add eccentricity

src/IGraph/Algorithms/Structure.chs

@@ -4,6 +4,8 @@ module IGraph.Algorithms.Structure
     ( -- * Shortest Path Related Functions
       shortestPath
     , diameter
+    , eccentricity
+      -- * Graph Components
     , inducedSubgraph
     , isConnected
     , isStronglyConnected
@@ -11,6 +13,8 @@ module IGraph.Algorithms.Structure
     , isDag
     , topSort
     , topSortUnsafe
+      -- * Auxiliary types
+    , Neimode(IgraphOut,IgraphIn,IgraphAll) -- not IgraphTotal
     ) where
 
 import           Control.Monad
@@ -88,6 +92,25 @@ diameter graph directed unconn = unsafePerformIO $
     , `Bool'
     } -> `CInt' void- #}
 
+-- | Eccentricity of some vertices.
+eccentricity :: Graph d v e
+             -> Neimode -- ^ 'IgraphOut' to follow edges' direction,
+                        -- 'IgraphIn' to reverse it, 'IgraphAll' to ignore
+             -> [Node]  -- ^ vertices for which to calculate eccentricity
+             -> [Double]
+eccentricity graph mode vids = unsafePerformIO $
+  allocaVector $ \res ->
+  withVerticesList vids $ \vs -> do
+    igraphEccentricity (_graph graph) res vs mode
+    toList res
+{-# INLINE igraphEccentricity #-}
+{#fun igraph_eccentricity as ^
+    { `IGraph'
+    , castPtr `Ptr Vector'
+    , castPtr %`Ptr VertexSelector'
+    , `Neimode'
+    } -> `CInt' void- #}
+
 -- | Creates a subgraph induced by the specified vertices. This function collects
 -- the specified vertices and all edges between them to a new graph.
 inducedSubgraph :: (Ord v, Serialize v)

tests/Test/Algorithms.hs

@@ -22,6 +22,7 @@ tests = testGroup "Algorithms"
     , motifTest
     , cliqueTest
     , diameterTest
+    , eccentricityTest
     , subGraphs
     , decomposeTest
     , pagerankTest
@@ -64,6 +65,16 @@ diameterTest = testGroup "Diameters"
     , testCase "ring"   $ fst (diameter (ring 10)          U False) @?= 5
     ]
 
+eccentricityTest :: TestTree
+eccentricityTest = testGroup "Eccentricity"
+    [ testCase "clique" $
+        eccentricity (full @'U 10 False) IgraphAll [0..9] @?= replicate 10 1
+    , testCase "star" $
+        eccentricity (star 10) IgraphAll [0..9] @?= (1 : replicate 9 2)
+    , testCase "ring" $
+        eccentricity (ring 10) IgraphAll [0..9] @?= replicate 10 5
+    ]
+
 subGraphs :: TestTree
 subGraphs = testGroup "generate induced subgraphs"
     [ testCase "" $ test case1 ]