dgl.sum_edges¶

dgl.sum_edges(graph, feat, weight=None)[source]¶

Sums all the values of edge field feat in graph, optionally multiplies the field by a scalar edge field weight.

Parameters:	graph (DGLGraph) – The graph. feat (str) – The feature field. weight (str, optional) – The weight field. If None, no weighting will be performed, otherwise, weight each edge feature with field `feat`. for summation. The weight feature associated in the `graph` should be a tensor of shape `[graph.number_of_edges(), 1]`.
Returns:	The summed tensor.
Return type:	tensor

Notes

If graph is a BatchedDGLGraph object, a stacked tensor is returned instead, i.e. having an extra first dimension. Each row of the stacked tensor contains the readout result of the corresponding example in the batch. If an example has no edges, a zero tensor with the same shape is returned at the corresponding row.

Examples

>>> import dgl
>>> import torch as th

Create two DGLGraph objects and initialize their edge features.

>>> g1 = dgl.DGLGraph()                           # Graph 1
>>> g1.add_nodes(2)
>>> g1.add_edges([0, 1], [1, 0])
>>> g1.edata['h'] = th.tensor([[1.], [2.]])
>>> g1.edata['w'] = th.tensor([[3.], [6.]])

>>> g2 = dgl.DGLGraph()                           # Graph 2
>>> g2.add_nodes(3)
>>> g2.add_edges([0, 1, 2], [1, 2, 0])
>>> g2.edata['h'] = th.tensor([[1.], [2.], [3.]])

Sum over edge attribute h without weighting for each graph in a batched graph.

>>> bg = dgl.batch([g1, g2], edge_attrs='h')
>>> dgl.sum_edges(bg, 'h')
tensor([[3.],   # 1 + 2
        [6.]])  # 1 + 2 + 3

Sum edge attribute h with weight from edge attribute w for a single graph.

>>> dgl.sum_edges(g1, 'h', 'w')
tensor([15.])   # 1 * 3 + 2 * 6