(svn r25356) -Add: Multi-Commodity-Flow solver for link graph

src/linkgraph/mcf.h

@@ -0,0 +1,92 @@
+/** @file mcf.h Declaration of Multi-Commodity-Flow solver */
+
+#ifndef MCF_H
+#define MCF_H
+
+#include "linkgraphjob_base.h"
+#include <vector>
+
+typedef std::vector<Path *> PathVector;
+
+/**
+ * Multi-commodity flow calculating base class.
+ */
+class MultiCommodityFlow {
+protected:
+	/**
+	 * Constructor.
+	 * @param job Link graph job being executed.
+	 */
+	MultiCommodityFlow(LinkGraphJob &job) : job(job),
+			max_saturation(job.Settings().short_path_saturation)
+	{}
+
+	template<class Tannotation, class Tedge_iterator>
+	void Dijkstra(NodeID from, PathVector &paths);
+
+	uint PushFlow(Edge &edge, Path *path, uint accuracy, uint max_saturation);
+
+	void CleanupPaths(NodeID source, PathVector &paths);
+
+	LinkGraphJob &job;   ///< Job we're working with.
+	uint max_saturation; ///< Maximum saturation for edges.
+};
+
+/**
+ * First pass of the MCF calculation. Saturates shortest paths first, creates
+ * new paths if needed, eliminates cycles. This calculation is of exponential
+ * complexity in the number of nodes but the constant factors are sufficiently
+ * small to make it usable for most real-life link graph components. You can
+ * deal with performance problems that might occur here in multiple ways:
+ * - The overall accuracy is used here to determine how much flow is assigned
+ *   in each loop. The lower the accuracy, the more flow is assigned, the less
+ *   loops it takes to assign all flow.
+ * - The short_path_saturation setting determines when this pass stops. The
+ *   lower you set it, the less flow will be assigned in this pass, the less
+ *   time it will take.
+ * - You can increase the recalculation interval to allow for longer running
+ *   times without creating lags.
+ */
+class MCF1stPass : public MultiCommodityFlow {
+private:
+	bool EliminateCycles();
+	bool EliminateCycles(PathVector &path, NodeID origin_id, NodeID next_id);
+	void EliminateCycle(PathVector &path, Path *cycle_begin, uint flow);
+	uint FindCycleFlow(const PathVector &path, const Path *cycle_begin);
+public:
+	MCF1stPass(LinkGraphJob &job);
+};
+
+/**
+ * Second pass of the MCF calculation. Saturates paths with most capacity left
+ * first and doesn't create any paths along edges that haven't been visited in
+ * the first pass. This is why it doesn't have to do any cycle detection and
+ * elimination. As cycle detection is the most intense problem in the first
+ * pass this pass is cheaper. The accuracy is used here, too.
+ */
+class MCF2ndPass : public MultiCommodityFlow {
+public:
+	MCF2ndPass(LinkGraphJob &job);
+};
+
+/**
+ * Link graph handler for MCF. Creates MultiCommodityFlow instance according to
+ * the template parameter.
+ */
+template<class Tpass>
+class MCFHandler : public ComponentHandler {
+public:
+
+	/**
+	 * Run the calculation.
+	 * @param graph Component to be calculated.
+	 */
+	virtual void Run(LinkGraphJob &job) const { Tpass pass(job); }
+
+	/**
+	 * Destructor. Has to be given because of virtual Run().
+	 */
+	virtual ~MCFHandler() {}
+};
+
+#endif /* MCF_H */