cuts.h

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/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/*                                                                           */
/*                  This file is part of the program and library             */
/*         SCIP --- Solving Constraint Integer Programs                      */
/*                                                                           */
/*    Copyright (C) 2002-2022 Konrad-Zuse-Zentrum                            */
/*                            fuer Informationstechnik Berlin                */
/*                                                                           */
/*  SCIP is distributed under the terms of the ZIB Academic License.         */
/*                                                                           */
/*  You should have received a copy of the ZIB Academic License              */
/*  along with SCIP; see the file COPYING. If not visit scipopt.org.         */
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/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/**@file   cuts.h
 * @ingroup PUBLICCOREAPI
 * @brief  methods for the aggregation rows
 * @author Jakob Witzig
 * @author Leona Gottwald
 *
 */

/*---+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0----+----1----+----2*/

#ifndef __SCIP_CUTS_H__
#define __SCIP_CUTS_H__

#include "scip/def.h"
#include "scip/struct_cuts.h"
#include "scip/type_cuts.h"
#include "scip/type_lp.h"
#include "scip/type_misc.h"
#include "scip/type_retcode.h"
#include "scip/type_scip.h"
#include "scip/type_sol.h"
#include "scip/type_var.h"

#ifdef __cplusplus
extern "C" {
#endif

/**@addtogroup PublicCutMethods
 *
 * @{
 */

/** perform activity based coefficient tigthening on the given cut; returns TRUE if the cut was detected
 *  to be redundant due to acitivity bounds
 *
 *  See also cons_linear.c:consdataTightenCoefs().
 */
SCIP_EXPORT
SCIP_Bool SCIPcutsTightenCoefficients(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_Bool             cutislocal,         /**< is the cut local? */
   SCIP_Real*            cutcoefs,           /**< array of the non-zero coefficients in the cut */
   SCIP_Real*            cutrhs,             /**< the right hand side of the cut */
   int*                  cutinds,            /**< array of the problem indices of variables with a non-zero coefficient in the cut */
   int*                  cutnnz,             /**< the number of non-zeros in the cut */
   int*                  nchgcoefs           /**< number of changed coefficients */
   );

/** create an empty the aggregation row */
SCIP_EXPORT
SCIP_RETCODE SCIPaggrRowCreate(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_AGGRROW**        aggrrow             /**< pointer to return the aggregation row */
   );

/** free a the aggregation row */
SCIP_EXPORT
void SCIPaggrRowFree(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_AGGRROW**        aggrrow             /**< pointer to the aggregation row that should be freed */
   );

/** output aggregation row to file stream */
SCIP_EXPORT
void SCIPaggrRowPrint(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_AGGRROW*         aggrrow,            /**< pointer to return aggregation row */
   FILE*                 file                /**< output file (or NULL for standard output) */
   );

/** copy the aggregation row */
SCIP_EXPORT
SCIP_RETCODE SCIPaggrRowCopy(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_AGGRROW**        aggrrow,            /**< pointer to return the aggregation row */
   SCIP_AGGRROW*         source              /**< source the aggregation row */
   );

/** add weighted row to the aggregation row */
SCIP_EXPORT
SCIP_RETCODE SCIPaggrRowAddRow(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row */
   SCIP_ROW*             row,                /**< row to add to the aggregation row */
   SCIP_Real             weight,             /**< scale for adding given row to the aggregation row */
   int                   sidetype            /**< specify row side type (-1 = lhs, 0 = automatic, 1 = rhs) */
   );

/** Removes a given variable @p var from position @p pos the aggregation row and updates the right-hand side according
 *  to sign of the coefficient, i.e., rhs -= coef * bound, where bound = lb if coef >= 0 and bound = ub, otherwise.
 *
 *  @note: The choice of global or local bounds depend on the validity (global or local) of the aggregation row.
 *
 *  @note: The list of non-zero indices will be updated by swapping the last non-zero index to @p pos.
 */
SCIP_EXPORT
void SCIPaggrRowCancelVarWithBound(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row */
   SCIP_VAR*             var,                /**< variable that should be removed */
   int                   pos,                /**< position of the variable in the aggregation row */
   SCIP_Bool*            valid               /**< pointer to return whether the aggregation row is still valid */
   );

/** add the objective function with right-hand side @p rhs and scaled by @p scale to the aggregation row */
SCIP_EXPORT
SCIP_RETCODE SCIPaggrRowAddObjectiveFunction(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row */
   SCIP_Real             rhs,                /**< right-hand side of the artificial row */
   SCIP_Real             scale               /**< scalar */
   );

