Graph Convolutional Network (#1163)

* Implement GCN model architecture

* Comments added to GCN example

* test added

* match random seed with PR screenshot

* Update index.rst

Author: JoseLuisC99

Diff for: .gitignore

@@ -12,6 +12,7 @@ snli/results
 word_language_model/model.pt
 fast_neural_style/saved_models
 fast_neural_style/saved_models.zip
+gcn/cora/
 docs/build
 docs/venv
 

Diff for: docs/source/index.rst

@@ -169,3 +169,11 @@ experiment with PyTorch.
 
     `GO TO EXAMPLE <https://github.com/pytorch/examples/tree/main/mnist_forward_forward>`__ :opticon:`link-external` 
 
+    ---
+
+    Graph Convolutional Network
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+    This example implements the `Semi-Supervised Classification with Graph Convolutional Networks <https://arxiv.org/pdf/1609.02907.pdf>`__ paper on the CORA database.
+
+    `GO TO EXAMPLE <https://github.com/pytorch/examples/blob/main/gcn>`__ :opticon:`link-external` 

Diff for: gcn/README.md

@@ -0,0 +1,39 @@
+# Graph Convolutional Network
+
+This repository contains an implementation of Graph Convolutional Networks (GCN) based on the paper "Semi-Supervised Classification with Graph Convolutional Networks" by Thomas N. Kipf and Max Welling.
+
+## Overview
+This project implements the GCN model proposed in the paper for semi-supervised node classification on graph-structured data. GCN leverages graph convolutions to aggregate information from neighboring nodes and learn node representations for downstream tasks. The implementation provides a flexible and efficient GCN model for graph-based machine learning tasks.
+
+# Requirements
+- Python 3.7 or higher
+- PyTorch 2.0 or higher
+- Requests 2.31 or higher
+- NumPy 1.24 or higher
+
+
+# Installation
+```bash
+pip install -r requirements.txt
+python main.py
+```
+
+# Dataset
+The implementation includes support for the Cora dataset, a standard benchmark dataset for graph-based machine learning tasks. The Cora dataset consists of scientific publications, where nodes represent papers and edges represent citation relationships. Each paper is associated with a binary label indicating one of seven classes. The dataset is downloaded, preprocessed and ready to use.
+
+## Model Architecture
+The GCN model architecture follows the details provided in the paper. It consists of multiple graph convolutional layers with ReLU activation, followed by a final softmax layer for classification. The implementation supports customizable hyperparameters such as the number of hidden units, the number of layers, and dropout rate.
+
+## Usage
+To train and evaluate the GCN model on the Cora dataset, use the following command:
+```bash
+python train.py --epochs 200 --lr 0.01 --l2 5e-4 --dropout-p 0.5 --hidden-dim 16 --val-every 20 --include-bias False --no-cuda False
+```
+
+# Results
+The model achieves a classification accuracy of 82.5% on the test set of the Cora dataset after 200 epochs of training. This result is comparable to the performance reported in the original paper. However, the results can vary due to the randomness of the train/val/test split.
+
+References
+Thomas N. Kipf and Max Welling. "Semi-Supervised Classification with Graph Convolutional Networks." Link to the paper
+
+Original paper repository: [https://github.com/tkipf/gcn](https://github.com/tkipf/gcn)

