+module CS2MinCostFlow (minCostFlow) where
+import IMinCostFlow
+import IOStuff
+import System.IO.Unsafe
+import Data.Graph.Inductive.Graph
+import Data.Array.IArray
+import Data.List
+import Data.Function
+
+-- Configure the path to cs2.exe relative to the program/ directory here.
+cs2cmd = "./cs2.exe"
+
+runCS2 :: String -> String
+-- Using unsafePerformIO is non-ideal, but it gives a consistent interface
+-- for the min-cost flow function.
+runCS2 inData = unsafePerformIO (interactWithCommand cs2cmd inData)
+
+data MCFEdge i f c = MCFEdge {
+ eFrom :: Node,
+ eTo :: Node,
+ eCost :: c,
+ eMIdx :: Maybe i,
+ eCap :: f
+} deriving (Eq, Ord)
+
+round2 :: Real a => a -> Int
+round2 x = fromInteger (round (toRational x))
+
+minCostFlow :: MinCostFlowImpl
+minCostFlow idxBounds edgeIdx edgeCap edgeCost theGraph (source, sink) =
+ let
+ (nLo, nHi) = nodeRange theGraph
+ theEdges = labEdges theGraph
+ -- HACK: Add a highly negative-cost edge from sink to
+ -- source to get CS2 to compute a max flow.
+ edges2 = MCFEdge sink source (-100000) Nothing 10000 :
+ map (\(n1, n2, l) -> MCFEdge n1 n2 (edgeCost l) (Just (edgeIdx l)) (edgeCap l))
+ theEdges
+ -- HACK: Round capacities and costs to integers so CS2 can
+ -- handle them. The proposal matcher's capacities are integers,
+ -- and its costs are so large that the error should be insignificant.
+ inData = "p min " ++ show (nHi + 1 - nLo) ++ " " ++ show (length edges2) ++ "\n"
+ ++ "n 1 0\n" -- Dummy node description to make CS2 parser happy.
+ ++ concatMap (\(MCFEdge n1 n2 cost _ cap) ->
+ "a " ++ show (n1 - nLo + 1) ++ " " ++ show (n2 - nLo + 1)
+ ++ " 0 " ++ show (round2 cap)
+ ++ " " ++ show (round2 cost) ++ "\n")
+ edges2
+ outData = runCS2 inData
+ -- Unfortunately CS2 doesn't support edge ID numbers, so we
+ -- have to manually apply the "flow items" it produced to the
+ -- appropriate edges in order of increasing cost.
+ -- Extract ((n1, n2), f) tuples from the output.
+ flowItems = concatMap (\l -> let w:ws = words l in
+ if w == "f"
+ then let
+ [n1s, n2s, fs] = ws
+ n1 = (read n1s :: Int) - 1 + nLo
+ n2 = (read n2s :: Int) - 1 + nLo
+ fv = fromInteger (toInteger (read fs :: Int))
+ in [((n1, n2), fv)]
+ else []
+ ) (lines outData)
+ -- Total the flow for each node pair (n1, n2) to simplify matters.
+ flowGroups = groupBy ((==) `on` fst) (sort flowItems)
+ npFlows = map (\l@((n12, _):_) ->
+ (n12, sum $ map snd l)) flowGroups
+ applyFlows fis [] = case fis of
+ [] -> []
+ _ -> error "CS2MinCostFlow: some flow items could not be applied"
+ applyFlows fis es@(e@(MCFEdge n1 n2 _ mi cap):moreEs) =
+ let (ef, fisLeft) = case fis of
+ -- Note to self: One can't test equality in a
+ -- pattern by reusing a variable name. Use a
+ -- guard instead.
+ ((fn1, fn2), fv):moreFis | fn1 == n1 && fn2 == n2 ->
+ -- This edge gets (min f cap) flow.
+ (min fv cap, if fv > cap
+ then ((n1, n2), fv - cap) : moreFis
+ else moreFis)
+ _ -> (0, fis) -- No flow for this edge.
+ in (mi, ef) : applyFlows fisLeft moreEs
+ theEdgeFlows = applyFlows npFlows (sort edges2)
+ -- Get rid of the flow on our hack edge.
+ realEdgeFlows = concatMap (\(mi, ef) -> case mi of
+ Just i -> [(i, ef)]
+ Nothing -> []
+ ) theEdgeFlows
+ in array idxBounds realEdgeFlows