/** add weighted constraint to the aggregation row */
SCIP_EXPORT
SCIP_RETCODE SCIPaggrRowAddCustomCons(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row */
   int*                  inds,               /**< variable problem indices in constraint to add to the aggregation row */
   SCIP_Real*            vals,               /**< values of constraint to add to the aggregation row */
   int                   len,                /**< length of constraint to add to the aggregation row */
   SCIP_Real             rhs,                /**< right hand side of constraint to add to the aggregation row */
   SCIP_Real             weight,             /**< (positive) scale for adding given constraint to the aggregation row */
   int                   rank,               /**< rank to use for given constraint */
   SCIP_Bool             local               /**< is constraint only valid locally */
   );

/** calculates the efficacy norm of the given aggregation row, which depends on the "separating/efficacynorm" parameter
 *
 *  @return the efficacy norm of the given aggregation row, which depends on the "separating/efficacynorm" parameter
 */
SCIP_EXPORT
SCIP_Real SCIPaggrRowCalcEfficacyNorm(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_AGGRROW*         aggrrow             /**< the aggregation row */
   );

/** clear all entries in the aggregation row but do not free the internal memory */
SCIP_EXPORT
void SCIPaggrRowClear(
   SCIP_AGGRROW*         aggrrow             /**< the aggregation row */
   );

/** aggregate rows using the given weights; the current content of the aggregation
 *  row, \p aggrrow, gets overwritten
 */
SCIP_EXPORT
SCIP_RETCODE SCIPaggrRowSumRows(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row */
   SCIP_Real*            weights,            /**< row weights in row summation */
   int*                  rowinds,            /**< array to store indices of non-zero entries of the weights array, or NULL */
   int                   nrowinds,           /**< number of non-zero entries in weights array, -1 if rowinds is NULL */
   SCIP_Bool             sidetypebasis,      /**< choose sidetypes of row (lhs/rhs) based on basis information? */
   SCIP_Bool             allowlocal,         /**< should local rows be used? */
   int                   negslack,           /**< should negative slack variables be used? (0: no, 1: only for integral rows, 2: yes) */
   int                   maxaggrlen,         /**< maximal number of non-zeros in the aggregation row */
   SCIP_Bool*            valid               /**< is the aggregation valid */
   );

/** removes all (close enough to) zero entries in the aggregation row */
SCIP_EXPORT
void SCIPaggrRowRemoveZeros(
   SCIP*                 scip,               /**< SCIP datastructure */
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row */
   SCIP_Bool             useglbbounds,       /**< consider global bound although the cut is local? */
   SCIP_Bool*            valid               /**< pointer to return whether the aggregation row is still valid */
   );

/** get array with lp positions of aggregated rows */
SCIP_EXPORT
int* SCIPaggrRowGetRowInds(
   SCIP_AGGRROW*         aggrrow             /**< the aggregation row */
   );

/** get array with weights of aggregated rows */
SCIP_EXPORT
SCIP_Real* SCIPaggrRowGetRowWeights(
   SCIP_AGGRROW*         aggrrow             /**< the aggregation row */
   );

/** checks whether a given row has been added to the aggregation row */
SCIP_EXPORT
SCIP_Bool SCIPaggrRowHasRowBeenAdded(
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row */
   SCIP_ROW*             row                 /**< row for which it is checked whether it has been added to the aggregation */
   );

/** gets the min and max absolute value of the weights used to aggregate the rows;
 *  must not be called for empty aggregation rows
 */
SCIP_EXPORT
void SCIPaggrRowGetAbsWeightRange(
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row */
   SCIP_Real*            minabsrowweight,    /**< pointer to store smallest absolute value of weights used for aggregating rows */
   SCIP_Real*            maxabsrowweight     /**< pointer to store largest absolute value of weights used for aggregating rows */
   );

/** gets the array of corresponding variable problem indices for each non-zero in the aggregation row */
SCIP_EXPORT
int* SCIPaggrRowGetInds(
    SCIP_AGGRROW*        aggrrow
   );

/** gets the number of non-zeros in the aggregation row */
SCIP_EXPORT
int SCIPaggrRowGetNNz(
   SCIP_AGGRROW*         aggrrow             /**< the aggregation row */
   );

/** gets the non-zero value for the given non-zero index */
static INLINE
SCIP_Real SCIPaggrRowGetValue(
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row */
   int                   i                   /**< non-zero index; must be between 0 and SCIPaggrRowGetNNz(aggrrow) - 1 */
   )
{
   SCIP_Real QUAD(val);

