cplx-mfa 0.1.0

Complex-valued mixture of factor analyzers with a scikit-learn-like API.

cplx-mfa

Complex-valued mixture of factor analyzers with a scikit-learn-like API.

cplx-mfa provides an estimator for fitting mixture of factor analyzers (MFA) models to complex-valued data using expectation-maximization (EM). The model uses circularly symmetric complex Gaussian components with low-rank covariance structure, making it useful for high-dimensional signal processing problems where full covariance Gaussian mixtures can be too expensive or statistically inefficient.

Parts of the implementation are derived from the original mofa package and extended with complex-valued modeling support, modern packaging, improved naming, validation, reproducible initialization, and functional tests.

✨ Highlights

• Complex-valued mixture of factor analyzers for data in complex vector spaces
• Low-rank covariance structure via component-wise factor loading matrices
• Circularly symmetric complex Gaussian components
• scikit-learn-like estimator API with fit, predict, predict_proba, and sample
• Optional isotropic PPCA-style noise model
• Optional shared diagonal noise variances across components
• Sampling from fitted complex-valued MFA models
• Fitted parameters exposed with trailing-underscore names
• Modern Python packaging with pyproject.toml, uv, pytest, and ruff

📌 Citation

If you use cplx-mfa in academic work, please cite the package directly:

@software{fesl_cplx_mfa,
  author = {Fesl, Benedikt},
  title = {{cplx-mfa}: Complex-valued mixture of factor analyzers},
  year = {2026},
  url = {https://github.com/benediktfesl/cplx-mfa},
  version = {0.1.0}
}

Plain-text citation:

B. Fesl, cplx-mfa: Complex-valued mixture of factor analyzers, version 0.1.0. Available: https://github.com/benediktfesl/cplx-mfa

📦 Installation

Install from PyPI:

pip install cplx-mfa

or with uv:

uv add cplx-mfa

For development, clone the repository and install the development environment:

git clone https://github.com/benediktfesl/cplx-mfa.git
cd cplx-mfa
uv sync --group dev

🚀 Quick Start

import numpy as np

from cplx_mfa import ComplexMFA

rng = np.random.default_rng(0)

X = (
    rng.normal(size=(1_000, 8))
    + 1j * rng.normal(size=(1_000, 8))
) / np.sqrt(2.0)

model = ComplexMFA(
    n_components=4,
    latent_dim=2,
    random_state=0,
    max_iter=100,
    verbose=False,
)

model.fit(X)

labels = model.predict(X)
responsibilities = model.predict_proba(X)

samples, component_labels = model.sample(
    n_samples=100,
    rng=np.random.default_rng(1),
)

The estimator follows the usual pattern: model configuration is passed to the constructor, and fit(X) receives the data.

🧩 Model Structure

A mixture of factor analyzers represents each mixture component with a low-rank covariance structure:

covariance = loadings @ loadingsᴴ + diagonal_noise

This is useful when the feature dimension is large but the dominant component-wise variation is approximately low-dimensional.

The fitted attributes are:

Attribute	Description
weights_	Mixture weights of shape (n_components,).
means_	Component means of shape (n_components, n_features).
loadings_	Factor loading matrices of shape (n_components, n_features, latent_dim).
covariances_	Full implied covariance matrices of shape (n_components, n_features, n_features).
precisions_	Inverse covariance matrices of shape (n_components, n_features, n_features).
noise_variances_	Diagonal noise variances of shape (n_components, n_features).
lower_bound_history_	EM lower-bound values collected during fitting.

🧠 Estimator API

The main class is:

from cplx_mfa import ComplexMFA

Core methods:

Method	Description
fit(X)	Fit the complex-valued MFA model.
predict(X)	Predict the most likely component for each sample.
predict_proba(X)	Return posterior component probabilities.
sample(n_samples=1, rng=None)	Draw samples from the fitted mixture model.

Constructor parameters:

Parameter	Description
n_components	Number of mixture components.
latent_dim	Latent dimensionality of each factor analyzer.
ppca	If True, use one isotropic noise variance per component.
lock_psis	If True, use shared diagonal noise variances across components.
rs_clip	Lower clipping value for responsibilities during EM.
max_condition_number	Scaling factor used for random loading initialization.
max_iter	Maximum number of EM iterations.
tol	Relative convergence tolerance.
random_state	Integer seed or NumPy random generator used for initialization.
verbose	If True, print EM progress.

🔁 Sampling

Samples are generated component-wise and returned grouped by component. The returned labels follow the same order.

samples, labels = model.sample(
    n_samples=100,
    rng=np.random.default_rng(1),
)

This means labels is sorted by component group rather than shuffled randomly. This behavior is intentional and documented so that generated samples can be inspected component by component.

🔬 PPCA-Style Components

Set ppca=True to constrain each component to use an isotropic diagonal noise variance:

model = ComplexMFA(
    n_components=4,
    latent_dim=2,
    ppca=True,
    random_state=0,
)

model.fit(X)

This gives a probabilistic PCA-style covariance structure per mixture component.

🔒 Shared Noise Variances

Set lock_psis=True to enforce shared diagonal noise variances across all mixture components:

model = ComplexMFA(
    n_components=4,
    latent_dim=2,
    lock_psis=True,
    random_state=0,
)

model.fit(X)

This can be useful when all mixture components are expected to share the same residual noise floor.

📚 Research Background

This implementation was developed in the context of complex-valued generative modeling for wireless channel estimation and related signal processing applications.

The results of the following work are, in parts, based on the complex-valued MFA implementation:

• B. Fesl, N. Turan, and W. Utschick, “Low-Rank Structured MMSE Channel Estimation with Mixtures of Factor Analyzers,” 57th Asilomar Conference on Signals, Systems, and Computers, 2023.
  [IEEE] [arXiv]

🧪 Development

Install the development environment with uv:

uv sync --group dev

Run tests:

uv run pytest

Run linting:

uv run ruff check .

Format code:

uv run ruff format .

Run the example:

uv run python examples/cplx_mfa_example.py

Build the package:

uv run python -m build

✅ Test Coverage

The test suite covers:

• package imports
• fitting and fitted attribute shapes
• prediction and responsibility normalization
• sampling behavior
• grouped sample labels
• validation behavior
• unfitted-estimator behavior
• reproducibility with fixed random_state
• EM lower-bound history
• utility functions for complex-valued data handling
• example execution

📄 License

This project is licensed under the BSD 3-Clause License.

The implementation contains code derived from the original mofa package, which is MIT-licensed. Attribution and provenance are retained in NOTICE.