cartesian_product override (#40)

* add override for cartesian_product

* add import of cartesian_product for new override

* add missing comma

* add tests for cartesian_product

Author: bubblingoak

src/SimpleWeightedGraphs.jl

@@ -15,7 +15,7 @@ import LightGraphs:
     has_vertex, has_edge, inneighbors, outneighbors,
     indegree, outdegree, degree, has_self_loops, num_self_loops,
 
-    add_vertices!, adjacency_matrix, weights, connected_components,
+    add_vertices!, adjacency_matrix, weights, connected_components, cartesian_product,
 
     AbstractGraphFormat, loadgraph, loadgraphs, savegraph,
     pagerank, induced_subgraph

src/overrides.jl

@@ -59,6 +59,26 @@ savegraph(fn::AbstractString, g::AbstractSimpleWeightedGraph, gname::AbstractStr
 savegraph(fn::AbstractString, d::Dict{T, U}; compress=true) where T <: AbstractString where U <: AbstractSimpleWeightedGraph =
     savegraph(fn, d, SWGFormat(), compress=compress)
 
+# It is possible that this is suboptimal, but it is the most trivial extension of the implementation used in LightGraphs
+function cartesian_product(g::G, h::G) where G <: AbstractSimpleWeightedGraph
+    z = G(nv(g) * nv(h))
+    id(i, j) = (i - 1) * nv(h) + j
+    for e in edges(g)
+        i1, i2 = Tuple(e)
+        for j = 1:nv(h)
+            add_edge!(z, id(i1, j), id(i2, j), weight(e))
+        end
+    end
+
+    for e in edges(h)
+        j1, j2 = Tuple(e)
+        for i in vertices(g)
+            add_edge!(z, id(i, j1), id(i, j2), weight(e))
+        end
+    end
+    return z
+end
+
 # Connected Components on a Sparse Matrix
 
 function _cc(g::SimpleWeightedGraph{T,U}) where T where U

test/overrides.jl

@@ -13,6 +13,12 @@
         gi = gx[2:4]
         @test weights(gi)[1, 2] == 99
 
+        h = @inferred(cartesian_product(g, g))
+        @test nv(h) == 25
+        @test ne(h) == 40
+        gz = g3[1:4]
+        add_edge!(gz, 3, 4, 87)
+        @test weights(cartesian_product(g3,gz))[11,12]==weights(gz)[3,4]  
     end
 
     add_edge!(g5, 1, 2, 2); add_edge!(g5, 2, 3, 2); add_edge!(g5, 1, 3, 1); add_edge!(g5, 3, 4, 5)