Diff for: gcn/main.py

@@ -0,0 +1,262 @@
+import os
+import time
+import requests
+import tarfile
+import numpy as np
+import argparse
+
+import torch
+from torch import nn
+import torch.nn.functional as F
+from torch.optim import Adam
+
+
+class GraphConv(nn.Module):
+    """
+        Graph Convolutional Layer described in "Semi-Supervised Classification with Graph Convolutional Networks".
+
+        Given an input feature representation for each node in a graph, the Graph Convolutional Layer aims to aggregate
+        information from the node's neighborhood to update its own representation. This is achieved by applying a graph
+        convolutional operation that combines the features of a node with the features of its neighboring nodes.
+
+        Mathematically, the Graph Convolutional Layer can be described as follows:
+
+            H' = f(D^(-1/2) * A * D^(-1/2) * H * W)
+
+        where:
+            H: Input feature matrix with shape (N, F_in), where N is the number of nodes and F_in is the number of 
+                input features per node.
+            A: Adjacency matrix of the graph with shape (N, N), representing the relationships between nodes.
+            W: Learnable weight matrix with shape (F_in, F_out), where F_out is the number of output features per node.
+    """
+    def __init__(self, input_dim, output_dim, use_bias=False):
+        super(GraphConv, self).__init__()
+
+        # Initialize the weight matrix W (in this case called `kernel`)
+        self.kernel = nn.Parameter(torch.Tensor(input_dim, output_dim))
+        nn.init.xavier_normal_(self.kernel) # Initialize the weights using Xavier initialization
+
+        # Initialize the bias (if use_bias is True)
+        self.bias = None
+        if use_bias:
+            self.bias = nn.Parameter(torch.Tensor(output_dim))
+            nn.init.zeros_(self.bias) # Initialize the bias to zeros
+
+    def forward(self, input_tensor, adj_mat):
+        """
+        Performs a graph convolution operation.
+
+        Args:
+            input_tensor (torch.Tensor): Input tensor representing node features.
+            adj_mat (torch.Tensor): Adjacency matrix representing graph structure.
+
+        Returns:
+            torch.Tensor: Output tensor after the graph convolution operation.
+        """
+
+        support = torch.mm(input_tensor, self.kernel) # Matrix multiplication between input and weight matrix
+        output = torch.spmm(adj_mat, support) # Sparse matrix multiplication between adjacency matrix and support
+        # Add the bias (if bias is not None)
+        if self.bias is not None:
+            output = output + self.bias
+
+        return output
+
+
+class GCN(nn.Module):
+    """
+    Graph Convolutional Network (GCN) as described in the paper `"Semi-Supervised Classification with Graph 
+    Convolutional Networks" <https://arxiv.org/pdf/1609.02907.pdf>`.
+
+    The Graph Convolutional Network is a deep learning architecture designed for semi-supervised node 
+    classification tasks on graph-structured data. It leverages the graph structure to learn node representations 
+    by propagating information through the graph using graph convolutional layers.
+
+    The original implementation consists of two stacked graph convolutional layers. The ReLU activation function is 
+    applied to the hidden representations, and the Softmax activation function is applied to the output representations.
+    """
+    def __init__(self, input_dim, hidden_dim, output_dim, use_bias=True, dropout_p=0.1):
+        super(GCN, self).__init__()
+
+        # Define the Graph Convolution layers
+        self.gc1 = GraphConv(input_dim, hidden_dim, use_bias=use_bias)
+        self.gc2 = GraphConv(hidden_dim, output_dim, use_bias=use_bias)
+
+        # Define the dropout layer
+        self.dropout = nn.Dropout(dropout_p)
+
+    def forward(self, input_tensor, adj_mat):
+        """
+        Performs forward pass of the Graph Convolutional Network (GCN).
+
+        Args:
+            input_tensor (torch.Tensor): Input node feature matrix with shape (N, input_dim), where N is the number of nodes
+                and input_dim is the number of input features per node.
+            adj_mat (torch.Tensor): Adjacency matrix of the graph with shape (N, N), representing the relationships between
+                nodes.
+
+        Returns:
+            torch.Tensor: Output tensor with shape (N, output_dim), representing the predicted class probabilities for each node.
