Merge pull request #37 from Yelrose/master

Add Graph Normalization Layers

pgl/layers/graph_pool.py

@@ -19,7 +19,7 @@ from pgl import graph_wrapper
 from pgl.utils import paddle_helper
 from pgl.utils import op
 
-__all__ = ['graph_pooling']
+__all__ = ['graph_pooling', 'graph_norm']
 
 
 def graph_pooling(gw, node_feat, pool_type):
@@ -40,3 +40,28 @@ def graph_pooling(gw, node_feat, pool_type):
     graph_feat = op.nested_lod_reset(node_feat, gw.graph_lod)
     graph_feat = fluid.layers.sequence_pool(graph_feat, pool_type)
     return graph_feat
+
+
+def graph_norm(gw, feature):
+    """Implementation of graph normalization
+   
+    Reference Paper: BENCHMARKING GRAPH NEURAL NETWORKS
+   
+    Each node features is divied by sqrt(num_nodes) per graphs.
+
+    Args:
+        gw: Graph wrapper object (:code:`StaticGraphWrapper` or :code:`GraphWrapper`)
+
+        feature: A tensor with shape (num_nodes, hidden_size)
+
+    Return:
+        A tensor with shape (num_nodes, hidden_size)
+    """
+    nodes = fluid.layers.fill_constant(
+        [gw.num_nodes, 1], dtype="float32", value=1.0)
+    norm = graph_pooling(gw, nodes, pool_type="sum")
+    norm = fluid.layers.sqrt(norm)
+    feature_lod = op.nested_lod_reset(feature, gw.graph_lod)
+    norm = fluid.layers.sequence_expand_as(norm, feature_lod)
+    norm.stop_gradient = True
+    return feature_lod / norm