   QUAD_ARRAY_LOAD(val, aggrrow->vals, aggrrow->inds[i]);

   return QUAD_TO_DBL(val);
}

/** gets the non-zero value for the given problem index of a variable */
static INLINE
SCIP_Real SCIPaggrRowGetProbvarValue(
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row */
   int                   probindex           /**< problem index of variable; must be between 0 and SCIPgetNVars(scip) - 1 */
   )
{
   SCIP_Real QUAD(val);

   QUAD_ARRAY_LOAD(val, aggrrow->vals, probindex);

   return QUAD_TO_DBL(val);
}

/** gets the rank of the aggregation row */
SCIP_EXPORT
int SCIPaggrRowGetRank(
   SCIP_AGGRROW*         aggrrow             /**< the aggregation row */
   );

/** checks if the aggregation row is only valid locally */
SCIP_EXPORT
SCIP_Bool SCIPaggrRowIsLocal(
   SCIP_AGGRROW*         aggrrow             /**< the aggregation row */
   );

/** gets the right hand side of the aggregation row */
SCIP_EXPORT
SCIP_Real SCIPaggrRowGetRhs(
   SCIP_AGGRROW*         aggrrow             /**< the aggregation row */
   );

/** gets the number of row aggregations */
SCIP_EXPORT
int SCIPaggrRowGetNRows(
   SCIP_AGGRROW*         aggrrow             /**< aggregation row */
   );

/** calculates an MIR cut out of the weighted sum of LP rows given by an aggregation row; the
 *  aggregation row must not contain non-zero weights for modifiable rows, because these rows cannot
 *  participate in an MIR cut.
 *
 *  @return \ref SCIP_OKAY is returned if everything worked. Otherwise a suitable error code is passed. See \ref
 *          SCIP_Retcode "SCIP_RETCODE" for a complete list of error codes.
 *
 *  @pre This method can be called if @p scip is in one of the following stages:
 *       - \ref SCIP_STAGE_SOLVING
 *
 *  See \ref SCIP_Stage "SCIP_STAGE" for a complete list of all possible solving stages.
 */
SCIP_EXPORT
SCIP_RETCODE SCIPcalcMIR(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_SOL*             sol,                /**< the solution that should be separated, or NULL for LP solution */
   SCIP_Bool             postprocess,        /**< apply a post-processing step to the resulting cut? */
   SCIP_Real             boundswitch,        /**< fraction of domain up to which lower bound is used in transformation */
   SCIP_Bool             usevbds,            /**< should variable bounds be used in bound transformation? */
   SCIP_Bool             allowlocal,         /**< should local information allowed to be used, resulting in a local cut? */
   SCIP_Bool             fixintegralrhs,     /**< should complementation tried to be adjusted such that rhs gets fractional? */
   int*                  boundsfortrans,     /**< bounds that should be used for transformed variables: vlb_idx/vub_idx,
                                              *   -1 for global lb/ub, -2 for local lb/ub, or -3 for using closest bound;
                                              *   NULL for using closest bound for all variables */
   SCIP_BOUNDTYPE*       boundtypesfortrans, /**< type of bounds that should be used for transformed variables;
                                              *   NULL for using closest bound for all variables */
   SCIP_Real             minfrac,            /**< minimal fractionality of rhs to produce MIR cut for */
   SCIP_Real             maxfrac,            /**< maximal fractionality of rhs to produce MIR cut for */
   SCIP_Real             scale,              /**< additional scaling factor multiplied to the aggrrow; must be positive */
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row to compute an MIR cut for */
   SCIP_Real*            cutcoefs,           /**< array to store the non-zero coefficients in the cut */
   SCIP_Real*            cutrhs,             /**< pointer to store the right hand side of the cut */
   int*                  cutinds,            /**< array to store the problem indices of variables with a non-zero coefficient in the cut */
   int*                  cutnnz,             /**< pointer to store the number of non-zeros in the cut */
   SCIP_Real*            cutefficacy,        /**< pointer to store the efficacy of the cut, or NULL */
   int*                  cutrank,            /**< pointer to return rank of generated cut */
   SCIP_Bool*            cutislocal,         /**< pointer to store whether the generated cut is only valid locally */
   SCIP_Bool*            success             /**< pointer to store whether the returned coefficients are a valid MIR cut */
   );

