Docs GCNConv

Author: aurorarossi

GNNLux/src/layers/conv.jl

@@ -5,7 +5,80 @@ _getstate(s::StatefulLuxLayer{Static.True}) = s.st
 _getstate(s::StatefulLuxLayer{false}) = s.st_any
 _getstate(s::StatefulLuxLayer{Static.False}) = s.st_any
 
-
+@doc raw"""
+    GCNConv(in => out, σ=identity; [init_weight, init_bias, use_bias, add_self_loops, use_edge_weight])
+
+Graph convolutional layer from paper [Semi-supervised Classification with Graph Convolutional Networks](https://arxiv.org/abs/1609.02907).
+
+Performs the operation
+```math
+\mathbf{x}'_i = \sum_{j\in N(i)} a_{ij} W \mathbf{x}_j
+```
+where ``a_{ij} = 1 / \sqrt{|N(i)||N(j)|}`` is a normalization factor computed from the node degrees. 
+
+If the input graph has weighted edges and `use_edge_weight=true`, than ``a_{ij}`` will be computed as
+```math
+a_{ij} = \frac{e_{j\to i}}{\sqrt{\sum_{j \in N(i)}  e_{j\to i}} \sqrt{\sum_{i \in N(j)}  e_{i\to j}}}
+```
+
+# Arguments
+
+- `in`: Number of input features.
+- `out`: Number of output features.
+- `σ`: Activation function. Default `identity`.
+- `init_weight`: Weights' initializer. Default `glorot_uniform`.
+- `init_bias`: Bias initializer. Default `zeros32`.
+- `use_bias`: Add learnable bias. Default `true`.
+- `add_self_loops`: Add self loops to the graph before performing the convolution. Default `false`.
+- `use_edge_weight`: If `true`, consider the edge weights in the input graph (if available).
+                     If `add_self_loops=true` the new weights will be set to 1. 
+                     This option is ignored if the `edge_weight` is explicitly provided in the forward pass.
+                     Default `false`.
+
+# Forward
+
+    (::GCNConv)(g, x, [edge_weight], ps, st; norm_fn = d -> 1 ./ sqrt.(d), conv_weight=nothing)
+
+Takes as input a graph `g`, a node feature matrix `x` of size `[in, num_nodes]`, optionally an edge weight vector and the parameter and state of the layer. Returns a node feature matrix of size 
+`[out, num_nodes]`.
+
+The `norm_fn` parameter allows for custom normalization of the graph convolution operation by passing a function as argument. 
+By default, it computes ``\frac{1}{\sqrt{d}}`` i.e the inverse square root of the degree (`d`) of each node in the graph. 
+If `conv_weight` is an `AbstractMatrix` of size `[out, in]`, then the convolution is performed using that weight matrix.
+
+# Examples
+
+```julia
+using GNNLux, Lux, Random
+# initialize random number generator
+rng = Random.default_rng()
+Random.seed!(rng, 0)
+# create data
+s = [1,1,2,3]
+t = [2,3,1,1]
+g = GNNGraph(s, t)
+x = randn(Float32, 3, g.num_nodes)
+
+# create layer
+l = GCNConv(3 => 5) 
+
+# setup layer
+ps, st = LuxCore.setup(rng, l)
+
+# forward pass
+y = l(g, x, ps, st)       # size of the output first entry:  5 × num_nodes
+
+# convolution with edge weights and custom normalization function
+w = [1.1, 0.1, 2.3, 0.5]
+custom_norm_fn(d) = 1 ./ sqrt.(d + 1)  # Custom normalization function
+y = l(g, x, w, ps, st; norm_fn = custom_norm_fn)
+
+# Edge weights can also be embedded in the graph.
+g = GNNGraph(s, t, w)
+l = GCNConv(3 => 5, use_edge_weight=true) 
+y = l(g, x, ps, st) # same as l(g, x, w) 
+```
+"""
 @concrete struct GCNConv <: GNNLayer
     in_dims::Int
     out_dims::Int
@@ -18,7 +91,7 @@ _getstate(s::StatefulLuxLayer{Static.False}) = s.st_any
 end
 
 function GCNConv(ch::Pair{Int, Int}, σ = identity;
-                 init_weight = glorot_uniform,
+                init_weight = glorot_uniform,
                 init_bias = zeros32,
                 use_bias::Bool = true,
                 add_self_loops::Bool = true,
@@ -55,7 +128,7 @@ end
 
 function (l::GCNConv)(g, x, edge_weight, ps, st; 
             norm_fn = d -> 1 ./ sqrt.(d),
-            conv_weight=nothing, )
+            conv_weight=nothing)
 
     m = (; ps.weight, bias = _getbias(ps), 
            l.add_self_loops, l.use_edge_weight, l.σ)