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+// Last edit: 04/03/10
+//
+// Name: CglRedSplit2.hpp
+// Author: Giacomo Nannicini
+// Singapore University of Technology and Design
+// Singapore
+// email: nannicini@sutd.edu.sg
+// based on CglRedSplit by Francois Margot
+// Date: 03/09/09
+//-----------------------------------------------------------------------------
+// Copyright (C) 2010, Giacomo Nannicini and others. All Rights Reserved.
+
+#ifndef CglRedSplit2_H
+#define CglRedSplit2_H
+
+#include "CglCutGenerator.hpp"
+#include "CglRedSplit2Param.hpp"
+#include "CoinWarmStartBasis.hpp"
+#include "CoinHelperFunctions.hpp"
+#include "CoinTime.hpp"
+
+/** Reduce-and-Split Cut Generator Class; See method generateCuts().
+ Based on the papers "Practical strategies for generating rank-1
+ split cuts in mixed-integer linear programming" by G. Cornuejols
+ and G. Nannicini, published on Mathematical Programming
+ Computation, and "Combining Lift-and-Project and Reduce-and-Split"
+ by E. Balas, G. Cornuejols, T. Kis and G. Nannicini, published on
+ INFORMS Journal on Computing. Part of this code is based on
+ CglRedSplit by F. Margot. */
+
+class CglRedSplit2 : public CglCutGenerator {
+
+ friend void CglRedSplit2UnitTest(const OsiSolverInterface * siP,
+ const std::string mpdDir);
+public:
+ /**@name generateCuts */
+ //@{
+ /** Generate Reduce-and-Split Mixed Integer Gomory cuts
+ for the model of the solver interface si.
+
+ Insert the generated cuts into OsiCuts cs.
+
+ This generator currently works only with the Lp solvers Clp or
+ Cplex9.0 or higher. It requires access to the optimal tableau
+ and optimal basis inverse and makes assumptions on the way slack
+ variables are added by the solver. The Osi implementations for
+ Clp and Cplex verify these assumptions.
+
+ When calling the generator, the solver interface si must contain
+ an optimized problem and information related to the optimal
+ basis must be available through the OsiSolverInterface methods
+ (si->optimalBasisIsAvailable() must return 'true'). It is also
+ essential that the integrality of structural variable i can be
+ obtained using si->isInteger(i).
+
+ Reduce-and-Split cuts are a class of split cuts. We compute
+ linear combinations of the rows of the simplex tableau, trying
+ to reduce some of the coefficients on the nonbasic continuous
+ columns. We have a large number of heuristics to choose which
+ coefficients should be reduced, and by using which rows. The
+ paper explains everything in detail.
+
+ Note that this generator can potentially generate a huge number
+ of cuts, depending on how it is parametered. Default parameters
+ should be good for most situations; if you want to go heavy on
+ split cuts, use more row selection strategies or a different
+ number of rows in the linear combinations. Again, look at the
+ paper for details. If you want to generate a small number of
+ cuts, default parameters are not the best choice.
+
+ A combination of Reduce-and-Split with Lift & Project is
+ described in the paper "Combining Lift-and-Project and
+ Reduce-and-Split". The Reduce-and-Split code for the
+ implementation used in that paper is included here.
+
+ This generator does not generate the same cuts as CglRedSplit,
+ therefore both generators can be used in conjunction.
+
+ */
+
+ virtual void generateCuts(const OsiSolverInterface & si, OsiCuts & cs,
+ const CglTreeInfo info = CglTreeInfo());
+
+ /// Return true if needs optimal basis to do cuts (will return true)
+ virtual bool needsOptimalBasis() const;
+
+ // Generate the row multipliers computed by Reduce-and-Split from the
+ // given OsiSolverInterface. The multipliers are written in lambda;
+ // lambda should be of size nrow*maxNumMultipliers. We generate at most
+ // maxNumMultipliers m-vectors of row multipliers, and return the number
+ // of m-vectors that were generated.
