[FLouvain] TotWeightSum bug fix

Should have computed only links incident to C, not the ones inside C.

src/Data/Graph/Clustering/FLouvain.hs

@@ -36,6 +36,7 @@ doi:10.1088/1742-5468/2008/10/P10008.
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE InstanceSigs      #-}
 {-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE ScopedTypeVariables #-}
 
 module Data.Graph.Clustering.FLouvain
   where
@@ -138,9 +139,11 @@ newtype NodeComWeightSum = NodeComWeightSum { unNodeComWeightSum :: Double }
 newtype GraphWeightSum = GraphWeightSum { unGraphWeightSum :: Double }
   deriving (Show, Eq, Ord)
 -- | This is the \Sum_in in formula (2) of the Louvain paper
+-- (sum of the weights of the links inside C)
 newtype InWeightSum = InWeightSum { unInWeightSum :: Double }
   deriving (Show, Eq, Ord)
 -- | This is the \Sum_tot in formula (2) of the Louvain paper
+-- (sum of the weights of the links incident to nodes in C)
 newtype TotWeightSum = TotWeightSum { unTotWeightSum :: Double }
   deriving (Show, Eq, Ord)
 -- | Computed Delta_Q value in (2)
@@ -279,7 +282,7 @@ step gw ctx@(p, v, l, s) cgr = newCgr
 
     -- k_i variable in formula (2)
     ki :: NodeWeightSum
-    ki = NodeWeightSum $ sum $ map (fedgeWeight . fst) $ p <> s
+    ki = NodeWeightSum $ sumEdgeWeights $ p <> s
 
     deltas :: [(LNode Community, DeltaQ)]
     deltas = map (\c -> (c, delta' c)) ncs
@@ -302,7 +305,7 @@ step gw ctx@(p, v, l, s) cgr = newCgr
 
 nodeComWeightSum :: Community -> Context a (FEdge b) -> NodeComWeightSum
 nodeComWeightSum com (_, _, _, s) =
-  NodeComWeightSum $ sum $ map (fedgeWeight . fst) $ filter (\(_, n) -> n `elem` comNodes com) s
+  NodeComWeightSum $ sumEdgeWeights $ filter (\(_, n) -> n `elem` comNodes com) s
 
 -- COMMUNITY GRAPH FUNCTIONS
 
@@ -339,41 +342,35 @@ moveNode gr n direction c = moveNodeWithNeighbours lnNeighbors n direction c
     lnNeighbors = lneighbors gr n
 
 -- | Same as 'moveNode' above but with only node neighbours, not whole graph
-moveNodeWithNeighbours :: Adj (FEdge b) -> Node -> Direction -> Community -> Community
+moveNodeWithNeighbours :: forall b. Adj (FEdge b) -> Node -> Direction -> Community -> Community
 moveNodeWithNeighbours lnNeighbors n direction (Community (ns, inwsum, totwsum)) =
-  Community (newNs, newInWsum, newTotWsum)
+  Community (newNs, InWeightSum newInWsum, TotWeightSum newTotWsum)
     where
-
       newNs = case direction of
         Into  -> n:ns
         OutOf -> DL.delete n ns
 
-      (newInWsum, newTotWsum) = computeWeights direction (inwsum, totwsum) sumN sumNonCom
+      (newInWsum, newTotWsum) =
+        case direction of
+          Into  -> (unInWeightSum inwsum + sumN, unTotWeightSum totwsum - sumNonCom)
+          OutOf -> (unInWeightSum inwsum - sumN, unTotWeightSum totwsum + sumNonCom)
 
       -- Update InWeightSum with connections between node and the community
       sumN :: Double
-      sumN = sum $ map (fedgeWeight . fst) comNeighbors
+      sumN = sumEdgeWeights comNeighbors
 
       -- Update TotWeightSum, subtracting connections between node and community
       -- and adding connections of node to non-community
       sumNonCom :: Double
-      sumNonCom = sum $ map (fedgeWeight . fst) nonComNeighbors
+      sumNonCom = sumEdgeWeights nonComNeighbors
 
       -- Node Adj Context
-      --comNeighbors    :: Adj (FEdge b)
+      comNeighbors    :: Adj (FEdge b)
       comNeighbors    = filter (\ln -> snd ln `elem`    ns) lnNeighbors
 
-      --nonComNeighbors :: Adj (FEdge b)
+      nonComNeighbors :: Adj (FEdge b)
       nonComNeighbors = filter (\ln -> snd ln `notElem` ns) lnNeighbors
 
--- | Recomputes 'InWeightSum' when node is moved in the 'Direciton' of
--- 'Community'. Given parameters are:
-computeWeights :: Direction -> (InWeightSum, TotWeightSum) -> Double -> Double -> (InWeightSum, TotWeightSum)
-computeWeights Into (InWeightSum inwsum, TotWeightSum totwsum) sumN sumNonCom =
-  (InWeightSum $ inwsum  + sumN, TotWeightSum $ totwsum + sumN - sumNonCom)
-computeWeights OutOf (InWeightSum inwsum, TotWeightSum totwsum) sumN sumNonCom =
-  (InWeightSum $ inwsum  - sumN, TotWeightSum $ totwsum - sumN + sumNonCom)
-
 
 {-
 -- | Moves 'Node' between two 'Community'ies, recomputing their weights