grubeta 0.1.1

GRU-based Dynamic Beta Estimation for Time-Varying Systematic Risk

GRU Dynamic Beta

GRU Dynamic Beta is a Python library for estimating time-varying systematic risk (beta) using Gated Recurrent Unit neural networks within the CAPM framework.

Key Features

• GRU-based estimation: Captures complex temporal patterns in beta dynamics
• Walk-forward validation: Prevents lookahead bias with proper out-of-sample testing
• Composite loss function: Balances prediction accuracy, beta stability, and alpha sparsity
• Flexible input modes: Use simple returns or full feature engineering
• Built-in evaluation: Comprehensive metrics and benchmark comparisons
• Production-ready: GPU support, model persistence, and extensive documentation

Installation

Basic Installation

pip install grubeta

Full Installation (with technical analysis features)

pip install grubeta[full]

Development Installation

git clone https://github.com/aslmylmz/grubeta.git
cd grubeta
pip install -e ".[dev]"

Quick Start

Simple Usage (Returns Only)

The simplest way to estimate dynamic beta using only stock and market returns:

import pandas as pd
from grubeta import DynamicBeta

# Load your data
stock_returns = pd.read_csv('stock_data.csv')['return']
market_returns = pd.read_csv('market_data.csv')['return']

# Estimate dynamic beta
model = DynamicBeta(lookback=60)
results = model.fit_predict(stock_returns, market_returns)

# View results
print(results[['beta', 'alpha']].dropna().describe())

# Plot beta evolution
model.plot_beta(results, title='Dynamic Beta - AAPL')

Advanced Usage (With Features)

For better results, use the full preprocessing pipeline:

from grubeta import DynamicBeta, DataPreprocessor, FeatureConfig

# Configure feature engineering
config = FeatureConfig(
    include_technicals=True,
    include_macro=True,
    lag_features=True  # Critical for preventing lookahead bias
)

# Prepare features
preprocessor = DataPreprocessor(config)
features = preprocessor.prepare(
    stock_df=stock_ohlcv,    # OHLCV data
    market_df=market_ohlcv,  # Market index OHLCV
    macro_df=macro_data      # Macroeconomic indicators
)

# Estimate with features
model = DynamicBeta(
    lookback=90,
    lambda_beta=0.05,   # Beta stability weight
    lambda_alpha=0.5,   # Alpha sparsity weight
)
results = model.fit_predict(**features)

Model Evaluation

from grubeta import BetaEvaluator
from grubeta.utils import rolling_ols_beta

# Create evaluator
evaluator = BetaEvaluator(output_dir='./results')

# Compute benchmark
ols_beta = rolling_ols_beta(
    results['stock_return'], 
    results['market_return'],
    window=252
)

# Compare models
comparison = evaluator.compare_models(
    {
        'GRU': results['beta'].values,
        'Rolling OLS': ols_beta,
    },
    results['stock_return'].values,
    results['market_return'].values,
)
print(comparison)

Architecture

The GRU Dynamic Beta model uses a dual-pathway architecture:

Market Features ──→ [GRU] ──→ Beta(t)
                              ↓
                    R_stock = α + β × R_market
                              ↑
Stock Features ──→ [GRU] ──→ Alpha(t)

Loss Function

The composite loss balances three objectives:

1. Accuracy: Huber loss on return predictions
2. Stability: L2 penalty on beta changes (temporal smoothness)
3. Sparsity: L1 penalty on alpha (CAPM compliance)

L = L_accuracy + λ_β × L_stability + λ_α × L_sparsity

Configuration

Model Hyperparameters

Parameter	Default	Description
lookback	90	Sequence length for GRU input
initial_train_size	500	Samples for initial training
wf_step_size	126	Walk-forward step size
learning_rate	1e-4	Adam optimizer learning rate
gru_units	128	GRU hidden units
dropout_rate	0.2	Dropout regularization
lambda_beta	0.05	Beta stability weight
lambda_alpha	0.5	Alpha sparsity weight

Feature Configuration

from grubeta import FeatureConfig

config = FeatureConfig(
    lag_features=True,        # Prevent lookahead bias
    include_technicals=True,  # RSI, MACD, ADX, etc.
    include_macro=True,       # Macro indicators
    include_volume=True,      # Volume-based features
    include_calendar=True,    # Day of week, month end, etc.
    ma_windows=[5, 10, 20, 50, 100, 200],
    volatility_windows=[5, 10, 20, 60],
)

API Reference

Core Classes

DynamicBeta

Main estimator class for GRU-based dynamic beta estimation.

DynamicBeta(
    config: DynamicBetaConfig = None,
    lookback: int = 90,
    lambda_beta: float = 0.05,
    lambda_alpha: float = 0.5,
    **kwargs
)

Methods:

• fit(stock_returns, market_returns, ...) - Fit the model
• predict(stock_returns, market_returns, ...) - Predict beta for new data
• fit_predict(stock_returns, market_returns, ...) - Fit and predict with walk-forward validation
• save(path) - Save model to disk
• load(path) - Load model from disk
• plot_beta(results, ...) - Visualize beta trajectory

DataPreprocessor

Feature engineering pipeline with lookahead bias prevention.