+ // If the caller wants to know which variables are basic in each row
+ // (same order as lambda), basicVariables should be non-NULL (size nrow).
+ // This method can also generate the cuts corresponding to the multipliers
+ // returned; it suffices to pass non-NULL OsiCuts.
+ // This method is not needed by the typical user; however, it is useful
+ // in the context of generating Lift & Project cuts.
+ int generateMultipliers(const OsiSolverInterface& si, int* lambda,
+ int maxNumMultipliers, int* basicVariables = NULL,
+ OsiCuts* cs = NULL);
+
+ // Try to improve a Lift & Project cut, by employing the
+ // Reduce-and-Split procedure. We start from a row of a L&P tableau,
+ // and generate a cut trying to reduce the coefficients on the
+ // nonbasic variables. Note that this L&P tableau will in general
+ // have nonbasic variables which are nonzero in the point that we
+ // want to cut off, so we should be careful. Arguments:
+ // OsiSolverInterface which contains the simplex tableau, initial
+ // row from which the cut is derived, row rhs, row number of the
+ // source row (if it is in the simplex tableau; otherwise, a
+ // negative number; needed to avoid using duplicate rows), point
+ // that we want to cut off (note: this is NOT a basic solution for
+ // the OsiSolverInterace!), list of variables which are basic in
+ // xbar but are nonbasic in the OsiSolverInterface. The computed cut
+ // is written in OsiRowCut* cs. Finally, if a starting disjunction
+ // is provided in the vector lambda (of size ncols, i.e. a
+ // disjunction on the structural variables), the disjunction is
+ // modified according to the cut which is produced.
+ int tiltLandPcut(const OsiSolverInterface* si, double* row,
+ double rowRhs, int rownumber, const double* xbar,
+ const int* newnonbasics, OsiRowCut* cs, int* lambda = NULL);
+
+ //@}
+
+
+ /**@name Public Methods */
+ //@{
+
+ // Set the parameters to the values of the given CglRedSplit2Param object.
+ void setParam(const CglRedSplit2Param &source);
+ // Return the CglRedSplit2Param object of the generator.
+ inline CglRedSplit2Param& getParam() {return param;}
+
+ /// Print some of the data members; used for debugging
+ void print() const;
+
+ /// Print the current simplex tableau
+ void printOptTab(OsiSolverInterface *solver) const;
+
+ //@}
+
+ /**@name Constructors and destructors */
+ //@{
+ /// Default constructor
+ CglRedSplit2();
+
+ /// Constructor with specified parameters
+ CglRedSplit2(const CglRedSplit2Param &RS_param);
+
+ /// Copy constructor
+ CglRedSplit2(const CglRedSplit2 &);
+
+ /// Clone
+ virtual CglCutGenerator * clone() const;
+
+ /// Assignment operator
+ CglRedSplit2 & operator=(const CglRedSplit2& rhs);
+
+ /// Destructor
+ virtual ~CglRedSplit2 ();
+
+ //@}
+
+private:
+
+ // Private member methods
+
+/**@name Private member methods */
+
+ //@{
+
+ // Method generating the cuts after all CglRedSplit2 members are
+ // properly set. This does the actual work. Returns the number of
+ // generated cuts (or multipliers).
+ // Will generate cuts if cs != NULL, and will generate multipliers
+ // if lambda != NULL.
+ int generateCuts(OsiCuts* cs, int maxNumCuts, int* lambda = NULL);
+
+ /// Compute the fractional part of value, allowing for small error.
+ inline double rs_above_integer(const double value) const;
+
+ /// Fill workNonBasicTab, depending on the column selection strategy.
+ /// Accepts a list of variables indices that should be ignored; by
+ /// default, this list is empty (it is only used by Lift & Project).
+ /// The list ignore_list contains -1 as the last element.
+ /// Note that the implementation of the ignore_list is not very efficient
+ /// if the list is long, so it should be used only if its short.
