weightederm 0.1.0

Scikit-learn-style weighted empirical risk minimization for changepoint detection

weightederm

weightederm is a scikit-learn-style package for change point detection in regression settings via weighted empirical risk minimization (WERM).

It currently provides fixed- and CV-based estimators for:

Loss	Fixed num_chgpts	Unknown num_chgpts via CV
Least squares	WERMLeastSquares	WERMLeastSquaresCV
Huber	WERMHuber	WERMHuberCV
Logistic (binary)	WERMLogistic	WERMLogisticCV

Installation

Using pip

pip install git+https://github.com/gabrielarpino/weightederm.git

From root after cloning

Install from the repository root with standard Python packaging tools:

pip install .

For editable local development:

pip install -e .

If you are using uv, the equivalent setup command is:

uv sync

This repository is already source-installable: building with uv build produces both an sdist and a wheel.

Quick Notes

• Observations are assumed to be ordered.
• num_signals = num_chgpts + 1.
• delta constrains the changepoint search only; it does not currently change the prior weights.
• CV defaults:
  • least squares / Huber: absolute-loss model selection
  • logistic: logistic-loss model selection
• Set use_base_loss_for_cv=True on a CV estimator to score folds with the estimator's base loss instead.
• Unpenalized logistic fits can fail on separable data. In that case weightederm raises rather than silently regularizing.

Minimum Working Examples

These examples are intentionally small, deterministic, and tested. They are not full reproductions of the benchmark notebook, but they follow the same spirit as minimal M1/M2/M3-style runs.

M1-style: fixed number of changepoints, sparse linear regression

# README_TEST_M1
import numpy as np
from weightederm import WERMLeastSquares

rng = np.random.default_rng(0)
n, p = 120, 20
true_cp = 60

X = rng.normal(size=(n, p))
beta_left = np.zeros(p)
beta_left[[0, 3]] = [2.0, -1.5]
beta_right = np.zeros(p)
beta_right[[0, 3]] = [-1.0, 2.5]

y = np.empty(n)
y[:true_cp] = X[:true_cp] @ beta_left + 0.2 * rng.normal(size=true_cp)
y[true_cp:] = X[true_cp:] @ beta_right + 0.2 * rng.normal(size=n - true_cp)

model = WERMLeastSquares(
    num_chgpts=1,
    delta=5,
    search_method="efficient",
    fit_intercept=False,
)
model.fit(X, y)

print("true changepoint:", true_cp)
print("estimated changepoint:", model.changepoints_[0])
assert abs(int(model.changepoints_[0]) - true_cp) <= 5

M2-style: unknown number of changepoints, sparse linear regression with CV

# README_TEST_M2
import numpy as np
from weightederm import WERMLeastSquaresCV

rng = np.random.default_rng(1)
n, p = 180, 10
true_cps = np.array([60, 120])

X = rng.normal(size=(n, p))
beta_1 = np.zeros(p)
beta_1[[0]] = [3.5]
beta_2 = np.zeros(p)
beta_2[[0, 1]] = [-3.0, 3.0]
beta_3 = np.zeros(p)
beta_3[[0, 1, 2]] = [2.5, -2.5, 2.5]

y = np.empty(n)
y[:60] = X[:60] @ beta_1 + 0.05 * rng.normal(size=60)
y[60:120] = X[60:120] @ beta_2 + 0.05 * rng.normal(size=60)
y[120:] = X[120:] @ beta_3 + 0.05 * rng.normal(size=60)

model = WERMLeastSquaresCV(
    max_num_chgpts=2,
    delta=5,
    cv=3,
    search_method="efficient",
    fit_intercept=False,
)
model.fit(X, y)

print("true changepoints:", true_cps.tolist())
print("selected num_chgpts:", model.best_num_chgpts_)
print("estimated changepoints:", model.changepoints_.tolist())
assert model.best_num_chgpts_ == 2
assert np.max(np.abs(model.changepoints_ - true_cps)) <= 5

M3-style: fixed number of changepoints, sparse logistic regression

# README_TEST_M3
import numpy as np
from weightederm import WERMLogistic

rng = np.random.default_rng(2)
n, p = 160, 12
true_cp = 80

X = rng.normal(size=(n, p))
beta_left = np.zeros(p)
beta_left[[0, 2]] = [2.5, -2.0]
beta_right = np.zeros(p)
beta_right[[0, 2]] = [-2.5, 2.0]

eta = np.empty(n)
eta[:true_cp] = X[:true_cp] @ beta_left
eta[true_cp:] = X[true_cp:] @ beta_right
prob = 1.0 / (1.0 + np.exp(-eta))
y = rng.binomial(1, prob)

model = WERMLogistic(
    num_chgpts=1,
    delta=5,
    search_method="efficient",
    fit_intercept=False,
    max_iter=300,
    tol=1e-6,
)
model.fit(X, y)

print("true changepoint:", true_cp)
print("estimated changepoint:", model.changepoints_[0])
assert abs(int(model.changepoints_[0]) - true_cp) <= 5

For fuller benchmark-style experiments, including normalized Hausdorff summaries and optional McScan comparison, see notebooks/reference_like_m123_benchmarks.ipynb.