/** calculates an MIR cut out of the weighted sum of LP rows given by an aggregation row; the
 *  aggregation row must not contain non-zero weights for modifiable rows, because these rows cannot
 *  participate in an MIR cut. The function uses a cut generation heuristic which tries different scaling
 *  factors and complementations of the variables to improve the cut's efficacy.
 *  For further details we refer to:
 *
 *  Marchand, H., & Wolsey, L. A. (2001). Aggregation and mixed integer rounding to solve MIPs.
 *  Operations research, 49(3), 363-371.
 *
 *  @return \ref SCIP_OKAY is returned if everything worked. Otherwise a suitable error code is passed. See \ref
 *          SCIP_Retcode "SCIP_RETCODE" for a complete list of error codes.
 *
 *  @pre This method can be called if @p scip is in one of the following stages:
 *       - \ref SCIP_STAGE_SOLVING
 *
 *  See \ref SCIP_Stage "SCIP_STAGE" for a complete list of all possible solving stages.
 */
SCIP_EXPORT
SCIP_RETCODE SCIPcutGenerationHeuristicCMIR(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_SOL*             sol,                /**< the solution that should be separated, or NULL for LP solution */
   SCIP_Bool             postprocess,        /**< apply a post-processing step to the resulting cut? */
   SCIP_Real             boundswitch,        /**< fraction of domain up to which lower bound is used in transformation */
   SCIP_Bool             usevbds,            /**< should variable bounds be used in bound transformation? */
   SCIP_Bool             allowlocal,         /**< should local information allowed to be used, resulting in a local cut? */
   int                   maxtestdelta,       /**< maximum number of deltas to test */
   int*                  boundsfortrans,     /**< bounds that should be used for transformed variables: vlb_idx/vub_idx,
                                              *   -1 for global lb/ub, -2 for local lb/ub, or -3 for using closest bound;
                                              *   NULL for using closest bound for all variables */
   SCIP_BOUNDTYPE*       boundtypesfortrans, /**< type of bounds that should be used for transformed variables;
                                              *   NULL for using closest bound for all variables */
   SCIP_Real             minfrac,            /**< minimal fractionality of rhs to produce MIR cut for */
   SCIP_Real             maxfrac,            /**< maximal fractionality of rhs to produce MIR cut for */
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row to compute MIR cut for */
   SCIP_Real*            cutcoefs,           /**< array to store the non-zero coefficients in the cut */
   SCIP_Real*            cutrhs,             /**< pointer to store the right hand side of the cut */
   int*                  cutinds,            /**< array to store the problem indices of variables with a non-zero coefficient in the cut */
   int*                  cutnnz,             /**< pointer to store the number of non-zeros in the cut */
   SCIP_Real*            cutefficacy,        /**< pointer to store efficacy of best cut; only cuts that are strictly better than the value of
                                              *   this efficacy on input to this function are returned */
   int*                  cutrank,            /**< pointer to return rank of generated cut */
   SCIP_Bool*            cutislocal,         /**< pointer to store whether the generated cut is only valid locally */
   SCIP_Bool*            success             /**< pointer to store whether a valid and efficacious cut was returned */
   );

/** calculates a lifted simple generalized flow cover cut out of the weighted sum of LP rows given by an aggregation row; the
 *  aggregation row must not contain non-zero weights for modifiable rows, because these rows cannot
 *  participate in the cut.
 *  For further details we refer to:
 *
 *  Gu, Z., Nemhauser, G. L., & Savelsbergh, M. W. (1999). Lifted flow cover inequalities for mixed 0-1 integer programs.
 *  Mathematical Programming, 85(3), 439-467.
 *
 *  @return \ref SCIP_OKAY is returned if everything worked. Otherwise a suitable error code is passed. See \ref
 *          SCIP_Retcode "SCIP_RETCODE" for a complete list of error codes.
 *
 *  @pre This method can be called if @p scip is in one of the following stages:
 *       - \ref SCIP_STAGE_SOLVING
 *
 *  See \ref SCIP_Stage "SCIP_STAGE" for a complete list of all possible solving stages.
 */
SCIP_EXPORT
SCIP_RETCODE SCIPcalcFlowCover(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_SOL*             sol,                /**< the solution that should be separated, or NULL for LP solution */
   SCIP_Bool             postprocess,        /**< apply a post-processing step to the resulting cut? */
   SCIP_Real             boundswitch,        /**< fraction of domain up to which lower bound is used in transformation */
   SCIP_Bool             allowlocal,         /**< should local information allowed to be used, resulting in a local cut? */
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row to compute flow cover cut for */
   SCIP_Real*            cutcoefs,           /**< array to store the non-zero coefficients in the cut */
   SCIP_Real*            cutrhs,             /**< pointer to store the right hand side of the cut */
   int*                  cutinds,            /**< array to store the problem indices of variables with a non-zero coefficient in the cut */
   int*                  cutnnz,             /**< pointer to store the number of non-zeros in the cut */
   SCIP_Real*            cutefficacy,        /**< pointer to store the efficacy of the cut, or NULL */
   int*                  cutrank,            /**< pointer to return rank of generated cut */
   SCIP_Bool*            cutislocal,         /**< pointer to store whether the generated cut is only valid locally */
   SCIP_Bool*            success             /**< pointer to store whether a valid cut was returned */
   );

