TP: Recurrent Neural Networks for Time Series Prediction

Author

Remi Genet

Published

2025-04-03

!pip install numpy keras jax matplotlib scikit-learn yfinance
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WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv

Data Preparation

First, let’s prepare our dataset using yfinance to get historical stock data.

import os
os.environ["KERAS_BACKEND"] = "jax"  # Environment variable need to be set prior to importing keras, default is tensorflow
import yfinance as yf
import numpy as np
import pandas as pd
from sklearn.preprocessing import StandardScaler
from sklearn.model_selection import train_test_split
from sklearn.linear_model import LinearRegression
from sklearn.metrics import r2_score
import keras
from keras import layers
import matplotlib.pyplot as plt

# Download data
ticker = "^GSPC"
data = yf.download(ticker, start="2000-01-01", end="2024-01-01")

# Compute absolute returns (volatility proxy)
returns = np.abs(data['Close'].pct_change())
returns = returns.dropna()

def create_sequences(data, seq_length, horizon):
    """Create sequences for training"""
    X, y = [], []
    for i in range(len(data) - seq_length - horizon + 1):
        X.append(data[i:(i + seq_length)])
        y.append(data[(i + seq_length):(i + seq_length + horizon)])
    return np.array(X), np.squeeze(np.array(y))

# Parameters
sequence_length = 200
prediction_horizon = 1

# Create sequences
X, y = create_sequences(returns.values, sequence_length, prediction_horizon)

# Split data
X_train, X_test, y_train, y_test = train_test_split(
    X, y, test_size=0.2, shuffle=False
)

early_stopping_callback = lambda : keras.callbacks.EarlyStopping(
    monitor="val_loss",
    min_delta=0.00001,
    patience=10,
    mode="min",
    restore_best_weights=True,
    start_from_epoch=6,
)
lr_callback = lambda : keras.callbacks.ReduceLROnPlateau(
    monitor="val_loss",
    factor=0.25,
    patience=5,
    mode="min",
    min_delta=0.00001,
    min_lr=0.000025,
    verbose=0,
)
callbacks = lambda : [early_stopping_callback(), lr_callback(), keras.callbacks.TerminateOnNaN()]
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Question 1: Simple LSTM Model

Implement a single-layer LSTM of 100 units, that only return last hidden state, followed by a linear Dense layer model using Keras Sequential API to predict the next value. Compare its performance with a simple linear regression model, and a 3 layer MLP of 100 units with relu activation.

37/37 ━━━━━━━━━━━━━━━━━━━━ 1s 7ms/step  
37/37 ━━━━━━━━━━━━━━━━━━━━ 1s 11ms/step 
LSTM R² score: 0.3068
MLP R² score: 0.1371
Linear Regression R² score: 0.2458

Question 2: GRU Implementation

Now implement a similar model using GRU and compare its performance.

37/37 ━━━━━━━━━━━━━━━━━━━━ 0s 8ms/step  
GRU R² score: 0.2700

Question 3: Two-Layer Models

Implement and compare two-layer versions of both LSTM and GRU models.

37/37 ━━━━━━━━━━━━━━━━━━━━ 1s 12ms/step 
37/37 ━━━━━━━━━━━━━━━━━━━━ 1s 12ms/step 
Double LSTM R² score: 0.3084
Double GRU R² score: 0.2510

Question 4: Custom LSTM Implementation

Implement a custom LSTM layer by writing out all the equations. Here’s the mathematical formulation you need to implement:

  1. Input gate: i_t = σ(W_i·[h_{t-1}, x_t] + b_i)
  2. Forget gate: f_t = σ(W_f·[h_{t-1}, x_t] + b_f)
  3. Cell state: c̃_t = tanh(W_c·[h_{t-1}, x_t] + b_c)
  4. Output gate: o_t = σ(W_o·[h_{t-1}, x_t] + b_o)
  5. New cell state: c_t = f_t ∗ c_{t-1} + i_t ∗ c̃_t
  6. Hidden state: h_t = o_t ∗ tanh(c_t)

Hint: Split the code in two, implement a method that do one step only, while the call function iterate over the sequence and uses it

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