Efficiently groups passenger records into time buckets, computes median/95th percentiles, and handles helped-versus-harmed group classifications.	pandas.pydata.org (v2.2+)
Backend API & Data Validation	FastAPI	Backend REST API server	High-performance asynchronous framework in Python; handles scenario configuration, run execution triggers, and simulation result streaming with minimal latency.	fastapi.tiangolo.com (v0.115+)
	Pydantic	Data validation, parameter clamping, and schema definition	Automatically validates simulation input parameters (e.g., maximum hold caps, headway ranges) and returns structured errors before simulation execution.	docs.pydantic.dev (v2.9+)
Frontend Framework & State	React (with TypeScript)	Frontend web application framework	Component-driven architecture with compile-time type safety; prevents state mismatches across complex passenger records, station models, and playback data.	react.dev (v18+)
	Zustand	Frontend state management for simulation playback and controls	Provides lightweight, boilerplate-free state management to synchronize the shared simulation clock, scrubbing, rewinding, and variable playback speeds (0.5x, 2x, 10x) across side-by-side views.	zustand-demo.pmnd.rs (v4.5+)
Visualization & Reporting	PixiJS	Hardware-accelerated 2D WebGL rendering engine	Renders and animates thousands of individual passenger sprites and train positions smoothly across station transfer corridors without browser DOM slowdowns.	pixijs.com (v8+)
	D3.js	Data-driven visualization library	Offers custom SVG/Canvas rendering for dual-series comparison charts, confidence intervals, percentile markers (median and 95th), and sensitivity curves.	d3js.org (v7+)
	PapaParse	Client-side CSV generation and parsing	Converts simulation output datasets into formatted CSV downloads in the browser for user data exports without adding server load.	papaparse.com (v5.4+)
	html2canvas	Client-side visual chart export	Captures rendered comparison charts and distribution graphs into high-resolution image downloads directly from the user interface.	html2canvas.hertzen.com (v1.4+)
Database & Persistence	PostgreSQL	Primary relational database	Provides reliable ACID storage for user-saved scenarios, parameter presets (peak/off-peak), and historical run manifests (seeds, code version, active operating rules).	postgresql.org (v16+)
	SQLAlchemy	Object-Relational Mapper (ORM)	Integrates PostgreSQL with FastAPI models cleanly, allowing typed queries and straightforward schema migrations.	sqlalchemy.org (v2.0+)
Testing & Verification	Pytest & Hypothesis	Backend unit and property-based testing framework	Hypothesis enables automated generation of edge-case scenarios to guarantee that safety limits (e.g., minimum headway gap, maximum hold length) are never breached.	pytest.org / hypothesis.readthedocs.io
	Ruff	Python linting and formatting	One fast tool replaces flake8, isort and black, and enforces the rubric limits on complexity (15) and statements per function (50) in CI.	docs.astral.sh/ruff (v0.17.1)
	Playwright	End-to-end (E2E) and blackbox UI testing	Automates browser workflows to verify playback controls, parameter inputs, scenario comparisons, and error state handling.	playwright.dev (v1.47+)
DevOps & CI/CD	Docker & Docker Compose	Containerization and local environment orchestration	Packages the backend engine, API, database, and frontend to guarantee consistent runtime environments and cross-platform seed determinism.	docker.com (v27+)
	GitHub Actions	Continuous Integration and Continuous Deployment (CI/CD)	Automatically executes the test suite and runs determinism verification on every push, ensuring identical seeds produce identical output hashes.	github.com/features/actions