/** calculates a lifted knapsack cover cut out of the weighted sum of LP rows given by an aggregation row; the
 *  aggregation row must not contain non-zero weights for modifiable rows, because these rows cannot
 *  participate in the cut.
 *  For further details we refer to:
 *
 *  Letchford, A. N., & Souli, G. (2019). On lifted cover inequalities: A new lifting procedure with unusual properties.
 *  Operations Research Letters, 47(2), 83-87.
 *
 *  @return \ref SCIP_OKAY is returned if everything worked. Otherwise a suitable error code is passed. See \ref
 *          SCIP_Retcode "SCIP_RETCODE" for a complete list of error codes.
 *
 *  @pre This method can be called if @p scip is in one of the following stages:
 *       - \ref SCIP_STAGE_SOLVING
 *
 *  See \ref SCIP_Stage "SCIP_STAGE" for a complete list of all possible solving stages.
 */
SCIP_EXPORT
SCIP_RETCODE SCIPcalcKnapsackCover(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_SOL*             sol,                /**< the solution that should be separated, or NULL for LP solution */
   SCIP_Bool             allowlocal,         /**< should local information allowed to be used, resulting in a local cut? */
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row to compute flow cover cut for */
   SCIP_Real*            cutcoefs,           /**< array to store the non-zero coefficients in the cut */
   SCIP_Real*            cutrhs,             /**< pointer to store the right hand side of the cut */
   int*                  cutinds,            /**< array to store the problem indices of variables with a non-zero coefficient in the cut */
   int*                  cutnnz,             /**< pointer to store the number of non-zeros in the cut */
   SCIP_Real*            cutefficacy,        /**< pointer to store the efficacy of the cut, or NULL */
   int*                  cutrank,            /**< pointer to return rank of generated cut */
   SCIP_Bool*            cutislocal,         /**< pointer to store whether the generated cut is only valid locally */
   SCIP_Bool*            success             /**< pointer to store whether a valid cut was returned */
   );

/** calculates a strong CG cut out of the weighted sum of LP rows given by an aggregation row; the
 *  aggregation row must not contain non-zero weights for modifiable rows, because these rows cannot
 *  participate in a strongcg cut
 *
 *  @return \ref SCIP_OKAY is returned if everything worked. Otherwise a suitable error code is passed. See \ref
 *          SCIP_Retcode "SCIP_RETCODE" for a complete list of error codes.
 *
 *  @pre This method can be called if @p scip is in one of the following stages:
 *       - \ref SCIP_STAGE_SOLVING
 *
 *  See \ref SCIP_Stage "SCIP_STAGE" for a complete list of all possible solving stages.
 */
SCIP_EXPORT
SCIP_RETCODE SCIPcalcStrongCG(
   SCIP*                 scip,               /**< SCIP data structure */
   SCIP_SOL*             sol,                /**< the solution that should be separated, or NULL for LP solution */
   SCIP_Bool             postprocess,        /**< apply a post-processing step to the resulting cut? */
   SCIP_Real             boundswitch,        /**< fraction of domain up to which lower bound is used in transformation */
   SCIP_Bool             usevbds,            /**< should variable bounds be used in bound transformation? */
   SCIP_Bool             allowlocal,         /**< should local information allowed to be used, resulting in a local cut? */
   SCIP_Real             minfrac,            /**< minimal fractionality of rhs to produce strong CG cut for */
   SCIP_Real             maxfrac,            /**< maximal fractionality of rhs to produce strong CG cut for */
   SCIP_Real             scale,              /**< additional scaling factor multiplied to all rows */
   SCIP_AGGRROW*         aggrrow,            /**< the aggregation row to compute a strong CG cut for */
   SCIP_Real*            cutcoefs,           /**< array to store the non-zero coefficients in the cut */
   SCIP_Real*            cutrhs,             /**< pointer to store the right hand side of the cut */
   int*                  cutinds,            /**< array to store the problem indices of variables with a non-zero coefficient in the cut */
   int*                  cutnnz,             /**< pointer to store the number of non-zeros in the cut */
   SCIP_Real*            cutefficacy,        /**< pointer to store the efficacy of the cut, or NULL */
   int*                  cutrank,            /**< pointer to return rank of generated cut */
   SCIP_Bool*            cutislocal,         /**< pointer to store whether the generated cut is only valid locally */
   SCIP_Bool*            success             /**< pointer to store whether a valid cut was returned */
   );

/** @} */

#ifdef __cplusplus
}
#endif

#endif