GomoryHuTree.h

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/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/*                                                                           */
/*                  This file is part of the program and library             */
/*         SCIP --- Solving Constraint Integer Programs                      */
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/*    Copyright (C) 2002-2019 Konrad-Zuse-Zentrum                            */
/*                            fuer Informationstechnik Berlin                */
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/*  SCIP is distributed under the terms of the ZIB Academic License.         */
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/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/**@file   GomoryHuTree.h
 * @brief  generator for global cuts in undirected graphs
 * @author Georg Skorobohatyj
 * @author Timo Berthold
 */

/*---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0----+----1----+----2*/

#ifndef __GOMORYHUTREE_H__
#define __GOMORYHUTREE_H__

#include "objscip/objscip.h"


typedef struct GraphNode
{
   int                   id;            /**< number of the node*/
   int                   dist;   
 
   double                x;             /**< 2D-coordinate in some metric*/
   double                y;             /**< second coordinate */
   double                excess;
   double                mincap;        /**< capacity of minimum cut between node and parent in GH cut tree */

   SCIP_Bool             unmarked;      /**< while BFS in progress */
   SCIP_Bool             alive;    

   struct GraphEdge      *first_edge;   /**< in list of incident edges */
   struct GraphEdge      *scan_ptr;     /**< next edge to be scanned when node will be visited again */
  
   struct GraphNode      *bfs_link;     /**< for one way BFS working queue */
   struct GraphNode      *stack_link;   /**< for stack of active node */
   struct GraphNode      *parent;       /**< pointer of Gomory-Hu cut tree */
} GRAPHNODE;


typedef struct GraphEdge
{ 
   double                cap;           /**< capacity used in maxflow */
   double                rcap;          /**< residual capacity used in maxflow */
   double                length;        /**< length of the edge measured by some fixed metric */

   struct GraphEdge      *next;         /**< in incidence list of node from which edge is emanating */
   struct GraphEdge      *back;         /**< pointer to reverse edge */

   GRAPHNODE             *adjac;        /**< pointer to adjacent node */
   
   SCIP_VAR*             var;
} GRAPHEDGE;


typedef struct Graph
{ 
   int                   nuses;   
   int                   nnodes;        /**< number of nodes of the graph */
   int                   nedges;        /**< number of edges */
   int                   nedgesnonzero;        

   GRAPHNODE             *nodes;        /**< array containing the nodes of the graph */

   GRAPHEDGE             *edges;        /**< array containing all halfedges (thus, it's size is two times nedges) */
} GRAPH;


extern
SCIP_Bool create_graph(int n, int m, GRAPH** gr);

extern
void capture_graph(GRAPH* gr);
   
extern
void release_graph(GRAPH** gr);
   
extern
SCIP_Bool gmincut(GRAPH *gr, double *mincap, long *n_shore);

extern
SCIP_Bool ghc_tree(GRAPH *gr, SCIP_Bool** cuts, int* ncuts, double minviol);

#endif