+        """
+
+        # Perform the first graph convolutional layer
+        x = self.gc1(input_tensor, adj_mat)
+        x = F.relu(x) # Apply ReLU activation function
+        x = self.dropout(x) # Apply dropout regularization
+
+        # Perform the second graph convolutional layer
+        x = self.gc2(x, adj_mat)
+
+        # Apply log-softmax activation function for classification
+        return F.log_softmax(x, dim=1)
+
+
+def load_cora(path='./cora', device='cpu'):
+    """
+    The graph convolutional operation rquires normalize the adjacency matrix: D^(-1/2) * A * D^(-1/2). This step 
+    scales the adjacency matrix such that the features of neighboring nodes are weighted appropriately during 
+    aggregation. The steps involved in the renormalization trick are as follows:
+        - Compute the degree matrix.
+        - Compute the inverse square root of the degree matrix.
+        - Multiply the inverse square root of the degree matrix with the adjacency matrix.
+    """
+
+    # Set the paths to the data files
+    content_path = os.path.join(path, 'cora.content')
+    cites_path = os.path.join(path, 'cora.cites')
+
+    # Load data from files
+    content_tensor = np.genfromtxt(content_path, dtype=np.dtype(str))
+    cites_tensor = np.genfromtxt(cites_path, dtype=np.int32)
+
+    # Process features
+    features = torch.FloatTensor(content_tensor[:, 1:-1].astype(np.int32)) # Extract feature values
+    scale_vector = torch.sum(features, dim=1) # Compute sum of features for each node
+    scale_vector = 1 / scale_vector # Compute reciprocal of the sums
+    scale_vector[scale_vector == float('inf')] = 0 # Handle division by zero cases
+    scale_vector = torch.diag(scale_vector).to_sparse() # Convert the scale vector to a sparse diagonal matrix
+    features = scale_vector @ features # Scale the features using the scale vector
+
+    # Process labels
+    classes, labels = np.unique(content_tensor[:, -1], return_inverse=True) # Extract unique classes and map labels to indices
+    labels = torch.LongTensor(labels) # Convert labels to a tensor
+
+    # Process adjacency matrix
+    idx = content_tensor[:, 0].astype(np.int32) # Extract node indices
+    idx_map = {id: pos for pos, id in enumerate(idx)} # Create a dictionary to map indices to positions
+
+    # Map node indices to positions in the adjacency matrix
+    edges = np.array(
+        list(map(lambda edge: [idx_map[edge[0]], idx_map[edge[1]]], 
+            cites_tensor)), dtype=np.int32)
+
+    V = len(idx) # Number of nodes
+    E = edges.shape[0] # Number of edges
+    adj_mat = torch.sparse_coo_tensor(edges.T, torch.ones(E), (V, V), dtype=torch.int64) # Create the initial adjacency matrix as a sparse tensor
+    adj_mat = torch.eye(V) + adj_mat # Add self-loops to the adjacency matrix
+
+    degree_mat = torch.sum(adj_mat, dim=1) # Compute the sum of each row in the adjacency matrix (degree matrix)
+    degree_mat = torch.sqrt(1 / degree_mat) # Compute the reciprocal square root of the degrees
+    degree_mat[degree_mat == float('inf')] = 0 # Handle division by zero cases
+    degree_mat = torch.diag(degree_mat).to_sparse() # Convert the degree matrix to a sparse diagonal matrix
+
+    adj_mat = degree_mat @ adj_mat @ degree_mat # Apply the renormalization trick
+
+    return features.to_sparse().to(device), labels.to(device), adj_mat.to_sparse().to(device)
+
+
+def train_iter(epoch, model, optimizer, criterion, input, target, mask_train, mask_val, print_every=10):
+    start_t = time.time()
+    model.train()
+    optimizer.zero_grad()
+
+    # Forward pass
+    output = model(*input) 
+    loss = criterion(output[mask_train], target[mask_train]) # Compute the loss using the training mask
+
+    loss.backward()
+    optimizer.step()
+
+    # Evaluate the model performance on training and validation sets
+    loss_train, acc_train = test(model, criterion, input, target, mask_train)
+    loss_val, acc_val = test(model, criterion, input, target, mask_val)
+
+    if epoch % print_every == 0:
+        # Print the training progress at specified intervals
+        print(f'Epoch: {epoch:04d} ({(time.time() - start_t):.4f}s) loss_train: {loss_train:.4f} acc_train: {acc_train:.4f} loss_val: {loss_val:.4f} acc_val: {acc_val:.4f}')
+
+
+def test(model, criterion, input, target, mask):
+    model.eval()
+    with torch.no_grad():
+        output = model(*input)