+ void fill_workNonBasicTab(CglRedSplit2Param::ColumnSelectionStrategy
+ strategy, const int* ignore_list = NULL);
+
+ /// Fill workNonBasicTab, alternate version for Lift & Project: also
+ /// reduces columns which are now nonbasic but are basic in xbar.
+ /// This function should be called only when CglRedSplit2 is used in
+ /// conjunction with CglLandP to generate L&P+RS cuts.
+ void fill_workNonBasicTab(const int* newnonbasics, const double* xbar,
+ CglRedSplit2Param::ColumnScalingStrategy scaling);
+
+ /// Reduce rows of workNonBasicTab, i.e. compute integral linear
+ /// combinations of the rows in order to reduce row coefficients on
+ /// workNonBasicTab
+ void reduce_workNonBasicTab(int numRows,
+ CglRedSplit2Param::RowSelectionStrategy
+ rowSelectionStrategy,
+ int maxIterations);
+
+ /// Generate a linear combination of the rows of the current LP
+ /// tableau, using the row multipliers stored in the matrix pi_mat
+ /// on the row of index index_row
+ void generate_row(int index_row, double *row);
+
+ /// Generate a mixed integer Gomory cut, when all non basic
+ /// variables are non negative and at their lower bound.
+ int generate_cgcut(double *row, double *rhs);
+
+ /// Use multiples of the initial inequalities to cancel out the coefficients
+ /// of the slack variables.
+ void eliminate_slacks(double *row,
+ const double *elements,
+ const int *start,
+ const int *indices,
+ const int *rowLength,
+ const double *rhs, double *rowrhs);
+
+ /// Change the sign of the coefficients of the continuous non basic
+ /// variables at their upper bound.
+ void flip(double *row);
+
+ /// Change the sign of the coefficients of the continuous non basic
+ /// variables at their upper bound and do the translations restoring
+ /// the original bounds. Modify the right hand side
+ /// accordingly.
+ void unflip(double *row, double *rowrhs);
+
+ /// Returns 1 if the row has acceptable max/min coeff ratio.
+ /// Compute max_coeff: maximum absolute value of the coefficients.
+ /// Compute min_coeff: minimum absolute value of the coefficients
+ /// larger than EPS_COEFF.
+ /// Return 0 if max_coeff/min_coeff > MAXDYN.
+ int check_dynamism(double *row);
+
+ /// Generate the packed cut from the row representation.
+ int generate_packed_row(const double *xlp, double *row,
+ int *rowind, double *rowelem,
+ int *card_row, double & rhs);
+
+ // Compute entries of is_integer.
+ void compute_is_integer();
+
+ // Check that two vectors are different.
+ bool rs_are_different_vectors(const int *vect1,
+ const int *vect2,
+ const int dim);
+
+ // allocate matrix of integers
+ void rs_allocmatINT(int ***v, int m, int n);
+ // deallocate matrix of integers
+ void rs_deallocmatINT(int ***v, int m);
+ // allocate matrix of doubles
+ void rs_allocmatDBL(double ***v, int m, int n);
+ // deallocate matrix of doubles
+ void rs_deallocmatDBL(double ***v, int m);
+ // print a vector of integers
+ void rs_printvecINT(const char *vecstr, const int *x, int n) const;
+ // print a vector of doubles
+ void rs_printvecDBL(const char *vecstr, const double *x, int n) const;
+ // print a matrix of integers
+ void rs_printmatINT(const char *vecstr, const int * const *x, int m, int n) const;
+ // print a matrix of doubles
+ void rs_printmatDBL(const char *vecstr, const double * const *x, int m, int n) const;
+ // dot product
+ double rs_dotProd(const double *u, const double *v, int dim) const;
+ double rs_dotProd(const int *u, const double *v, int dim) const;
+ // From Numerical Recipes in C: LU decomposition
+ int ludcmp(double **a, int n, int *indx, double *d, double* vv) const;
+ // from Numerical Recipes in C: backward substitution
+ void lubksb(double **a, int n, int *indx, double *b) const;
+
+ // Check if the linear combination given by listOfRows with given multipliers
+ // improves the norm of row #rowindex; note: multipliers are rounded!
