# SCIP

Solving Constraint Integer Programs

presol_dualagg.h
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1 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
2 /* */
3 /* This file is part of the program and library */
4 /* SCIP --- Solving Constraint Integer Programs */
5 /* */
6 /* Copyright (C) 2002-2021 Konrad-Zuse-Zentrum */
7 /* fuer Informationstechnik Berlin */
8 /* */
9 /* SCIP is distributed under the terms of the ZIB Academic License. */
10 /* */
11 /* You should have received a copy of the ZIB Academic License */
12 /* along with SCIP; see the file COPYING. If not visit scipopt.org. */
13 /* */
14 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
15
16 /**@file presol_dualagg.h
17  * @ingroup PRESOLVERS
18  * @brief aggregate variables by dual arguments
19  * @author Dieter Weninger
20  *
21  * This presolver looks for variables which could not be handled by
22  * duality fixing because of one up-/downlock.
23  * If the constraint which delivers the up-/downlock has
24  * a specific structure, we can aggregate the corresponding variable.
25  *
26  * In more detail (for a minimization problem and the case of only one uplock):
27  *
28  * Given a variable \f$x_i\f$ with \f$c_i \leq 0\f$ and only one up lock (originating from a constraint c),
29  * we are looking for a binary variable \f$x_j\f$ such that:
30  * 1. if \f$x_j = 0\f$, constraint c can only be fulfilled for \f$x_i = lb_i\f$, and
31  * 2. if \f$x_j = 1\f$, constraint c becomes redundant and \f$x_i\f$ can be dual-fixed to its upper bound \f$ub_i\f$
32  * (or vice versa). Then we can perform the following aggregation: \f$x_i = lb_i + x_j (ub_i - lb_i)\f$.
33  *
34  * Similar arguments apply for the case of only one down lock and \f$c_i \geq 0\f$.
35  */
36
37 /*---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0----+----1----+----2*/
38
39 #ifndef __SCIP_PRESOL_DUALAGG_H__
40 #define __SCIP_PRESOL_DUALAGG_H__
41
42 #include "scip/def.h"
43 #include "scip/type_retcode.h"
44 #include "scip/type_scip.h"
45
46 #ifdef __cplusplus
47 extern "C" {
48 #endif
49
50 /** creates the dualagg presolver and includes it in SCIP
51  *
52  * @ingroup PresolverIncludes
53  */
56  SCIP* scip /**< SCIP data structure */
57  );
58
59 #ifdef __cplusplus
60 }
61 #endif
62
63 #endif
#define SCIP_EXPORT
Definition: def.h:100
enum SCIP_Retcode SCIP_RETCODE
Definition: type_retcode.h:54
type definitions for return codes for SCIP methods
type definitions for SCIP&#39;s main datastructure
SCIP_EXPORT SCIP_RETCODE SCIPincludePresolDualagg(SCIP *scip)
common defines and data types used in all packages of SCIP