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_dualinfer.h
17  * @ingroup PRESOLVERS
18  * @brief  dual inference presolver
19  * @author Dieter Weninger
20  * @author Patrick Gemander
21  *
22  * This presolver does bound strengthening on continuous variables (columns) for getting bounds on dual variables y.
23  * The bounds of the dual variables are then used to fix primal variables or change the side of constraints.
24  * For ranged rows one needs to decide which side (rhs or lhs) determines the equality.
25  *
26  * We distinguish two cases concerning complementary slackness:
27  * i)  reduced cost fixing:       c_j - sup_y(y^T A_{.j}) > 0 => x_j = l_j
28  *                                c_j - inf_y(y^T A_{.j}) < 0 => x_j = u_j
29  * ii) positive dual lower bound: y_i > 0 =>  A_{i.}x = b_i
30  *
31  * Further information on this presolving approach are given in
32  * Achterberg et al. "Presolve reductions in mixed integer programming"
33  * and for a two-column extension in
34  * Chen et al. "Two-row and two-column mixed-integer presolve using hasing-based pairing methods".
35  */
36 
37 /*---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0----+----1----+----2*/
38 
39 #ifndef __SCIP_PRESOL_DUALINFER_H__
40 #define __SCIP_PRESOL_DUALINFER_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 dual inference presolver and includes it in SCIP
51  *
52  * @ingroup PresolverIncludes
53  */
54 SCIP_EXPORT
55 SCIP_RETCODE SCIPincludePresolDualinfer(
56    SCIP*                 scip                /**< SCIP data structure */
57    );
58 
59 #ifdef __cplusplus
60 }
61 #endif
62 
63 #endif
64