dense-armor 1.1.33

Robot-AI Online Shielding & Learning

A library for online learning on robot, vision, and AI streams, one sample at a time, with streaming statistics and protection, drift and anomaly detection, and safe robot commands.

📖 Full documentation, API reference, quick guide →

Who is this for

Python developers working on systems where data arrives one sample at a time and the model has to learn or stay stable while it runs: robot control loops, sensor pipelines, agent runtimes, any streaming workload. A fixed dataset works too: fit feeds every row to any algorithm, and the Offline learning page lists the batch versions.

Use cases

The primitives are domain-agnostic: anything that ingests data one sample at a time and has to react when the stream changes. It has been measured on a robot arm (CASPER on a UR3e), on stock and crypto prices, card transactions, network flows and a telemarketing log (the finance pages), and on synthetic streams with known drift; the layers above and below the model are the same shape everywhere.

What it expects from you

No specific model. Any estimator that follows the same contract: learn_one(x, y) updates the model from one sample, predict_one(x) returns a prediction, transform_one(x) returns a transform or a residual, score_one(x) returns an anomaly score (high = anomalous), update(x) advances a drift detector. Inputs and outputs are dicts of numpy-compatible scalars or arrays. Runs on CPU or GPU through JAX. A shield can wrap any callable from tensor to tensor.

What changes when you use it

• The model keeps learning even when the stream has NaN, spikes, or missing samples — they are cleaned before the model sees them, and every correction reports how far it moved.
• Concept drift is caught by an explicit detector instead of silently degrading accuracy.
• Anomalies come back as a score, one sample at a time.
• Robot commands are bounded (rate limits, control barrier functions) before they reach the actuator.
• Predictions can carry a calibrated uncertainty interval.

In this library, shielding means cleaning the data a model sees (NaN, spikes, anomalous samples) and bounding the commands a robot receives, around any online learner that follows the learn_one / score_one contract. It is not the formal shield of safe reinforcement learning.

What it does

Dense-Armor is a Python library for online learning. Every estimator learns one sample at a time, at control-loop speed, on JAX, and fit feeds a whole dataset to any of them. The same learn_one / predict_one / transform_one contract runs on a table, a time series, a robot joint stream, a video frame, a token stream, and a shield can sit in front of any of them.

Quickstart

As a quick example, we'll train an online Gaussian naive Bayes classifier to classify a drift stream with 5 features and one sudden concept change. Here's a look at the first observation in the dataset.

>>> from dense_armor.utility.datasets import DriftStream

>>> dataset = DriftStream(n_samples=2000, n_features=5, n_drifts=1, kind="sudden", seed=0)

>>> for x, y in dataset.stream():
...     print(x.to_dict())
...     print(y)
...     break
{'x0': 0.00889176732883129, 'x1': 0.7559062648510446, 'x2': -2.788269695138754, 'x3': 0.0168051027297742, 'x4': 1.9630566360240487}
0

Now let's run the model on the dataset in a streaming fashion. We sequentially interleave predictions and model updates. Meanwhile, we update a performance metric to see how well the model is doing.

>>> from dense_armor.utility.learn.online_classifiers import OnlineGaussianNB
>>> from dense_armor.utility.metrics import Accuracy

>>> model = OnlineGaussianNB()

>>> metric = Accuracy()

>>> for x, y in dataset.stream():
...     y_pred = model.predict_one(x)
...     if y_pred is not None:
...         metric.update(y, y_pred)
...     model.learn_one(x, y)

>>> metric
Accuracy(n=1999, value=0.9989994997498749)

Of course, this is just a contrived example. Check the getting started section of the documentation for a more thorough tutorial.

On a robot

A joint torque stream from SyntheticArm (real Panda URDF, real rigid-body dynamics) carries a 1e6 spike at sample 50. A rate-limited follower caps the applied jump at max_vel per step, so a downstream controller never sees the spike:

from pathlib import Path
import numpy as np
from dense_armor.utility.datasets import SyntheticArm
from dense_armor.utility.control.rate_limiter import rate_limited_follower

ds = SyntheticArm(
    Path("test/fixtures/urdf/panda.urdf"),
    period_s=1.0, rate_hz=50.0, n_cycles=2,
    fault_at_s=None, fault=None, seed=0,
)
tau = np.array([float(sig["tau_1"]) for sig, _ in ds.stream()])
tau[50] = 1e6

safe = rate_limited_follower(tau, max_vel=2.0, max_accel=1.0)
print(round(float(np.max(np.abs(tau))), 1), round(float(np.max(np.abs(safe))), 1))

1000000.0 272.2

RigidBodyModel loads dynamics from the same URDF (.xacro and <mimic> joints included), quintic_trajectory generates a minimum-jerk path, and cbf_safety_filter enforces a spatial barrier around an obstacle.

Install

pip install dense-armor                 # core: numpy + jax
pip install "dense-armor[vision]"       # + camera (OpenCV), image folder (Pillow), in-memory
pip install "dense-armor[ros]"          # + rosbag readers
pip install "dense-armor[audio,data]"   # + WAV, HDF5, NetCDF
pip install "dense-armor[mcp]"          # + MCP server for LLM agents
pip install "dense-armor[quantum]"      # + Dense-Evolution (NISQ simulator)

Works on Python 3.10+. JAX is the backend for every estimator.

