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+// Last edit: 4/20/07
+//
+// Name: CglRedSplit.hpp
+// Author: Francois Margot
+// Tepper School of Business
+// Carnegie Mellon University, Pittsburgh, PA 15213
+// email: fmargot@andrew.cmu.edu
+// Date: 2/6/05
+//
+// $Id: CglRedSplit.hpp 1119 2013-04-06 20:24:18Z stefan $
+//-----------------------------------------------------------------------------
+// Copyright (C) 2005, Francois Margot and others. All Rights Reserved.
+// This code is licensed under the terms of the Eclipse Public License (EPL).
+
+#ifndef CglRedSplit_H
+#define CglRedSplit_H
+
+#include "CglCutGenerator.hpp"
+#include "CglRedSplitParam.hpp"
+
+/** Gomory Reduce-and-Split Cut Generator Class; See method generateCuts().
+ Based on the paper by K. Anderson, G. Cornuejols, Yanjun Li,
+ "Reduce-and-Split Cuts: Improving the Performance of Mixed Integer
+ Gomory Cuts", Management Science 51 (2005). */
+
+class CglRedSplit : public CglCutGenerator {
+
+ friend void CglRedSplitUnitTest(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.
+
+ Warning: 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 variants of Gomory cuts: Starting from
+ the current optimal tableau, linear combinations of the rows of
+ the current optimal simplex tableau are used for generating Gomory
+ cuts. The choice of the linear combinations is driven by the objective
+ of reducing the coefficients of the non basic continuous variables
+ in the resulting row.
+ Note that this generator might not be able to generate cuts for some
+ solutions violating integrality constraints.
+
+ */
+ 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;
+ //@}
+
+
+ /**@name Public Methods */
+ //@{
+
+ // Set the parameters to the values of the given CglRedSplitParam object.
+ void setParam(const CglRedSplitParam &source);
+ // Return the CglRedSplitParam object of the generator.
+ inline CglRedSplitParam getParam() const {return param;}
+
+ // Compute entries of low_is_lub and up_is_lub.
+ void compute_is_lub();
+
+ // Compute entries of is_integer.
+ void compute_is_integer();
+
+ /// Set given_optsol to the given optimal solution given_sol.
+ /// If given_optsol is set using this method,
+ /// the code will stop as soon as
+ /// a generated cut is violated by the given solution; exclusively
+ /// for debugging purposes.
+ void set_given_optsol(const double *given_sol, const int card_sol);
+
+ /// Print some of the data members
+ void print() const;
+
+ /// Print the current simplex tableau
+ void printOptTab(OsiSolverInterface *solver) const;
+
+ //@}
+
+ /**@name Public Methods (soon to be obsolete)*/
+ //@{
+ //************************************************************
+ // TO BE REMOVED
+ /** Set limit, the maximum number of non zero coefficients in generated cut;
+ Default: 50 */
+ void setLimit(int limit);
+ /** Get value of limit */
+ int getLimit() const;
+
+ /** Set away, the minimum distance from being integer used for selecting
+ rows for cut generation; all rows whose pivot variable should be
+ integer but is more than away from integrality will be selected;
+ Default: 0.05 */
+ void setAway(double value);
+ /// Get value of away
+ double getAway() const;
+ /** Set the value of LUB, value considered large for the absolute value of
+ a lower or upper bound on a variable;
+ Default: 1000 */
+ void setLUB(double value);
+ /** Get the value of LUB */
+ double getLUB() const;
+
+ /** Set the value of EPS, epsilon for double computations;
+ Default: 1e-7 */
+ void setEPS(double value);
+ /** Get the value of EPS */
+ double getEPS() const;
+
+ /** Set the value of EPS_COEFF, epsilon for values of coefficients;
+ Default: 1e-8 */
+ void setEPS_COEFF(double value);
+ /** Get the value of EPS_COEFF */
+ double getEPS_COEFF() const;
+
+ /** Set the value of EPS_COEFF_LUB, epsilon for values of coefficients for
+ variables with absolute value of lower or upper bound larger than LUB;
+ Default: 1e-13 */
+ void setEPS_COEFF_LUB(double value);
+ /** Get the value of EPS_COEFF_LUB */
+ double getEPS_COEFF_LUB() const;
+
+ /** Set the value of EPS_RELAX, value used for relaxing the right hand side
+ of each generated cut;
+ Default: 1e-8 */
+ void setEPS_RELAX(double value);
+ /** Get the value of EPS_RELAX */
+ double getEPS_RELAX() const;
+
+ /** Set the value of normIsZero, the threshold for considering a norm to be
+ 0; Default: 1e-5 */
+ void setNormIsZero(double value);
+ /** Get the value of normIsZero */
+ double getNormIsZero() const;
+
+ /** Set the value of minReduc, threshold for relative norm improvement for
+ performing a reduction; Default: 0.05 */
+ void setMinReduc(double value);
+ /// Get the value of minReduc
+ double getMinReduc() const;
+
+ /** Set the maximum allowed value for (mTab * mTab * CoinMax(mTab, nTab)) where
+ mTab is the number of rows used in the combinations and nTab is the
+ number of continuous non basic variables. The work of the generator is
+ proportional to (mTab * mTab * CoinMax(mTab, nTab)). Reducing the value of
+ maxTab makes the generator faster, but weaker. Default: 1e7. */
+ void setMaxTab(double value);
+ /// Get the value of maxTab
+ double getMaxTab() const;
+ // END TO BE REMOVED
+ //************************************************************
+
+ //@}
+
+ /**@name Constructors and destructors */
+ //@{
+ /// Default constructor
+ CglRedSplit();
+
+ /// Constructor with specified parameters
+ CglRedSplit(const CglRedSplitParam &RS_param);
+
+ /// Copy constructor
+ CglRedSplit (const CglRedSplit &);
+
+ /// Clone
+ virtual CglCutGenerator * clone() const;
+
+ /// Assignment operator
+ CglRedSplit &
+ operator=(
+ const CglRedSplit& rhs);
+
+ /// Destructor
+ virtual
+ ~CglRedSplit ();
+ /// Create C++ lines to get to current state
+ virtual std::string generateCpp( FILE * fp);
+ //@}
+
+private:
+
+ // Private member methods
+
+/**@name Private member methods */
+
+ //@{
+
+ // Method generating the cuts after all CglRedSplit members are properly set.
