atcnd 0.2.0

Adaptive Topic and Cluster Number Determination via structured search

ATCND

Adaptive Topic and Cluster Number Determination via Structured Search over Sliding Ranges.

ATCND is a model-agnostic framework that determines the optimal number of topics (for LDA/NMF) or clusters (for K-Means) by treating K selection as a structured search problem over a user-specified integer range. Instead of exhaustive grid search requiring O(K_max - K_min) model evaluations, ATCND applies binary search, golden section search, or ternary search to achieve O(log(K_max - K_min)) evaluations while matching or exceeding the quality of grid search.

Key Features

• Four search strategies: binary, golden section, ternary, grid
• Three model families: LDA, NMF, K-Means
• Five quality metrics: silhouette, coherence, perplexity, reconstruction error, combined
• Returns a ranked set of top-K candidates (handles plateaus, ties, multiple optima)
• 60--80% fewer model evaluations than grid search
• CLI and Python API

Installation

pip install atcnd

From source:

git clone https://github.com/CodeOfMe/ATCND.git
cd ATCND
pip install .

Quick Start

Python API

from atcnd import ATCNDConfig, atcnd_search, print_topics

# K-Means on numeric data
from sklearn.datasets import make_blobs
X, _ = make_blobs(n_samples=1000, n_features=50, centers=8, random_state=42)

config = ATCNDConfig(
    k_min=2, k_max=30,
    model_type="kmeans",
    search_strategy="binary",
    metric="silhouette",
    n_candidates=3,
)
result = atcnd_search(X=X, config=config)

print(f"Optimal K: {result.optimal_k}")
print(f"Best score: {result.optimal_score:.4f}")
print(f"Top candidates: {result.candidate_ks}")
print(f"Evaluations: {len(result.search_history)}")

Text data (LDA/NMF)

from atcnd import ATCNDConfig, atcnd_search

texts = ["your document texts here"] * 100

# NMF with coherence metric
config = ATCNDConfig(
    k_min=2, k_max=20,
    model_type="nmf",
    search_strategy="binary",
    metric="coherence",
)
result = atcnd_search(texts=texts, config=config)

CLI

# Search with K-Means on synthetic data
atcnd search --model kmeans --strategy binary --k-min 2 --k-max 30

# Search with NMF
atcnd search --model nmf --strategy golden_section --metric silhouette

# JSON output
atcnd search --model kmeans --json

# Run benchmarks
atcnd benchmark --dataset blobs --k-min 2 --k-max 30

Search Strategies

Strategy	Complexity	Best for	Evaluations (K in [2,30])
Grid	O(N)	Baseline comparison	29
Binary	O(log N)	Unimodal objectives	~6
Golden Section	O(log_phi N)	General objectives	~7
Ternary	O(log_{1.5} N)	Multi-step objectives	~8

Quality Metrics

Metric	LDA	NMF	K-Means	Description
Silhouette	Yes	Yes	Yes	Inter-cluster separation vs intra-cluster cohesion
Coherence (c_v)	Yes	Yes	No	Semantic coherence of top topic words
Perplexity	Yes	No	No	Negative log-likelihood per word
Reconstruction	No	Yes	Yes	Frobenius norm / inertia
Combined	Yes	Yes	No	0.5 * silhouette + 0.5 * coherence

Multiple Optima

K is a discrete integer parameter. Multiple values of K may achieve the same or nearly the same quality score due to:

• Exact equality in f(K) at different K values
• Plateaus where nearby K values produce identical scores
• Multiple local maxima from different data partitioning granularities

ATCND returns candidate_ks (a ranked list) and candidate_scores alongside the single best optimal_k, enabling users to make informed decisions based on domain knowledge.

Development

# Install in development mode
pip install -e ".[dev]"

# Run tests
python -m pytest tests/

# Format code
black src/atcnd/ tests/

# Lint code
ruff check src/atcnd/ tests/

License

GNU General Public License v3.0 (GPLv3)