Scippy

SCIP

Solving Constraint Integer Programs

presol_dualsparsify.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) 2002-2023 Zuse Institute Berlin (ZIB) */
7 /* */
8 /* Licensed under the Apache License, Version 2.0 (the "License"); */
9 /* you may not use this file except in compliance with the License. */
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20 /* You should have received a copy of the Apache-2.0 license */
21 /* along with SCIP; see the file LICENSE. If not visit scipopt.org. */
22 /* */
23 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
24 
25 /**@file presol_dualsparsify.h
26  * @brief cancel nonzeros of the constraint matrix based on the columns
27  * @author Dieter Weninger
28  * @author Leona Gottwald
29  * @author Ambros Gleixner
30  * @author Weikun Chen
31  *
32  * This presolver attempts to cancel non-zero entries of the constraint
33  * matrix by adding scaled columns to other columns.
34  *
35  * In more detail, for two columns A_{j.} and A_{k.}, suppose for a given value s, we have
36  *
37  * | A_{j.} | - | A_{j.} - s*A_{k.} | > eta,
38  *
39  * where eta is an nonnegative integer. Then we introduce a new variable y := s*x_j + x_k
40  * and aggregate the variable x_k = y - s*x_j. After aggregation, the column of the variable
41  * x_j is A_{j.} + s*A_{j.} which is sparser than A_{j.}. In the case that x_k is no implied
42  * free variable, we need to add a new constraint l_k <= y - weight*x_j <= u_k into the problem
43  * to keep the bounds constraints of variable x_k.
44  *
45  * Further information can be found in
46  * Chen et al. "Two-row and two-column mixed-integer presolve using hasing-based pairing methods".
47  *
48  * @todo add infrastructure to SCIP for handling aggregated binary variables
49  */
50 
51 /*---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0----+----1----+----2*/
52 
53 #ifndef __SCIP_PRESOL_DUALSPARSIFY_H__
54 #define __SCIP_PRESOL_DUALSPARSIFY_H__
55 
56 #include "scip/def.h"
57 #include "scip/type_retcode.h"
58 #include "scip/type_scip.h"
59 
60 #ifdef __cplusplus
61 extern "C" {
62 #endif
63 
64 /** creates the dual sparsify presolver and includes it in SCIP */
65 SCIP_EXPORT
67  SCIP* scip /**< SCIP data structure */
68  );
69 
70 #ifdef __cplusplus
71 }
72 #endif
73 
74 #endif
enum SCIP_Retcode SCIP_RETCODE
Definition: type_retcode.h:63
type definitions for return codes for SCIP methods
SCIP_RETCODE SCIPincludePresolDualsparsify(SCIP *scip)
type definitions for SCIP&#39;s main datastructure
common defines and data types used in all packages of SCIP