+ void generateCuts(OsiCuts & cs);
+
+ /// Compute the fractional part of value, allowing for small error.
+ inline double rs_above_integer(double value);
+
+ /// Perform row r1 of pi := row r1 of pi - step * row r2 of pi.
+ void update_pi_mat(int r1, int r2, int step);
+
+ /// Perform row r1 of tab := row r1 of tab - step * row r2 of tab.
+ void update_redTab(int r1, int r2, int step);
+
+ /// Find optimal integer step for changing row r1 by adding to it a
+ /// multiple of another row r2.
+ void find_step(int r1, int r2, int *step,
+ double *reduc, double *norm);
+
+ /// Test if an ordered pair of rows yields a reduction. Perform the
+ /// reduction if it is acceptable.
+ int test_pair(int r1, int r2, double *norm);
+
+ /// Reduce rows of contNonBasicTab.
+ void reduce_contNonBasicTab();
+
+ /// Generate a row of the current LP tableau.
+ void generate_row(int index_row, double *row);
+
+ /// Generate a mixed integer Chvatal-Gomory cut, when all non basic
+ /// variables are non negative and at their lower bound.
+ int generate_cgcut(double *row, double *rhs);
+
+ /// Generate a mixed integer Chvatal-Gomory cut, when all non basic
+ /// variables are non negative and at their lower bound (different formula)
+ int generate_cgcut_2(int basic_ind, 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, double *slack_val);
+
+ /// Return the scale factor for the row.
+ /// Compute max_coeff: maximum absolute value of the coefficients.
+ /// Compute min_coeff: minimum absolute value of the coefficients
+ /// larger than EPS_COEFF.
+ /// Return -1 if max_coeff < EPS_COEFF or if max_coeff/min_coeff > MAXDYN
+ /// or MAXDYN_LUB (depending if the row has a non zero coeff. for a variable
+ /// with large lower/upper bound) */.
+ double row_scale_factor(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);
+
+ /// Check that the generated cuts do not cut a given optimal solution.
+ void check_optsol(const int calling_place,
+ const double *xlp, const double *slack_val,
+ const int do_flip);
+
+ /// Check that the generated cuts do not cut a given optimal solution.
+ void check_optsol(const int calling_place,
+ const double *xlp, const double *slack_val,
+ const double *ck_row, const double ck_rhs,
+ const int cut_number, const int do_flip);
+
+ // Check that two vectors are different.
+ bool rs_are_different_vectors(const int *vect1,
+ const int *vect2,
+ const int dim);
+
+ // Check that two vectors are different.
+ bool rs_are_different_vectors(const double *vect1,
+ const double *vect2,
+ const int dim);
+
+ // Check that two matrices are different.
+ bool rs_are_different_matrices(const CoinPackedMatrix *mat1,
+ const CoinPackedMatrix *mat2,
+ const int nmaj,
+ const int nmin);
+ //@}
+
+
+ // Private member data
+
+/**@name Private member data */
+
+ //@{
+
+ /// Object with CglRedSplitParam members.
+ CglRedSplitParam param;
+
+ /// Number of rows ( = number of slack variables) in the current LP.
+ int nrow;
+
+ /// Number of structural variables in the current LP.
+ int ncol;
+
+ /// 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;
+
+ /// 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 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
+ /// with non integer value in the current lp solution.
+ int *cv_intBasicVar_frac;
+
+ /// List of integer structural basic variables
+ /// (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_frac).
+ 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;
+
+ /// Current tableau for continuous non basic variables (structural or slack).
+ /// Only rows used for generation.
+ /// Dimensions: mTab by nTab.
+ double **contNonBasicTab;
+
+ /// Current 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 ;
+
+ /// Given optimal solution that should not be cut; only for debug.
+ const double *given_optsol;
+
+ /// Number of entries in given_optsol.
+ int card_given_optsol;
+
+ /// Characteristic vectors of structural integer variables or continuous
+ /// variables currently fixed to integer values.
+ int *is_integer;
+
+ /// Characteristic vector of the structural variables whose lower bound
+ /// in absolute value is larger than LUB.
+ int *low_is_lub;
+
+ /// Characteristic vector of the structural variables whose upper bound
+ /// in absolute value is larger than LUB.
+ int *up_is_lub;
+
+ /// 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 column type. Reset by each call to generateCuts().
+ const char *colType;
+
+ /// Pointer on matrix of coefficient ordered by rows.
+ /// Reset by each call to generateCuts().
+ const CoinPackedMatrix *byRow;
+
+ //@}
+};
+
+//#############################################################################
+/** A function that tests the methods in the CglRedSplit 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 CglRedSplitUnitTest(const OsiSolverInterface * siP,
+ const std::string mpdDir );
+
+
+#endif