hallmodel 2026.6.19.6

Python interface to the Hall body-weight dynamics models, backed by the hallmodel-core C++ kernel.

hallmodel-py

Python interface to the Hall adult- and child- body-weight dynamics models, backed by the C++ kernel in hallmodel-core (vendored here as a git submodule).

The kernel is the same math the R package INSP-RH/bw compiles. Compiled in matched toolchains with -ffp-contract=off, the outputs are byte-for-byte reproducible against the upstream parity contract; under the contract's published tolerance (rtol=1e-9, atol=1e-12), all 18 contract cases pass.

This is the first reference consumer of hallmodel-core — it is also the worked example for "here is how you write a new language binding against the core."

---

Install

git clone --recurse-submodules <repo-url> hallmodel-py
cd hallmodel-py
python3 -m venv .venv && source .venv/bin/activate
pip install -e .

Build needs a C++17 compiler and pybind11 (declared in pyproject.toml).

If you cloned without --recurse-submodules:

git submodule update --init --recursive

Use

import bw_cpp

# Adult model — single individual, baseline EI from Mifflin-St Jeor
res = bw_cpp.adult_weight(bw=76, ht=1.73, age=36, sex="male")
print(res["Body_Weight"].shape)       # (1, 366)

# Adult with a 500-kcal deficit over 365 days
import numpy as np
res = bw_cpp.adult_weight(
    bw=90, ht=1.80, age=40, sex="male",
    EIchange=np.full((1, 365), -500.0),
)

# Child model — auto FFM/FM/EI defaults from age + sex
res = bw_cpp.child_weight(age=6, sex="male", days=365)

# Energy interpolation
out = bw_cpp.EnergyBuilder().build(
    energy=np.array([[2000, 2200, 1800]]),
    time=np.array([0, 5, 10]),
    method="Linear",
)

See the docstrings in bw_cpp/__init__.py for the full API, and the upstream R wrappers for the semantics of each parameter — they are the same.

Parity proof

./proof/verify.sh builds the binding against the pinned hallmodel-core submodule, drives all 18 contract cases through bw_cpp, and asserts the contract's tolerance via contract/compare.py. Exit 0 = parity holds.

./proof/verify.sh

The committed proof/last_run.log and proof/outputs/ are the frozen evidence of the most recent green run. CI re-runs them on every PR. The pinned submodule sha is the version contract: bumping it triggers a re-verify.

The one excluded field is BMI_Category — the contract's generate.R coerces character matrices through as.numeric(), producing a column of literal "NA" strings in every adult golden. See hallmodel-core/proof/verify.sh for the full explanation.

How this maps to upstream

upstream R	here
INSP-RH/bw::adult_weight()	bw_cpp.adult_weight()
INSP-RH/bw::child_weight()	bw_cpp.child_weight()
INSP-RH/bw::child_reference_EI()	bw_cpp.child_reference_EI()
INSP-RH/bw::child_reference_FFMandFM()	bw_cpp.child_reference_FFMandFM()
INSP-RH/bw::EnergyBuilder()	bw_cpp.EnergyBuilder().build()

Argument names, semantics, and defaults all match INSP-RH/bw's R wrappers because this Python shim was deliberately written as a direct port of those wrappers. The contract gate enforces it.

License

MIT, carried forward from INSP-RH/bw.

Citing

Cite the original bw package and Hall et al.'s underlying papers. See the README of INSP-RH/bw and hallmodel-core/docs/ATTRIBUTION.md.