wehub-resource-sync
161 lines
6.1 KiB
Python
161 lines
6.1 KiB
Python
"""Torch Module for Attention-based Graph Neural Network layer"""
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# pylint: disable= no-member, arguments-differ, invalid-name
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import torch as th
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from torch import nn
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from torch.nn import functional as F
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from .... import function as fn
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from ....base import DGLError
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from ....utils import expand_as_pair
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from ...functional import edge_softmax
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class AGNNConv(nn.Module):
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r"""Attention-based Graph Neural Network layer from `Attention-based Graph Neural Network for
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Semi-Supervised Learning <https://arxiv.org/abs/1803.03735>`__
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.. math::
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H^{l+1} = P H^{l}
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where :math:`P` is computed as:
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.. math::
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P_{ij} = \mathrm{softmax}_i ( \beta \cdot \cos(h_i^l, h_j^l))
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where :math:`\beta` is a single scalar parameter.
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Parameters
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----------
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init_beta : float, optional
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The :math:`\beta` in the formula, a single scalar parameter.
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learn_beta : bool, optional
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If True, :math:`\beta` will be learnable parameter.
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allow_zero_in_degree : bool, optional
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If there are 0-in-degree nodes in the graph, output for those nodes will be invalid
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since no message will be passed to those nodes. This is harmful for some applications
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causing silent performance regression. This module will raise a DGLError if it detects
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0-in-degree nodes in input graph. By setting ``True``, it will suppress the check
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and let the users handle it by themselves. Default: ``False``.
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Note
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----
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Zero in-degree nodes will lead to invalid output value. This is because no message
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will be passed to those nodes, the aggregation function will be appied on empty input.
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A common practice to avoid this is to add a self-loop for each node in the graph if
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it is homogeneous, which can be achieved by:
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>>> g = ... # a DGLGraph
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>>> g = dgl.add_self_loop(g)
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Calling ``add_self_loop`` will not work for some graphs, for example, heterogeneous graph
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since the edge type can not be decided for self_loop edges. Set ``allow_zero_in_degree``
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to ``True`` for those cases to unblock the code and handle zero-in-degree nodes manually.
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A common practise to handle this is to filter out the nodes with zero-in-degree when use
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after conv.
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Example
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-------
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>>> import dgl
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>>> import numpy as np
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>>> import torch as th
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>>> from dgl.nn import AGNNConv
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>>>
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>>> g = dgl.graph(([0,1,2,3,2,5], [1,2,3,4,0,3]))
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>>> g = dgl.add_self_loop(g)
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>>> feat = th.ones(6, 10)
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>>> conv = AGNNConv()
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>>> res = conv(g, feat)
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>>> res
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tensor([[1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
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[1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
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[1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
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[1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
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[1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
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[1., 1., 1., 1., 1., 1., 1., 1., 1., 1.]],
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grad_fn=<BinaryReduceBackward>)
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"""
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def __init__(
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self, init_beta=1.0, learn_beta=True, allow_zero_in_degree=False
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):
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super(AGNNConv, self).__init__()
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self._allow_zero_in_degree = allow_zero_in_degree
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if learn_beta:
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self.beta = nn.Parameter(th.Tensor([init_beta]))
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else:
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self.register_buffer("beta", th.Tensor([init_beta]))
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def set_allow_zero_in_degree(self, set_value):
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r"""
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Description
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-----------
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Set allow_zero_in_degree flag.
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Parameters
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----------
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set_value : bool
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The value to be set to the flag.
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"""
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self._allow_zero_in_degree = set_value
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def forward(self, graph, feat):
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r"""
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Description
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-----------
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Compute AGNN layer.
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Parameters
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----------
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graph : DGLGraph
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The graph.
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feat : torch.Tensor
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The input feature of shape :math:`(N, *)` :math:`N` is the
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number of nodes, and :math:`*` could be of any shape.
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If a pair of torch.Tensor is given, the pair must contain two tensors of shape
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:math:`(N_{in}, *)` and :math:`(N_{out}, *)`, the :math:`*` in the later
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tensor must equal the previous one.
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Returns
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-------
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torch.Tensor
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The output feature of shape :math:`(N, *)` where :math:`*`
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should be the same as input shape.
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Raises
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------
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DGLError
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If there are 0-in-degree nodes in the input graph, it will raise DGLError
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since no message will be passed to those nodes. This will cause invalid output.
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The error can be ignored by setting ``allow_zero_in_degree`` parameter to ``True``.
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"""
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with graph.local_scope():
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if not self._allow_zero_in_degree:
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if (graph.in_degrees() == 0).any():
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raise DGLError(
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"There are 0-in-degree nodes in the graph, "
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"output for those nodes will be invalid. "
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"This is harmful for some applications, "
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"causing silent performance regression. "
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"Adding self-loop on the input graph by "
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"calling `g = dgl.add_self_loop(g)` will resolve "
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"the issue. Setting ``allow_zero_in_degree`` "
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"to be `True` when constructing this module will "
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"suppress the check and let the code run."
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)
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feat_src, feat_dst = expand_as_pair(feat, graph)
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graph.srcdata["h"] = feat_src
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graph.srcdata["norm_h"] = F.normalize(feat_src, p=2, dim=-1)
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if isinstance(feat, tuple) or graph.is_block:
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graph.dstdata["norm_h"] = F.normalize(feat_dst, p=2, dim=-1)
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# compute cosine distance
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graph.apply_edges(fn.u_dot_v("norm_h", "norm_h", "cos"))
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cos = graph.edata.pop("cos")
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e = self.beta * cos
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graph.edata["p"] = edge_softmax(graph, e)
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graph.update_all(fn.u_mul_e("h", "p", "m"), fn.sum("m", "h"))
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return graph.dstdata.pop("h")
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