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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11   	/*                                                                           */
12   	/*      http://www.apache.org/licenses/LICENSE-2.0                           */
13   	/*                                                                           */
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15   	/*  distributed under the License is distributed on an "AS IS" BASIS,        */
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18   	/*  limitations under the License.                                           */
19   	/*                                                                           */
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
66   	SCIP_RETCODE SCIPincludePresolDualsparsify(
67   	   SCIP*                 scip                /**< SCIP data structure */
68   	   );
69   	
70   	#ifdef __cplusplus
71   	}
72   	#endif
73   	
74   	#endif
75