X-Git-Url: https://mattmccutchen.net/match/match.git/blobdiff_plain/00f7bf547ecc8b9a709c6fbeff55b9b0d05ecffe..fd0d2377785ca843a46b0050a7351dac82c84777:/program/CS2MinCostFlow.hs

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+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