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Fix bug in modularity calculation

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Summary:
This diff does not fix our Louvain implementation completely. The algorithm
internally still optimzies the wrong function, but this will at least correctly
calculate the modularity value at the end.

Fix of the algorithm will come in a separate diff

Reviewers: dsantl

Reviewed By: dsantl

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D2603
This commit is contained in:
Ivan Paljak 2019-12-16 15:22:53 +01:00
parent 0c111d52dc
commit ec67e71d39
2 changed files with 51 additions and 5 deletions
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11
query_modules/louvain/src/data_structures/graph.cpp
View File

@ -78,14 +78,23 @@ double Graph::Modularity() const {
if (total_w_ == 0)
return 0;
std::unordered_map<uint32_t, double> weight_c;
std::unordered_map<uint32_t, double> degree_c;
for (uint32_t i = 0; i < n_nodes_; ++i) {
degree_c[Community(i)] +=
static_cast<double>(IncidentWeight(i));
for (const auto &neigh : adj_list_[i]) {
uint32_t j = neigh.dest;
double w = neigh.weight;
if (Community(i) != Community(j)) continue;
ret += w - (IncidentWeight(i) * IncidentWeight(j) / (2.0 * total_w_));
weight_c[Community(i)] += w;
}
}
for (const auto &p : degree_c)
ret += weight_c[p.first] - (p.second * p.second) / (2 * total_w_);
ret /= 2 * total_w_;
return ret;
}

45
query_modules/louvain/test/unit/graph.cpp
View File

@ -273,7 +273,7 @@ TEST(Graph, Modularity) {
{3, 4, 4.2}});
std::vector<uint32_t> c = {0, 1, 1, 2, 2};
SetCommunities(&graph, c);
EXPECT_NEAR(graph.Modularity(), 0.37452886332076973, 1e-6);
EXPECT_NEAR(graph.Modularity(), 0.036798254314620096, 1e-6);
// Tree
// (0)--(3)
@ -289,7 +289,7 @@ TEST(Graph, Modularity) {
{2, 6, 0.7}});
c = {0, 0, 1, 0, 0, 1, 2};
SetCommunities(&graph, c);
EXPECT_NEAR(graph.Modularity(), 0.6945087219651122, 1e-6);
EXPECT_NEAR(graph.Modularity(), 0.4424617301530794, 1e-6);
// Graph without self-loops
// (0)--(1)
@ -305,7 +305,7 @@ TEST(Graph, Modularity) {
{3, 4, 0.7}});
c = {0, 1, 1, 1, 1};
SetCommunities(&graph, c);
EXPECT_NEAR(graph.Modularity(), 0.32653061224489793, 1e-6);
EXPECT_NEAR(graph.Modularity(), -0.022959183673469507, 1e-6);
// Graph with self loop [*nodes have self loops]
// (0)--(1*)
@ -324,5 +324,42 @@ TEST(Graph, Modularity) {
{4, 4, 1}});
c = {0, 0, 0, 0, 1};
SetCommunities(&graph, c);
EXPECT_NEAR(graph.Modularity(), 0.2754545454545455, 1e-6);
EXPECT_NEAR(graph.Modularity(), 0.188842975206611, 1e-6);
// Neo4j example graph
// (0)--(1)---(3)--(4)
// \ / \ /
// (2) (5)
graph = BuildGraph(6, {{0, 1, 1},
{1, 2, 1},
{0, 2, 1},
{1, 3, 1},
{3, 5, 1},
{5, 4, 1},
{3, 4, 1}});
c = {0, 0, 0, 1, 1, 1};
SetCommunities(&graph, c);
EXPECT_NEAR(graph.Modularity(), 0.3571428571428571, 1e-6);
// Example graph from wikipedia
// (0)--(1)--(3)--(4)--(5)
// \ / | \ /
// (2) (7) (6)
// / \
// (8)--(9)
graph = BuildGraph(10, {{0, 1, 1},
{1, 2, 1},
{0, 2, 1},
{1, 3, 1},
{3, 4, 1},
{4, 5, 1},
{5, 6, 1},
{6, 4, 1},
{3, 7, 1},
{7, 8, 1},
{7, 9, 1},
{8, 9, 1}});
c = {0, 0, 0, 0, 1, 1, 1, 2, 2, 2};
SetCommunities(&graph, c);
EXPECT_NEAR(graph.Modularity(), 0.4896, 1e-4);
}