global_mean_pool(x, batch, size:Union[int, NoneType]=None)
Returns batch-wise graph-level-outputs by averaging node features
across the node dimension, so that for a single graph
通过对节点维度上的节点特征求平均值，返回批处理图形级别的输出，从而形成一个图形
G i mathcal{G}_i G