Features

Dense-Armor provides online implementations of the following families of algorithms:

• Linear models, with a wide array of optimizers
• Decision trees (including FIMT-DD regression model trees), online forests (adaptive random forest, aggregated Mondrian forests, online extra trees) and rule sets (adaptive model rules)
• Naive Bayes, nearest neighbours, multiclass and multi-output wrappers, conjugate distributions
• Ensembles (online bagging and boosting, exponentially weighted average, voting, stacking)
• Bandits (epsilon-greedy, UCB, Thompson sampling, Bayes-UCB, Exp3, LinUCB, offline replay)
• Active learning (random, fixed, variable and randomised uncertainty with a labelling budget)
• Factorization machines (plain, field-aware, field-weighted, higher-order) and recommenders (baseline, biased and plain matrix factorization, sliding DFT, skyline)
• Clustering
• Anomaly detection (including the local outlier factor)
• Drift detection
• Time series (AR, VAR, Kalman, adaptive Kalman, cycle residual)
• Online classifiers
• Online dynamics
• Calibration and metric learning
• Imbalanced learning
• Vision (video files, frame features, patches, vocabulary, online reduction, motion, tracking, registration, dense flow)
• Robot control (rate limits, control barrier functions, trajectories, kinematic tracking)
• Robot dynamics (URDF, passivity + CBF controllers)
• Shielding (1D series cleanup, input/output shield, per-point routing)
• Finance pipelines: nine pipelines for markets, fraud, intrusion and credit scoring, each page opening with the question it answers
• Finance: Regime: the regime page.
• Finance: Drift vs noise: the drift vs noise page.
• Finance: Portfolio: the portfolio page.
• Finance: Order book: the order book page.
• Finance: Stress: the stress page.
• Finance: Streaming: the streaming page.
• Finance: Timing: the timing page.
• Offline learning: fit feeds a whole dataset to any online algorithm, and the batch tree, the bagging and the text vectorizer learn from all the rows at once

Dense-Armor also provides other online utilities:

• Feature extraction and selection
• Online statistics and sketches
• Metrics for streams and robots
• Preprocessing, with a text vectorizer that ranks documents by TF-IDF and cosine similarity
• Streams (CSV, arrays, rosbag, frame folders, merge by time, shuffle)
• Built-in datasets
• Progressive model validation
• Model pipelines
• LLM bridge (embeddings as features, estimators as JSON tools)
• Checks (check_estimator, p99 budget, memory growth, clone, pickle, state dict, roc_auc)
• Core engine (DynamicAICodegen JIT compiler, ImageChunker, UniversalMemoryGuard, AdaptiveSignalStabilizer, AIHardwareProfiler, StochasticAdversarialNoise)

Check out the API for a comprehensive overview.

Should I be using Dense-Armor?

Batch learning does the job for many problems, and Dense-Armor covers it with fit and the batch versions. An online approach fits when:

• you want a model that learns from new data without revisiting past data
• you want a model that is robust to concept drift
• the production context is event-based, not batch-based, and you want the code to look like it
• you want the model to be protected from corrupted input, NaN, spikes, or slow drift without retraining it
• you work with a real robot and need command-side safety in the same library that learns the model

Some specifics:

• It focuses on clarity and user experience, more than on raw speed.
• It runs on JAX, so the same code runs on CPU, GPU or TPU.
• It plays nicely with the rest of Python's ecosystem: numpy in, numpy out.

Useful links

• Documentation
• Getting started
• API reference
• Changelog
• Package releases
• Sister project (Dense-Evolution)
• DOI

Contributing

Contributions are welcome. The library is built to be extended one estimator at a time, following the same interface (learn_one / predict_one / transform_one) and the same checks (dense_armor.checks). Code style is checked with ruff check dense_armor, configured in pyproject.toml.

Citation

@software{pennacchio_dense_armor,
  author    = {Pennacchio, Salvatore},
  title     = {Dense-Armor: Robot-AI Online Shielding \\& Learning},
  year      = 2026,
  publisher = {Zenodo},
  doi       = {10.5281/zenodo.23527280}
}

License

GNU Affero General Public License v3.0 or later. See LICENSE. Releases up to 1.1.32 were published under the Business Source License 1.1: LICENSE-BUSL-1.1-until-1.1.32.md. A commercial licence is available on request.

© 2026 Salvatore Pennacchio <jtatopenn@libero.it>

Twin project of Dense-Evolution (NISQ quantum circuit simulator).

Speed

The per-sample cost of the main estimators, measured by benchmarks/speed.py on an Intel Xeon 2.20 GHz with 2 cores, 20 seeds, 2000 samples per seed, first 200 discarded. Full table and machine in benchmarks/speed_log.md.

The robot-side components stay inside a 1 kHz control-loop budget (1000 µs) at the median: 36.5 µs for the rate-limited follower, 0.9 µs for the control barrier function filter, 8.1 µs for the kinematic tracking controller, 66 µs for the rigid-body mass matrix and 55 µs for the gravity forces (the last two through jax.jit).

Acknowledgements

Dense-Armor takes inspiration from River (Montiel et al., 2020, arXiv:2012.04740), the online machine learning library.

• Drones: Actuator fault.
• Drones: Sensor consistency.
• Drones: Propeller health: is a propeller damaged?.
• Drones: Battery endurance: how many minutes of flight are left, and how sure?.
• Drones: Safety filter: is the next move safe?.
• Drones: Link health: is the radio link about to fail?.
• Drones: Visual landing: is the pad where I think it is, and is the camera moving?.
• Drones: Static vs online: a CART tree and an online Hoeffding tree on the same stream.
• Drones: Start here: a drone and a board.
• Drones: ArduPilot against PX4.
• Drones: Jetson power: how much does the power mode change the time per sample?.
• Drones: Jetson energy: the joules per 1000 samples of the online and batch pipelines, and one command to measure them on a board.