+        output, target = output[mask], target[mask]
+
+        loss = criterion(output, target)
+        acc = (output.argmax(dim=1) == target).float().sum() / len(target)
+    return loss.item(), acc.item()
+
+
+if __name__ == '__main__':
+    device = 'cuda' if torch.cuda.is_available() else 'cpu'
+
+    parser = argparse.ArgumentParser(description='PyTorch Graph Convolutional Network')
+    parser.add_argument('--epochs', type=int, default=200,
+                        help='number of epochs to train (default: 200)')
+    parser.add_argument('--lr', type=float, default=0.01,
+                        help='learning rate (default: 0.01)')
+    parser.add_argument('--l2', type=float, default=5e-4,
+                        help='weight decay (default: 5e-4)')
+    parser.add_argument('--dropout-p', type=float, default=0.5,
+                        help='dropout probability (default: 0.5)')
+    parser.add_argument('--hidden-dim', type=int, default=16,
+                        help='dimension of the hidden representation (default: 16)')
+    parser.add_argument('--val-every', type=int, default=20,
+                        help='epochs to wait for print training and validation evaluation (default: 20)')
+    parser.add_argument('--include-bias', action='store_true', default=False,
+                        help='use bias term in convolutions (default: False)')
+    parser.add_argument('--no-cuda', action='store_true', default=False,
+                        help='disables CUDA training')
+    parser.add_argument('--no-mps', action='store_true', default=False,
+                        help='disables macOS GPU training')
+    parser.add_argument('--dry-run', action='store_true', default=False,
+                        help='quickly check a single pass')
+    parser.add_argument('--seed', type=int, default=42, metavar='S',
+                        help='random seed (default: 42)')
+    args = parser.parse_args()
+
+    use_cuda = not args.no_cuda and torch.cuda.is_available()
+    use_mps = not args.no_mps and torch.backends.mps.is_available()
+
+    torch.manual_seed(args.seed)
+
+    if use_cuda:
+        device = torch.device('cuda')
+    elif use_mps:
+        device = torch.device('mps')
+    else:
+        device = torch.device('cpu')
+    print(f'Using {device} device')
+
+    cora_url = 'https://linqs-data.soe.ucsc.edu/public/lbc/cora.tgz'
+    print('Downloading dataset...')
+    with requests.get(cora_url, stream=True) as tgz_file:
+        with tarfile.open(fileobj=tgz_file.raw, mode='r:gz') as tgz_object:
+            tgz_object.extractall()
+
+    print('Loading dataset...')
+    features, labels, adj_mat = load_cora(device=device)
+    idx = torch.randperm(len(labels)).to(device)
+    idx_test, idx_val, idx_train = idx[:1000], idx[1000:1500], idx[1500:]
+
+    gcn = GCN(features.shape[1], args.hidden_dim, labels.max().item() + 1,args.include_bias, args.dropout_p).to(device)
+    optimizer = Adam(gcn.parameters(), lr=args.lr, weight_decay=args.l2)
+    criterion = nn.NLLLoss()
+
+    for epoch in range(args.epochs):
+        train_iter(epoch + 1, gcn, optimizer, criterion, (features, adj_mat), labels, idx_train, idx_val, args.val_every)
+        if args.dry_run:
+            break
+
+    loss_test, acc_test = test(gcn, criterion, (features, adj_mat), labels, idx_test)
+    print(f'Test set results: loss {loss_test:.4f} accuracy {acc_test:.4f}')

Diff for: gcn/requirements.txt

@@ -0,0 +1,4 @@
+torch
+torchvision
+requests
+numpy

Diff for: run_python_examples.sh

@@ -172,6 +172,11 @@ function word_language_model() {
   python main.py --epochs 1 --dry-run $CUDA_FLAG --mps || error "word_language_model failed"
 }
 
+function gcn() {
+  start
+  python main.py --epochs 1 --dry-run || error "graph convolutional network failed"
+}
+
 function clean() {
   cd $BASE_DIR
   echo "running clean to remove cruft"
@@ -192,7 +197,8 @@ function clean() {
     super_resolution/model_epoch_1.pth \
     time_sequence_prediction/predict*.pdf \
     time_sequence_prediction/traindata.pt \
-    word_language_model/model.pt || error "couldn't clean up some files"
+    word_language_model/model.pt \
+    gcn/cora/ || error "couldn't clean up some files"
 
   git checkout fast_neural_style/images/output-images/amber-candy.jpg || error "couldn't clean up fast neural style image"
 }
@@ -217,6 +223,7 @@ function run_all() {
   vision_transformer
   word_language_model
   fx
+  gcn
 }
 
 # by default, run all examples