+ // Returns the difference with respect to the old norm (if negative there is
+ // an improvement, if positive norm increases)
+ double compute_norm_change(double oldnorm, const int* listOfRows,
+ int numElemList, const double* multipliers) const;
+
+ // Compute the list of rows that should be used to reduce row #rowIndex
+ int get_list_rows_reduction(int rowIndex, int numRowsReduction,
+ int* list, const double* norm,
+ CglRedSplit2Param::RowSelectionStrategy
+ rowSelectionStrategy) const;
+
+ // Sorts the rows by increasing number of nonzeroes with respect to a given
+ // row (rowIndex), on the nonbasic variables (whichTab == 0 means only
+ // integer, whichTab == 1 means only workTab, whichTab == 2 means both).
+ // The array for sorting must be allocated (and deleted) by caller.
+ // Corresponds to BRS1 in the paper.
+ int sort_rows_by_nonzeroes(struct sortElement* array, int rowIndex,
+ int maxRows, int whichTab) const;
+
+ // Greedy variant of the previous function; slower but typically
+ // more effective. Corresponds to BRS2 in the paper.
+ int sort_rows_by_nonzeroes_greedy(struct sortElement* array, int rowIndex,
+ int maxRows, int whichTab) const;
+
+ // Sorts the rows by decreasing absolute value of the cosine of the
+ // angle with respect to a given row (rowIndex), on the nonbasic
+ // variables (whichTab == 0 means only integer, whichTab == 1 means
+ // only workTab, whichTab == 2 means both). The array for sorting
+ // must be allocated (and deleted) by caller. Very effective
+ // strategy in practice. Corresponds to BRS3 in the paper.
+ int sort_rows_by_cosine(struct sortElement* array, int rowIndex,
+ int maxRows, int whichTab) const;
+
+ // Did we hit the time limit?
+ inline bool checkTime() const{
+ if ((CoinCpuTime() - startTime) < param.getTimeLimit()){
+ return true;
+ }
+ return false;
+ }
+
+ //@}
+
+
+ // Private member data
+
+ /**@name Private member data */
+
+ //@{
+
+ /// Object with CglRedSplit2Param members.
+ CglRedSplit2Param param;
+
+ /// Number of rows ( = number of slack variables) in the current LP.
+ int nrow;
+
+ /// Number of structural variables in the current LP.
+ int ncol;
+
+ /// Number of rows which have been reduced
+ int numRedRows;
+
+ /// Lower bounds for structural variables
+ const double *colLower;
+
+ /// Upper bounds for structural variables
+ const double *colUpper;
+
+ /// Lower bounds for constraints
+ const double *rowLower;
+
+ /// Upper bounds for constraints
+ const double *rowUpper;
+
+ /// Righ hand side for constraints (upper bound for ranged constraints).
+ const double *rowRhs;
+
+ /// Reduced costs for columns
+ const double *reducedCost;
+
+ /// Row price
+ const double *rowPrice;
+
+ /// Objective coefficients
+ const double* objective;
+
+ /// Number of integer basic structural variables
+ int card_intBasicVar;
+
+ /// Number of integer basic structural variables that are fractional in the
+ /// current lp solution (at least param.away_ from being integer).
+ int card_intBasicVar_frac;
+
+ /// Number of integer non basic structural variables in the
+ /// current lp solution.
+ int card_intNonBasicVar;
+
+ /// Number of continuous non basic variables (structural or slack) in the
+ /// current lp solution.
