event_shadowtree.h

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/*         SCIP --- Solving Constraint Integer Programs                      */
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/**@file   event_shadowtree.c
 * @ingroup DEFPLUGINS_EVENT
 * @brief  event handler for maintaining the unmodified branch-and-bound tree
 * @author Jasper van Doornmalen
 *
 * It is possible that SCIP detects that variable bounds can be restricted globally further than formerly known.
 * In that case, it is decided to update the global bounds of these variables, and modify the history of the branching
 * decisions this way. This breaks methods that depend on the assumption that historic choices in the branch-and-bound
 * tree remain unmodified througout the search, e.g., dynamic symmetry handling constraints.
 *
 * This event handler registers decisions made by the branch-and-bound tree directly at the moment of branching, and
 * does not modify those at later stages of the solve.
 */
 
/*--+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0----+----1----+----2*/
 
#ifndef __SCIP_EVENT_SHADOWTREE_H__
#define __SCIP_EVENT_SHADOWTREE_H__
 
#include "scip/def.h"
#include "scip/type_scip.h"
#include "scip/type_event.h"
#include "scip/type_tree.h"
#include "scip/type_var.h"
#include "scip/type_misc.h"
 
#ifdef __cplusplus
extern "C" {
#endif
 
/** bound change for branch-and-bound tree node in shadow tree */
struct SCIP_ShadowBoundUpdate
{
   SCIP_VAR*             var;                /**< changed variable */
   SCIP_Real             newbound;           /**< bound change */
   SCIP_BOUNDTYPE        boundchgtype;       /**< which bound of variable is changed (upper or lower) */
};
typedef struct SCIP_ShadowBoundUpdate SCIP_SHADOWBOUNDUPDATE;
 
/** branch-and-bound tree node for the shadowtree */
struct SCIP_ShadowNode
{
   SCIP_Longint          nodeid;             /**< ID of corresponding branch-and-bound tree node */
   struct SCIP_ShadowNode* parent;           /**< parent of this shadowtree node. NULL iff it is the root node */
   struct SCIP_ShadowNode** children;        /**< list of children of this shadowtree node. NULL iff it is a leaf */
   int                   nchildren;          /**< number of elements in children
                                              *   0 iff it is a leaf, -1 iff original node is DELETED */
   SCIP_SHADOWBOUNDUPDATE* branchingdecisions;/**< the variables branched on in this node.
                                               *  NULL iff nbranchingdecisions == 0 */
   int                   nbranchingdecisions;/**< the number of variables branched on in this node
                                              *   0 iff branchingdecisions == NULL */
   SCIP_SHADOWBOUNDUPDATE* propagations;     /**< the propagation (and branching decisions) updates in the node
                                              *   This is populated after branching with the propagations in that node.
                                              *   NULL iff npropagations == 0 */
   int                   npropagations;      /**< the number of propagations. 0 iff propagations == NULL */
};
typedef struct SCIP_ShadowNode SCIP_SHADOWNODE;
 
/** shadow tree data structure */
struct SCIP_ShadowTree
{
   SCIP_HASHTABLE*       nodemap;            /**< pointer to the hashmap containing all shadow tree nodes */
};
typedef struct SCIP_ShadowTree SCIP_SHADOWTREE;
 
/** get the time spent in the shadow tree eventhdlr */
SCIP_EXPORT
SCIP_Real SCIPgetShadowTreeEventHandlerExecutionTime(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_EVENTHDLR*       eventhdlr           /**< event handler */
);
 
/** given a node number, returns the node in the shadow tree, or NULL if it doesn't exist */
SCIP_EXPORT
SCIP_SHADOWNODE* SCIPshadowTreeGetShadowNodeFromNodeNumber(
   SCIP_SHADOWTREE*      shadowtree,         /**< pointer to the shadow tree */
   SCIP_Longint          nodeno              /**< index of the node, equivalent to the standard branch-and-bound tree */
);
 
/** given a node, returns the node in the shadowtree, or NULL if it doesn't exist */
SCIP_EXPORT
SCIP_SHADOWNODE* SCIPshadowTreeGetShadowNode(
   SCIP_SHADOWTREE*      shadowtree,         /**< pointer to the shadow tree */
   SCIP_NODE*            node                /**< node from the actual branch-and-bound tree */
);
 
/** gets the shadow tree */
SCIP_EXPORT
SCIP_SHADOWTREE* SCIPgetShadowTree(
   SCIP_EVENTHDLR*       eventhdlr           /**< event handler */
);
 
/** activates shadow tree eventhandler if it is not already activated (which keeps a copy of the tree) */
SCIP_EXPORT
SCIP_RETCODE SCIPactivateShadowTree(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_EVENTHDLR*       eventhdlr           /**< event handler */
);
 
/** creates event handler for event */
SCIP_EXPORT
SCIP_RETCODE SCIPincludeEventHdlrShadowTree(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_EVENTHDLR**      eventhdlrptr        /**< pointer to store the event handler */
);
 
#ifdef __cplusplus
}
#endif
 
#endif