GraphSAGE 到底在训练什么？ 图上的Mini-Batch 是怎么训练的 ?

1.?一个端到端的 同构图（Cora数据集）节点分类代码：

import argparse

import dgl
import dgl.nn as dglnn

import torch
import torch.nn as nn
import torch.nn.functional as F
from dgl import AddSelfLoop
from dgl.data import CiteseerGraphDataset, CoraGraphDataset, PubmedGraphDataset


class SAGE(nn.Module):
    def __init__(self, in_size, hid_size, out_size):
        super().__init__()
        self.layers = nn.ModuleList()
        # two-layer GraphSAGE-mean
        self.layers.append(dglnn.SAGEConv(in_size, hid_size, "gcn"))
        self.layers.append(dglnn.SAGEConv(hid_size, out_size, "gcn"))
        self.dropout = nn.Dropout(0.5)

    def forward(self, graph, x):
        h = self.dropout(x)
        for l, layer in enumerate(self.layers):
            h = layer(graph, h)
            if l != len(self.layers) - 1:
                h = F.relu(h)
                h = self.dropout(h)
        return h


def evaluate(g, features, labels, mask, model):
    model.eval()
    with torch.no_grad():
        logits = model(g, features)
        logits = logits[mask]
        labels = labels[mask]
        _, indices = torch.max(logits, dim=1)
        correct = torch.sum(indices == labels)
        return correct.item() * 1.0 / len(labels)


def train(g, features, labels, masks, model):
    # define train/val samples, loss function and optimizer
    train_mask, val_mask = masks
    loss_fcn = nn.CrossEntropyLoss()
    optimizer = torch.optim.Adam(model.parameters(), lr=1e-2, weight_decay=5e-4)

    # training loop
    for epoch in range(200):
        model.train()
        logits = model(g, features)
        loss = loss_fcn(logits[train_mask], labels[train_mask])
        optimizer.zero_grad()
        loss.backward()
        optimizer.step()
        acc = evaluate(g, features, labels, val_mask, model)
        print(
            "Epoch {:05d} | Loss {:.4f} | Accuracy {:.4f} ".format(
                epoch, loss.item(), acc
            )
        )


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="GraphSAGE")
    parser.add_argument(
        "--dataset",
        type=str,
        default="cora",
        help="Dataset name ('cora', 'citeseer', 'pubmed')",
    )
    parser.add_argument(
        "--dt",
        type=str,
        default="float",
        help="data type(float, bfloat16)",
    )
    args = parser.parse_args()
    print(f"Training with DGL built-in GraphSage module")

    # load and preprocess dataset
    transform = (
        AddSelfLoop()
    )  # by default, it will first remove self-loops to prevent duplication
    if args.dataset == "cora":
        data = CoraGraphDataset(transform=transform)
    elif args.dataset == "citeseer":
        data = CiteseerGraphDataset(transform=transform)
    elif args.dataset == "pubmed":
        data = PubmedGraphDataset(transform=transform)
    else:
        raise ValueError("Unknown dataset: {}".format(args.dataset))
    g = data[0]
    device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
    g = g.int().to(device)
    features = g.ndata["feat"]
    labels = g.ndata["label"]
    masks = g.ndata["train_mask"], g.ndata["val_mask"]

    # create GraphSAGE model
    in_size = features.shape[1]
    out_size = data.num_classes
    model = SAGE(in_size, 16, out_size).to(device)

    # convert model and graph to bfloat16 if needed
    if args.dt == "bfloat16":
        g = dgl.to_bfloat16(g)
        features = features.to(dtype=torch.bfloat16)
        model = model.to(dtype=torch.bfloat16)

    # model training
    print("Training...")
    train(g, features, labels, masks, model)

    # test the model
    print("Testing...")
    acc = evaluate(g, features, labels, g.ndata["test_mask"], model)
    print("Test accuracy {:.4f}".format(acc))

2.?GraphSAGE的实现 ： SAGEConv 类：

我们先来介绍一下DGL对GraphSAGE这个模型的实现：SAGEConv() 在三方库的下述位置：