Mathematical model - Python and JS Sources for Ankle Brachial Index

This release provides the pure mathematical model and reference implementation for ABI (Ankle–Brachial Index) calculation, delivered as source code in both JavaScript and Python. The implementation defines the ABI computation as a deterministic function of bilateral arm systolic pressures and bilateral ankle systolic pressures, using the higher brachial pressure as the reference denominator. The model explicitly treats any non-positive input (≤ 0) as an invalid/missing-data sentinel for mathematical purposes, not as a physiological or clinical condition. When division is undefined (reference arm ≤ 0), the function returns null ABI values. When ankle inputs are invalid, the function returns a defined sentinel output to preserve deterministic behavior and simplify downstream UI handling. ABI outputs are rounded to two decimal places for consistent presentation. This package is intended as a transparent, implementation-oriented specification for reproducible ABI computation across platforms. It does not provide clinical guidance, does not replace clinician judgment, and does not imply medical device certification.