+ int card_contNonBasicVar;
+
+ /// Number of continuous non basic variables (structural or slack) in the
+ /// current working set for coefficient reduction
+ int card_workNonBasicVar;
+
+ /// Number of non basic variables (structural or slack) at their
+ /// upper bound in the current lp solution.
+ int card_nonBasicAtUpper;
+
+ /// Number of non basic variables (structural or slack) at their
+ /// lower bound in the current lp solution.
+ int card_nonBasicAtLower;
+
+ /// Characteristic vector for integer basic structural variables
+ int *cv_intBasicVar;
+
+ /// Characteristic vector for integer basic structural variables
+ /// with non integer value in the current lp solution.
+ int *cv_intBasicVar_frac;
+
+ /// Characteristic vector for rows of the tableau selected for reduction
+ /// with non integer value in the current lp solution
+ int *cv_fracRowsTab;
+
+ /// List of integer structural basic variables
+ /// (in order of pivot in selected rows for cut generation).
+ int *intBasicVar;
+
+ /// List of integer structural basic variables with fractional value
+ /// (in order of pivot in selected rows for cut generation).
+ int *intBasicVar_frac;
+
+ /// List of integer structural non basic variables.
+ int *intNonBasicVar;
+
+ /// List of continuous non basic variables (structural or slack).
+ // slacks are considered continuous (no harm if this is not the case).
+ int *contNonBasicVar;
+
+ /// List of non basic variables (structural or slack) at their
+ /// upper bound.
+ int *nonBasicAtUpper;
+
+ /// List of non basic variables (structural or slack) at their lower
+ /// bound.
+ int *nonBasicAtLower;
+
+ /// Number of rows in the reduced tableau (= card_intBasicVar).
+ int mTab;
+
+ /// Number of columns in the reduced tableau (= card_contNonBasicVar)
+ int nTab;
+
+ /// Tableau of multipliers used to alter the rows used in generation.
+ /// Dimensions: mTab by mTab. Initially, pi_mat is the identity matrix.
+ int **pi_mat;
+
+ /// Simplex tableau for continuous non basic variables (structural or slack).
+ /// Only rows used for generation.
+ /// Dimensions: mTab by card_contNonBasicVar.
+ double **contNonBasicTab;
+
+ /// Current tableau for continuous non basic variables (structural or slack).
+ /// Only columns used for coefficient reduction.
+ /// Dimensions: mTab by card_workNonBasicVar.
+ double **workNonBasicTab;
+
+ /// Simplex tableau for integer non basic structural variables.
+ /// Only rows used for generation.
+ // Dimensions: mTab by card_intNonBasicVar.
+ double **intNonBasicTab;
+
+ /// Right hand side of the tableau.
+ /// Only rows used for generation.
+ double *rhsTab;
+
+ /// Norm of rows in workNonBasicTab; needed for faster computations
+ double *norm;
+
+ /// Characteristic vectors of structural integer variables or continuous
+ /// variables currently fixed to integer values.
+ int *is_integer;
+
+ /// Pointer on solver. Reset by each call to generateCuts().
+ OsiSolverInterface *solver;
+
+ /// Pointer on point to separate. Reset by each call to generateCuts().
+ const double *xlp;
+
+ /// Pointer on row activity. Reset by each call to generateCuts().
+ const double *rowActivity;
+
+ /// Pointer on matrix of coefficient ordered by rows.
+ /// Reset by each call to generateCuts().
+ const CoinPackedMatrix *byRow;
+
+ /// Time at which cut computations began.
+ /// Reset by each call to generateCuts().
+ double startTime;
+
+ //@}
+};
+
+//#############################################################################
+/** A function that tests some of the methods in the CglRedSplit2
+ class. The only reason for it not to be a member method is that
+ this way it doesn't have to be compiled into the library. And
+ that's a gain, because the library should be compiled with
+ optimization on, but this method should be compiled with
+ debugging. */
+void CglRedSplit2UnitTest(const OsiSolverInterface * siP,
+ const std::string mpdDir );
+
+
+#endif