Added TAGConv layer (#430)

* tagconv first attempt

* tagconv first attempt

* fix

* fix

* Update src/layers/conv.jl

Co-authored-by: Carlo Lucibello <[email protected]>

---------

Co-authored-by: Carlo Lucibello <[email protected]>

Author: rbSparky

src/GraphNeuralNetworks.jl

@@ -65,6 +65,7 @@ export
       ResGatedGraphConv,
       SAGEConv,
       SGConv,
+      TAGConv,
       TransformerConv,
 
 # layers/heteroconv

src/layers/conv.jl

@@ -1590,6 +1590,132 @@ function Base.show(io::IO, l::SGConv)
     print(io, ")")
 end
 
+@doc raw"""
+    TAGConv(in => out, k=3; bias=true, init=glorot_uniform, add_self_loops=true, use_edge_weight=false)
+
+TAGConv layer from [Topology Adaptive Graph Convolutional Networks](https://arxiv.org/pdf/1710.10370.pdf).
+This layer extends the idea of graph convolutions by applying filters that adapt to the topology of the data. 
+It performs the operation:
+
+```math
+H^{K} = {\sum}_{k=0}^K (D^{-1/2} A D^{-1/2})^{k} X {\Theta}_{k}
+```
+
+where `A` is the adjacency matrix of the graph, `D` is the degree matrix, `X` is the input feature matrix, and ``{\Theta}_{k}`` is a unique weight matrix for each hop `k`.
+
+# Arguments
+- `in`: Number of input features.
+- `out`: Number of output features.
+- `k`: Maximum number of hops to consider. Default is `3`.
+- `bias`: Whether to include a learnable bias term. Default is `true`.
+- `init`: Initialization function for the weights. Default is `glorot_uniform`.
+- `add_self_loops`: Whether to add self-loops to the adjacency matrix. Default is `true`.
+- `use_edge_weight`: If `true`, edge weights are considered in the computation (if available). Default is `false`.
+
+# Examples
+
+```julia
+# Example graph data
+s = [1, 1, 2, 3]
+t = [2, 3, 1, 1]
+g = GNNGraph(s, t)  # Create a graph
+x = randn(Float32, 3, g.num_nodes)  # Random features for each node
+
+# Create a TAGConv layer
+l = TAGConv(3 => 5, k=3; add_self_loops=true)
+
+# Apply the TAGConv layer
+y = l(g, x)  # Output size: 5 × num_nodes
+```
+"""
+struct TAGConv{A <: AbstractMatrix, B} <: GNNLayer
+    weight::A
+    bias::B
+    k::Int
+    add_self_loops::Bool
+    use_edge_weight::Bool
+end
+
+
+@functor TAGConv
+
+function TAGConv(ch::Pair{Int, Int}, k = 3;
+                  init = glorot_uniform,
+                  bias::Bool = true,
+                  add_self_loops = true,
+                  use_edge_weight = false)
+    in, out = ch
+    W = init(out, in)
+    b = bias ? Flux.create_bias(W, true, out) : false
+    TAGConv(W, b, k, add_self_loops, use_edge_weight)
+end
+
+function (l::TAGConv)(g::GNNGraph, x::AbstractMatrix{T},
+                     edge_weight::EW = nothing) where
+    {T, EW <: Union{Nothing, AbstractVector}}
+    @assert !(g isa GNNGraph{<:ADJMAT_T} && edge_weight !== nothing) "Providing external edge_weight is not yet supported for adjacency matrix graphs"
+
+    if edge_weight !== nothing
+        @assert length(edge_weight)==g.num_edges "Wrong number of edge weights (expected $(g.num_edges) but given $(length(edge_weight)))"
+    end
+
+    if l.add_self_loops
+        g = add_self_loops(g)
+        if edge_weight !== nothing
+            edge_weight = [edge_weight; fill!(similar(edge_weight, g.num_nodes), 1)]
+            @assert length(edge_weight) == g.num_edges
+        end
+    end
+    Dout, Din = size(l.weight)
+    if edge_weight !== nothing
+        d = degree(g, T; dir = :in, edge_weight)
+    else
+        d = degree(g, T; dir = :in, edge_weight=l.use_edge_weight)
+    end
+    c = 1 ./ sqrt.(d)
+
+    sum_pow = 0
+    sum_total = 0
+    for iter in 1:(l.k)
+        x = x .* c'
+        if edge_weight !== nothing
+            x = propagate(e_mul_xj, g, +, xj = x, e = edge_weight)
+        elseif l.use_edge_weight
+            x = propagate(w_mul_xj, g, +, xj = x)
+        else
+            x = propagate(copy_xj, g, +, xj = x)
+        end
+        x = x .* c'
+
+        # On the first iteration, initialize sum_pow with the first propagated features
+        # On subsequent iterations, accumulate propagated features
+        if iter == 1
+            sum_pow = x
+            sum_total = l.weight * sum_pow
+        else
+            sum_pow += x            
+            # Weighted sum of features for each power of adjacency matrix
+            # This applies the weight matrix to the accumulated sum of propagated features
+            sum_total += l.weight * sum_pow
+        end
+    end
+
+    return (sum_total .+ l.bias)
+end
+
+function (l::TAGConv)(g::GNNGraph{<:ADJMAT_T}, x::AbstractMatrix,
+                     edge_weight::AbstractVector)
+    g = GNNGraph(edge_index(g)...; g.num_nodes)
+    return l(g, x, edge_weight)
+end
+
+function Base.show(io::IO, l::TAGConv)
+    out, in = size(l.weight)
+    print(io, "TAGConv($in => $out")
+    l.k == 1 || print(io, ", ", l.k)
+    print(io, ")")
+end
+
 @doc raw"""
     EGNNConv((in, ein) => out; hidden_size=2in, residual=false)
     EGNNConv(in => out; hidden_size=2in, residual=false)

test/layers/conv.jl

@@ -287,6 +287,21 @@ end
     end
 end
 
+@testset "TAGConv" begin
+    K = [1, 2, 3]
+    for k in K
+        l = TAGConv(in_channel => out_channel, k, add_self_loops = true)
+        for g in test_graphs
+            test_layer(l, g, rtol = RTOL_HIGH, outsize = (out_channel, g.num_nodes))
+        end
+
+        l = TAGConv(in_channel => out_channel, k, add_self_loops = true)
+        for g in test_graphs
+            test_layer(l, g, rtol = RTOL_HIGH, outsize = (out_channel, g.num_nodes))
+        end
+    end
+end
+
 @testset "EGNNConv" begin
     hin = 5
     hout = 5