DataPreprocessor(config: FeatureConfig = None)

Methods:

• prepare_simple(stock_returns, market_returns, ...) - Minimal preprocessing
• prepare(stock_df, market_df, macro_df) - Full feature engineering

BetaEvaluator

Evaluation suite for dynamic beta estimates.

BetaEvaluator(output_dir: str = None)

Methods:

• evaluate(betas, stock_returns, market_returns, ...) - Comprehensive evaluation
• compare_models(betas_dict, stock_returns, market_returns) - Model comparison

Utility Functions

from grubeta.utils import (
    validate_no_lookahead,  # Check for lookahead bias
    rolling_ols_beta,       # Benchmark beta calculation
    align_series,           # Align multiple time series
    compute_information_coefficient,  # Calculate IC
)

Input Data Formats

Simple Mode (Returns Only)

# Pandas Series or NumPy arrays
stock_returns = df['close'].pct_change()
market_returns = market_df['close'].pct_change()

Full Mode (OHLCV + Macro)

Stock/Market OHLCV DataFrame:

| Date       | Open   | High   | Low    | Close  | Volume    |
|------------|--------|--------|--------|--------|-----------|
| 2020-01-02 | 100.00 | 101.50 | 99.50  | 101.00 | 1000000   |
| 2020-01-03 | 101.00 | 102.00 | 100.50 | 101.50 | 1200000   |

Macro DataFrame (optional):

| Date       | vix    | fed_rate | unemployment | ...  |
|------------|--------|----------|--------------|------|
| 2020-01-02 | 12.5   | 1.75     | 3.6          | ...  |
| 2020-01-03 | 13.2   | 1.75     | 3.6          | ...  |

Lookahead Bias Prevention

GRU Dynamic Beta implements strict lookahead bias prevention:

1. Feature Lagging: All features are lagged by 1 day (configurable)
2. Walk-Forward Validation: Model only sees historical data at each prediction point
3. Expanding Window Scaling: Scalers are refit on expanding historical data only
4. Built-in Validation: validate_no_lookahead() function to verify

from grubeta.utils import validate_no_lookahead

# Check for lookahead bias
passed = validate_no_lookahead(
    results['beta'].values,
    results['stock_return'].values,
    results['market_return'].values,
    initial_size=500
)
# Output:
#   ✓ Beta correlation with return t+1: 0.023
#   ✓ Beta correlation with return t+5: 0.018
#   ✓ Beta correlation with return t+10: 0.012
#   ✓ Beta correlation with return t+20: 0.008

Examples

Portfolio Hedging

from grubeta import DynamicBeta
from grubeta.utils import beta_to_hedge_ratio

# Estimate beta
model = DynamicBeta()
results = model.fit_predict(stock_returns, market_returns)

# Current beta
current_beta = results['beta'].iloc[-1]

# Calculate hedge ratio
stock_position = 100_000  # $100k position
spy_price = 450  # SPY price

hedge = beta_to_hedge_ratio(current_beta, stock_position, spy_price)
print(f"To hedge: short {hedge:.0f} shares of SPY")

Multi-Asset Analysis

from grubeta import DynamicBeta, BetaEvaluator

stocks = ['AAPL', 'GOOGL', 'MSFT', 'AMZN']
results = {}

model = DynamicBeta(lookback=60)

for stock in stocks:
    stock_ret = load_returns(stock)
    results[stock] = model.fit_predict(stock_ret, market_returns)
    
# Compare beta dynamics
import matplotlib.pyplot as plt

fig, ax = plt.subplots(figsize=(12, 6))
for stock, res in results.items():
    ax.plot(res['date'], res['beta'], label=stock)
ax.legend()
ax.set_title('Dynamic Beta Comparison')
plt.show()

Comparison with Other Methods

Method	Time-Varying	Captures Non-linearity	Lookahead Free	Walk-Forward
Static OLS	❌	❌	✅	N/A
Rolling OLS	✅	❌	✅	✅
EWMA	✅	❌	✅	✅
Kalman Filter	✅	❌	✅	✅
DCC-GARCH	✅	Partial	✅	✅
GRU Dynamic Beta	✅	✅	✅	✅

Citation

If you use GRU Dynamic Beta in your research, please cite:

@software{grubeta2026,
  author = {Yılmaz, Ahmet Selim},
  title = {GRU Dynamic Beta: Neural Network-Based Time-Varying Systematic Risk Estimation},
  year = {2026},
  url = {https://github.com/aslmylmz/grubeta}
}

Related Work

• arch - GARCH models
• pykalman - Kalman Filter
• statsmodels - Statistical models
• ta - Technical Analysis library

Contributing

Contributions are welcome! Please see CONTRIBUTING.md for guidelines.

License

MIT License - see LICENSE for details.

Changelog

See CHANGELOG.md for version history.